Lassa virus (LASV), an arenavirus endemic to West Africa, causes Lassa fever—a lethal hemorrhagic fever. Entry of LASV into the host cell is mediated by the glycoprotein complex (GPC), which is the only protein located on the viral surface and comprises three subunits: glycoprotein 1 (GP1), glycoprotein 2 (GP2), and a stable signal peptide (SSP). The LASV GPC is a class one viral fusion protein, akin to those found in viruses such as human immunodeficiency virus (HIV), influenza, Ebola virus (EBOV), and severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). These viruses are enveloped and utilize membrane fusion to deliver their genetic material to the host cell. Like other class one fusion proteins, LASV-mediated membrane fusion occurs through an orchestrated sequence of conformational changes in its GPC. The receptor-binding subunit, GP1, first engages with a host cell receptor then undergoes a unique receptor switch upon delivery to the late endosome. The acidic pH and change in receptor result in the dissociation of GP1, exposing the fusion subunit, GP2, such that fusion can occur. These events ultimately lead to the formation of a fusion pore so that the LASV genetic material is released into the host cell. Interestingly, the mature GPC retains its SSP as a third subunit—a feature that is unique to arenaviruses. Additionally, the fusion domain contains two separate fusion peptides, instead of a standard singular fusion peptide. Here, we give a comprehensive review of the LASV GPC components and their unusual features.

The Mammarenavirus genus of the Arenaviridae family comprises a diverse group of enveloped, negative-sense single-stranded RNA viruses and can be divided into two categories, Old-World (OW) or New-World (NW), based on phylogenetic differences and geographical distribution [1,2]. OW arenaviruses are those that circulate in Africa, Asia and Europe, whereas those classified as NW circulate in the Americas [3]. Various species of rodents are the natural reservoirs for these viruses with endemicity dependent on the species’ indigenous location. Several viruses in this family are pathogenic in humans and are causative agents of viral hemorrhagic fevers [4]—one of which, Lassa virus (LASV), an OW arenavirus, will be the focus of this review article.

LASV is endemic to West Africa and is the most prevalent arenavirus afflicting humans [5,6]. It is primarily spread by direct contact with excrement from infected Mastomys natalensis rodents and, rarely, between humans by bodily fluids [7–12]. Infection with LASV causes Lassa fever, a hemorrhagic fever with high morbidity and mortality that affects an estimated 100000–300000 individuals annually [10–15]. The case fatality rate (CFR) of LASV historically averages ∼20% [16–19]. For perspective, the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) pandemic CFR averaged between 1 and 3% [20–25]. Despite the high pathogenicity of LASV, there are currently no FDA-approved vaccines or antivirals for the explicit treatment of Lassa fever [13,26–29]. Therapeutic options are limited to off-label usage of the antiviral ribavirin, which is only effective in the early stages of infection and has severe side effects, and induction of passive immunity with survivors’ antibodies [11–13,29–32]. Several small-molecule compounds that inhibit arenavirus entry have recently been described and show promise in vitro but have not yet advanced past laboratory studies [28,33–42]. Recently, the attenuated Candid#1 vaccine was shown to be effective against Junín virus (JUNV), an NW arenavirus that is the causative agent of Argentine hemorrhagic fever [43,44]. However, the vaccine is ineffective against LASV [45–49]. This has largely been attributed to ample glycosylation of the LASV glycoprotein complex (GPC) that provides immunological resistance [50–54]. Given the relatively high CFR of LASV infections combined with its high infectivity and minimal treatment options, this virus has the potential to be a great risk to public health following the completion of the zoonotic jump. Accordingly, LASV has been categorized as a category A, biosafety level 4 agent by the Centers for Disease Control and Prevention [55]. The World Health Organization also lists LASV as one of the top five infectious diseases requiring prioritized research due to its threat to public health [56,57].

Delivery of LASV’s genetic material into the host cell is an integral component of its lifecycle. LASV contains a class one fusion protein, akin to those found in human immunodeficiency virus (HIV), Ebola virus (EBOV), SARS-CoV-2, and influenza. These viruses are enveloped and must utilize membrane fusion to deliver their genetic material. The generally accepted model for this process involves the formation of a fusion pore between the host and viral membranes [58–65]. This process is achieved by a glycoprotein located on the virion surface that undergoes a dramatic, energetically favorable conformational change [66–70]. LASV fusion is mediated by the surface GPC, which exists on the virion surface as a trimer of tripartite GPC monomers [71]. GPC is initially expressed as a single polypeptide and undergoes proteolytic cleavage to yield three subunits: glycoprotein 1 (GP1), glycoprotein 2 (GP2), and the stable signal peptide (SSP) (Figure 1A,B) [62,72]. GP1 interacts with host cell receptors, GP2 facilitates membrane fusion, and SSP has various roles, including sensing pH changes to prompt fusion under appropriate conditions, stabilizing GP2’s intermediate conformation, and intracellular trafficking of the GPC precursor [73–75].

Schematic representation of the LASVGPC

Figure 1
Schematic representation of the LASVGPC

(A) The GPC open-reading frame is diagrammed with the cleavage sites of SPase and SKI-1/S1P indicated. In SSP (pink), the myristoylation at glycine 2 is marked. The eleven N-glycosylation motifs are denoted at their respective locations in the mature GP1 (dark blue) and GP2 (gray) subunits. (B) Cartoon illustration of the GPC trimer as it would appear embedded with in the viral membrane (tan). (C) An illustration of GPC’s involvement in the LASV viral lifecycle. GP1 binds to the host receptor (1) before being endocytosed (2). Upon internalization, the virion is delivered to the late endosome where GP1 engages with the intracellular receptor LAMP1 (3). GP1 dissociates so that GP2 is exposed and can mediate membrane fusion leading to the delivery of the viral genome into the host cell cytoplasm (4). The genome is directed to the endoplasmic reticulum where it is transcribed, translated, and replicated (5) before being trafficked to the plasma membrane for assembly and budding (6). Abbreviations: LAMP1, lysosomal-associated membrane protein 1; SPase, cellular signal peptidase.

Figure 1
Schematic representation of the LASVGPC

(A) The GPC open-reading frame is diagrammed with the cleavage sites of SPase and SKI-1/S1P indicated. In SSP (pink), the myristoylation at glycine 2 is marked. The eleven N-glycosylation motifs are denoted at their respective locations in the mature GP1 (dark blue) and GP2 (gray) subunits. (B) Cartoon illustration of the GPC trimer as it would appear embedded with in the viral membrane (tan). (C) An illustration of GPC’s involvement in the LASV viral lifecycle. GP1 binds to the host receptor (1) before being endocytosed (2). Upon internalization, the virion is delivered to the late endosome where GP1 engages with the intracellular receptor LAMP1 (3). GP1 dissociates so that GP2 is exposed and can mediate membrane fusion leading to the delivery of the viral genome into the host cell cytoplasm (4). The genome is directed to the endoplasmic reticulum where it is transcribed, translated, and replicated (5) before being trafficked to the plasma membrane for assembly and budding (6). Abbreviations: LAMP1, lysosomal-associated membrane protein 1; SPase, cellular signal peptidase.

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LASV follows the general Arenaviridae lifecycle (Figure 1C) where host cell entry is mediated by engagement with a host cell receptor, followed by endocytosis [76–80]. During viral entry, GP1 is responsible for binding at least two different cellular receptors: α-dystroglycan (αDG) followed by lysosomal-associated membrane protein 1 (LAMP1). This receptor switch is pH-dependent and unique to LASV as it is not observed in any other arenaviruses [79]. GP1 first engages with the host cell receptor αDG that is located on the plasma membrane. The virion is then internalized and delivered to the late endosome, which is where the membrane fusion event ultimately transpires. The low-pH environment of this compartment triggers GP1 to undergo conformational changes that cause it to now engage with the intracellular receptor LAMP1. This leads to the dissociation of GP1 from the GPC, which results in the exposure of the fusion peptide at the N-terminus of GP2 [77,80–82]. The fusion peptide inserts into the lysosomal membrane, resulting in a metastable pre-hairpin structure, which spontaneously folds back on itself to form a six-helix bundle (6HB), overcoming the energy barrier associated with the fusion of the host and viral membranes. The formation of the 6HB brings the virion and lysosomal membranes in proximity leading to the opening of a fusion pore and delivery of the viral genome into the host cell cytoplasm (Figure 2) [60,82].

Membrane fusion illustration

Figure 2
Membrane fusion illustration

(1.) The pre-fusion structure of GPC in the viral membrane (tan) is shown. (2.) Upon delivery to the acidic lysosome, GP1 (dark blue) engages with LAMP1 resulting in its dissociation from GPC as triggered by the low pH. GP2 (light gray) becomes unclamped such that the fusion peptide and internal fusion loop at the N-terminus of GP2 (red) are now exposed and inserted into the lysosomal membrane (light blue), forming a metastable pre-fusion hairpin. (3.) GP2 then folds back on itself in an energetically favorable rearrangement. This forms the 6HB and brings the host cell and viral membranes in proximity. (4.) The two membranes then fuse (green), which forms a complete fusion pore and final post-fusion state that exists as a trimer of GP2-SSP. From here the viral genome is released into the cytosol.

Figure 2
Membrane fusion illustration

(1.) The pre-fusion structure of GPC in the viral membrane (tan) is shown. (2.) Upon delivery to the acidic lysosome, GP1 (dark blue) engages with LAMP1 resulting in its dissociation from GPC as triggered by the low pH. GP2 (light gray) becomes unclamped such that the fusion peptide and internal fusion loop at the N-terminus of GP2 (red) are now exposed and inserted into the lysosomal membrane (light blue), forming a metastable pre-fusion hairpin. (3.) GP2 then folds back on itself in an energetically favorable rearrangement. This forms the 6HB and brings the host cell and viral membranes in proximity. (4.) The two membranes then fuse (green), which forms a complete fusion pore and final post-fusion state that exists as a trimer of GP2-SSP. From here the viral genome is released into the cytosol.

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GPC and its components prove an interesting target for potential therapeutics owing to its location on the surface of the viral envelope and its central role in membrane fusion, a required step in the viral life cycle. Interestingly, compared with other class one fusion proteins, LASV has several unique structural features including the receptor switch from αDG to LAMP1 as mediated by GP1 and the resulting low pH for optimal fusion. Moreover, another unique feature of LASV is that the fusion peptide contains two distinct components: an N-terminal fusion peptide (NFP), similar to HIV and influenza, and an internal fusion loop (IFL) with a disulfide bond, similar to EBOV. The only other class one fusion protein shown to have both an NFP and IFL are coronaviruses [83–88]. The unusual retention of SSP also has intriguing roles in GPC synthesis and maturation as well as fusion activity [74,75,89–91]. Due to the existence of several excellent review articles on LASV epidemiology, life cycle, and genomic organization [92–98], we will be focusing our discussion on the GPC components and their distinctive properties as related to membrane fusion. All arenaviruses have strong sequence conservation and use a similar mechanism to enter the host cell. As a result, viruses within the same category are often cross-analyzed. Therefore, this review will use evidence from LASV and other arenaviruses, such as lymphocytic choriomeningitis virus (LCMV), another OW arenavirus that is genetically and serologically similar to LASV, and JUNV. For clarity purposes, any non-LASV residues will be followed by the corresponding LASV residue in parentheses.

Maturation of the GPC yields three components

To fully comprehend the uniqueness of the LASV GPC components, one must first understand the intricacies leading to their development. Like other class one glycoproteins, GPC is first synthesized as a precursor polypeptide that is subsequently cleaved by host cell peptidases to yield the mature GPC. For LASV, GPC is synthesized from the RNA genome as a precursor that is directed to the endoplasmic reticulum. Here, the mature SSP is created via cellular signal peptidase (SPase) cleavage but remains noncovalently associated with the GPC [89]. At the same time, the GPC precursor is translated and undergoes N-linked glycosylation. There are 11 N-glycosylation motifs (N–X–S/T where X is any amino acid, except proline) within the LASV GPC with seven located in GP1 and four in GP2 (Figure 1A) [71,99]. The four glycosylation sites within GP2 are highly conserved across most arenaviruses, whereas the number of glycosylation sites in GP1 varies considerably. This extensive amount of N-linked glycosylation is often referred to as a glycan shield and leaves few regions open to antibody binding. Glycosylation therefore has implications in the arenavirus’ ability to evade antibody-mediated immune responses as the epitope is masked [50–54,62]. These glycosylation motifs are also involved in GP1 receptor recognition, which will be examined in detail shortly [100–102].

For all class one glycoproteins, the precursor fusion protein must be primed via proteolytic cleavage before it can be triggered to induce fusion. For LASV, this priming event occurs after glycosylation and SSP cleavage when the GPC is translocated to the Golgi apparatus as directed by the SSP. Here, the precursor GPC undergoes post-translational proteolytic cleavage by subtilase/kexin isozyme-1 (SKI-1/S1P) to yield the mature GPC containing the GP1 and GP2 components [75,103–106]. For other class one glycoproteins, the signal peptide’s function has been served following final protein localization, so it is degraded and not retained in the mature glycoprotein [60]. Interestingly, the LASV SSP remains associated with the mature GPC—a feature that is unique to arenaviruses and will thus be covered in depth later in this review article. The SSP, GP1, and GP2 are noncovalently bound to each other and form a novel structure not observed in other class one fusion proteins (Figure 1B) [107]. The GPC is then trafficked to the cellular plasma membrane for virion assembly and budding, where it is incorporated on to the surface of the viral envelope (Figure 1C) [108,109]. It is this mature GPC and its components that are responsible for LASV entry.

Receptor binding occurs via GP1

LASV entry is a multistep process that is first facilitated by GP1, which is 200 amino acids in length and spans from T59 to L259 of the mature GPC. Initially, GP1 binds with a host cell receptor located on the plasma membrane, specifically the α subunit of dystroglycan (Figure 3A) [110,111]. After binding to αDG, LASV is endocytosed into the host cell, then delivered to the late endosome where it engages with the intracellular receptor LAMP1. This receptor switch is unique to LASV and not observed in other arenaviruses.

Crystal structure (PDB: 5VK2) of LASV GP1 trimer from the top (upper) and side (lower) views

Figure 3
Crystal structure (PDB: 5VK2) of LASV GP1 trimer from the top (upper) and side (lower) views

(A) Cartoon representation of GP1 (cyan) as it appears when associated with GP2 (gray). (B) A surface model of GP1 is presented with the RBD1 highlighted. Residues implicated in αDG-binding cluster in the top central core of GP1, forming the αDG-binding site (purple). The glycosylation motif at N119 (pink) is located near this site but does not occlude it. It is important to note that the crystal structure lacks a glycan in the third GP1 subunit, which would be present in vivo. (C) The RBD2 of GP1 is represented via a surface model. A histidine triad (yellow) forms the LAMP1-binding site. Protonation of this triad leads to a conformational change that exposes the RBD2. However, this triad is shielded by the glycosylation motif at N89 (black) in the pre-fusion state, which particularly packs against H92. At low pH, this glycan is shifted away to allow for LAMP1 binding. Abbreviation: RBD1/2, receptor-binding domain 1/2.

Figure 3
Crystal structure (PDB: 5VK2) of LASV GP1 trimer from the top (upper) and side (lower) views

(A) Cartoon representation of GP1 (cyan) as it appears when associated with GP2 (gray). (B) A surface model of GP1 is presented with the RBD1 highlighted. Residues implicated in αDG-binding cluster in the top central core of GP1, forming the αDG-binding site (purple). The glycosylation motif at N119 (pink) is located near this site but does not occlude it. It is important to note that the crystal structure lacks a glycan in the third GP1 subunit, which would be present in vivo. (C) The RBD2 of GP1 is represented via a surface model. A histidine triad (yellow) forms the LAMP1-binding site. Protonation of this triad leads to a conformational change that exposes the RBD2. However, this triad is shielded by the glycosylation motif at N89 (black) in the pre-fusion state, which particularly packs against H92. At low pH, this glycan is shifted away to allow for LAMP1 binding. Abbreviation: RBD1/2, receptor-binding domain 1/2.

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LASV first engages with host cell receptors at the plasma membrane to enter the host cell

Dystroglycan is a highly conserved cell-surface glycoprotein that is synthesized as a single protein before undergoing post-translational cleavage to yield αDG, the peripheral protein, and βDG, the transmembrane protein [112–115]. It is involved in extracellular matrix adhesion and is a critical component for membrane integrity in numerous cell types, including nerve and muscle cells. In the host cell, αDG is subjected to extensive post-translational modifications, including glycosylation that is critical for its function as an extracellular matrix receptor and arenavirus-binding site [111,116–124]. Regardless, the expression of functional αDG has been demonstrated to be insufficient for productive entry of LASV, but the exact factors that influence entry remain unclear [125]. In the absence of αDG, it has been suggested that GP1 can interact with heparan sulfate, dendritic cell-specific intercellular adhesion molecule-3-grabbing nonintegrin (DC-SIGN), liver and lymph node sinusoidal endothelial cell C-type lectin (LSECtin), and Tyro3/Axl/Mer (TAM) family members to gain entry—albeit with reduced infectivity [78,126–130]. Interestingly, these receptors have been shown to play a role in the entry of several other viruses, including EBOV, dengue virus, ZIKA virus, and SARS coronaviruses [131–138]. This highlights the remarkable adaptability of LASV in the entry process.

Mutational analysis of GP1 has highlighted a potential receptor-binding domain (RBD1) at the top central core of the GPC trimer that is important in αDG binding [139]. Residues H141, N146, F147, and Y150 cluster in this core interface and were implicated in the αDG-binding site (Figure 3B, purple) [139]. Coincidentally, the glycosylation motif at N119 is located near this binding site but does not occlude it (Figure 3B, pink) [50,51]. An N119Q mutation revealed that this glycan protects the αDG-binding site from antibody-mediated neutralization by shielding the epitope [50,53]. The necessity of glycosylation for efficient αDG binding by GP1 has also been validated by inhibition experiments [140]. Additionally, residues located in the same region at the top central core of the LCMV GP1 were implicated in αDG binding [141–143]. This includes S153 (N148), Y155 (Y150), R190 (G186), and F260 (I254), further strengthening the importance of this region for function as RBD1 (Figure 3B, purple).

A unique receptor switch by LASV occurs after endocytosis

Initially, it was suggested that LASV cell entry occurred via clathrin-mediated endocytosis [144], but subsequent studies described the usage of a clathrin- and dynamin-independent pathway [6,76,145,146]. Genome-wide RNA interference silencing screens identified sodium hydrogen exchangers (NHEs), which have previously been implicated in macropinocytosis, as host factors involved in the multiplication of LCMV [147,148]. In a successive study, NHE was validated to be the entry factor and was thus indicative that LASV enters the host cell through macropinocytosis [146,149]. This type of endocytosis involves the nonspecific uptake of extracellular molecules via large vacuoles [150]. Intriguingly, macropinocytosis is the entry pathway for over 20 viruses, including HIV, herpes simplex virus 1, and EBOV [151–156].

Upon macropinocytosis, the virion is internalized and delivered to the late endosome where fusion ultimately takes place. Studies have shown that LASV-mediated fusion occurs at an unusually acidic pH of below 5.0 with optimal fusion suggested to occur at a pH of ∼4.0 [157–159]. While extremely low pH is likely sufficient enough to trigger fusion, successful and efficient LASV entry requires GP1 to undergo a unique receptor switch from αDG to LAMP1 [78]. Like αDG, LAMP1 must be glycosylated for this engagement to occur as previous studies showed that an N-linked glycan in this receptor was a critical determinant in LASV binding [78,160]. Binding to LAMP1, which is localized to the inner membrane of the late endosome/lysosome, shifts the pH of optimal fusion to be less acidic [159,161]. Engagement with LAMP1 thus increases the efficiency of LASV fusion, but the exact role remains to be clarified. No other OW arenavirus has been shown to interact with LAMP1, regardless of full conservation of the LAMP1-binding site in GP1. This receptor switch is thus unique to LASV [160]. Thus far, the only other virus shown to utilize late endosome receptor-assisted fusion is EBOV, but again the exact mechanism remains unclear.

It has been shown that in the low pH environment of the late endosomal compartment, GP1 undergoes irreversible conformational changes that decrease its affinity for αDG while increasing its affinity for the acidic LAMP1 receptor [78,161,162]. Structural and mutational analysis has revealed a highly conserved histidine triad (H92/93/230) in GP1 that forms the LAMP1-binding site and second receptor-binding domain (RBD2) (Figure 3C, yellow) [139,163–165]. Protonation in this triad, specifically H230, has been proposed to facilitate conformational changes that expose the LAMP1-binding site [164–166]. Curiously, GP1 glycosylation motif at N89 was reported to shield the histidine triad in the pre-fusion conformation before being redirected after endocytosis to allow for LAMP1 binding (Figure 3C, black) [51,71,167]. More specifically, H92 packs against N89 at physiological pH, but N89 is shifted ∼10 Å away at low pH [101]. This further supports the notion that glycosylation is involved in receptor recognition and binding by GP1. Moreover, at neutral pH, H93 makes a hydrogen bond with the main chain oxygen of N90 [71]. When the pH is reduced, H93 rotates such that it is no longer capable of making this hydrogen bond. It thus appears that modifications in the location of the glycosylation motif at N89 and hydrogen bonding result in the opening of the binding site so that the histidine triad may engage with LAMP1. Additionally, four other residues (L84N, K88E, L107F, and H170S) that neighbor the histidine triad were identified that decrease LAMP1-binding affinity when mutated and thus may be involved in the binding site as well [168]. It is interesting that another histidine may be important in LAMP1 binding that exists outside RBD2.

To summarize, GP1 serves as the R for arenaviruses. GP1 will first engage with the host cell receptor on the plasma membrane, primarily αDG, then be endocytosed via macropinocytosis. Fusion occurs upon the virion’s delivery to the late endosome. In LASV, this is a multistep process that involves a receptor switch from the primary receptor, αDG, to the intracellular receptor, LAMP1. We anticipate future experimentation will likely delve into why LASV is the only arenavirus to utilize assisted fusion and a receptor switch. Previous work has already suggested that engagement with LAMP1 increases fusion efficiency, but whether this has any implications in LASV morbidity remains unclear. Investigation into the underlying molecular mechanisms of immune evasion and the residues involved in this interaction may answer this question. Additionally, given GP1’s critical role in viral entry, deducing these mechanisms would have serious impacts on the development of therapeutic interventions.

Membrane fusion is mediated by GP2

GP2 is 231 amino acids in length and spans from G260 to R491 of the GPC (Figure 4A,B). Structurally, GP2 has the principle features of a class one fusion protein and is categorized as such due to its largely α-helical secondary structure and two heptad repeat (HR) regions that are preceded by a fusion peptide [59,81,169–171]. There are eight known domains of the GP2 including the NFP (G260–P275), IFL (G276–N295), heptad repeat 1 (HR1) (E308–S358), T-loop (C364–C385), heptad repeat 2 (HR2) (N395–I411), membrane proximal external region (MPER, T412–P427) transmembrane domain (TM, L428–L447), and C-terminal cytoplasmic tail (H448–R491) [9,157]. For this review article, we will be grouping these domains into three sections: fusion domain (NFP and IFL), coiled-coil (HR1, T-loop, and HR2), and C-terminus region (MPER, TM, and cytoplasmic tail).

Sequence and structure of the LASV GP2

Figure 4
Sequence and structure of the LASV GP2

(A) The known domains of GP2 are color-coded: NFP (red); IFL (orange); HR1 (yellow); T-loop (green); HR2 (blue); MPER (purple); TM (black); cytoplasmic tail (gray). (B) Cartoon representation of the pre-fusion crystal structure of a GP2 monomer (PDB: 5VK2). (C) Sequence alignment of the NFP and IFL of pathogenic and/or OW arenaviruses with numbering according to the LASV sequence. Pathogenic arenaviruses are denoted via **. The prototypic Pichinde virus is also shown. Residues with full conservation are indicated by an asterisk (*), whereas those with strongly and weakly similar properties are shown via a semicolon (:) and period (.), respectively. Abbreviations: CHAVB, Chapare virus; DNDV, Dandenong virus; GTOV, Guanarito virus; IPPYV, Ippy virus; LUJOV, Lujo virus; MACV, Machupo virus; MOBV, Mobala virus; MOPV, Mopeia virus; PICV, Pichinde virus; SABV, Sabia virus; WWAV, Whitewater Arroyo virus.

Figure 4
Sequence and structure of the LASV GP2

(A) The known domains of GP2 are color-coded: NFP (red); IFL (orange); HR1 (yellow); T-loop (green); HR2 (blue); MPER (purple); TM (black); cytoplasmic tail (gray). (B) Cartoon representation of the pre-fusion crystal structure of a GP2 monomer (PDB: 5VK2). (C) Sequence alignment of the NFP and IFL of pathogenic and/or OW arenaviruses with numbering according to the LASV sequence. Pathogenic arenaviruses are denoted via **. The prototypic Pichinde virus is also shown. Residues with full conservation are indicated by an asterisk (*), whereas those with strongly and weakly similar properties are shown via a semicolon (:) and period (.), respectively. Abbreviations: CHAVB, Chapare virus; DNDV, Dandenong virus; GTOV, Guanarito virus; IPPYV, Ippy virus; LUJOV, Lujo virus; MACV, Machupo virus; MOBV, Mobala virus; MOPV, Mopeia virus; PICV, Pichinde virus; SABV, Sabia virus; WWAV, Whitewater Arroyo virus.

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Unique properties of the LASV fusion domain

LASV GP2 follows the generally accepted model for the function of class one viral fusion proteins where the fusion mechanism is mediated by its refolding to form a 6HB. For LASV, this occurs after GP1 dissociation where GP2 is uncovered so that the fusion peptide is now exposed. Class one viral fusion proteins all contain a hydrophobic sequence that is responsible for engaging the target membrane and thus bridging the host and viral membranes. Typically, this is either an NFP or IFL located within the fusion subunit of the surface glycoprotein. Most often, class one fusion proteins have been found to contain an NFP, except for EBOV which has an IFL [172]. However, in the case of LASV and the arenavirus family, both an NFP and IFL are present and create a fusion domain that initiates fusion by targeting the host cell membrane [157,173,174]. Thus far, the only other class one fusion protein with this characteristic are coronaviruses, potentially contributing to their remarkable infectivity [83–88].

The LASV fusion domain is moderately conserved among all OW and/or pathogenic arenaviruses (Figure 4C). Furthermore, the canonical fusion motif Gly-X-Phe located at the N-terminus of the fusion domain is also highly conserved among OW arenaviruses where X is either T or L [175]. This motif has been established in fusion peptides of other viruses, like HIV and influenza [176]. Single-point mutations to alanine for each hydrophobic amino acid in the fusion domain resulted in a significant reduction or abolishment of fusogenicity, validating the involvement of both the NFP and IFL in fusion [157]. Multiple residues were shown to impact fusogenicity through in vitro studies including G260A/R, F262A, W264A, G271A, which are all located in the NFP, and G277A, Y278A, L280A, W283A, L290A, and G294A located in the IFL. Four of these residues are well conserved across all arenaviruses and were indicated as critical for efficient fusion: W264, G277, Y278, and L280. Mutations in this region likely reduce the hydrophobicity of the fusion domain, which inhibits adequate insertion into the target membrane to facilitate fusion. This further strengthens the postulation that both the NFP and IFL are required for efficient fusion.

Nonetheless, the necessity for both fusion peptides in LASV and their exact mechanism of action remains poorly understood. The pre-fusion structure of these two proteins has been characterized as a random coil with the only discernible secondary structural element being a disulfide bond [71]. On the other hand, these proteins have been omitted from post-fusion structures of GP2 and thus remains unsolved [169,170]. Thus, future experiments will likely be centered around solving the post-fusion structure of the fusion domain to fill this knowledge gap. We anticipate that subsequent studies will investigate the residue-specific interactions that are critical to the function of the LASV fusion domain.

Coiled-coil structure further classifies LASV as a class one fusion protein

Now that we have finished discussing the LASV fusion domain, we must highlight another major defining characteristic of class one fusion proteins—the formation of the 6HB. In both their pre- and post-fusion states, class one glycoproteins exist as trimers. In the pre-fusion state, the HR1 and HR2 trimers exist independently as α helices that are connected by the T-loop (Figure 5A). The T-loop itself does not appear to have a function aside from connecting the HR1 and HR2 [177]. Following the initiation of membrane fusion, a prehairpin intermediate structure is formed where the HR1 sits atop the HR2 in an antiparallel manner. HR1 and HR2 coordinate with each other to form the coiled-coil where a central HR1 trimer is surrounded by three HR2. The intermediate structure spontaneously collapses on itself where the three HR2 pack on to the outside of the central trimeric HR1 core to create the 6HB (Figure 5B). This formation of the 6HB is energetically favorable and the major driving force for fusion as it brings the target and virion membranes nearby such that they may fuse. Ultimately, the final post-fusion conformation of the trimer-of-hairpins is achieved, and a complete fusion pore is formed.

Representation of the LASV coiled-coil in different states
Figure 5
Representation of the LASV coiled-coil in different states

(A) The pre-fusion state of the LASV HR1 (yellow) and HR2 (blue) trimers that exist independently but are connected by the T-loop (green). No helical core is present with the trimers oriented nearly perpendicular to the threefold axis (PDB: 5VK2). (B) In the post-fusion state, the HR1, HR2, and T-loop unravel and reorient to form the characteristic coiled-coil/6HB. A central trimer of HR1 is surrounded by three HR2. Each monomer is connected by a T-loop (PDB: 5OMI). (C) A monomer of the coiled-coil is presented with the residues that form salt bridges indicated in black. (D) A surface model of the coiled-coil (PDB: 5OMI). The hydrophobic interactions (red) between adjacent HR1 and HR2 monomers of the 6HB form a core that is further stabilized by salt bridges (black). (E) The sequence of the LASV HRs as connected by the T-loop. Residues that form salt bridges are shown in black and linked to their corresponding ionic partner, while residues involved in the hydrophobic core are shown in red.

Figure 5
Representation of the LASV coiled-coil in different states

(A) The pre-fusion state of the LASV HR1 (yellow) and HR2 (blue) trimers that exist independently but are connected by the T-loop (green). No helical core is present with the trimers oriented nearly perpendicular to the threefold axis (PDB: 5VK2). (B) In the post-fusion state, the HR1, HR2, and T-loop unravel and reorient to form the characteristic coiled-coil/6HB. A central trimer of HR1 is surrounded by three HR2. Each monomer is connected by a T-loop (PDB: 5OMI). (C) A monomer of the coiled-coil is presented with the residues that form salt bridges indicated in black. (D) A surface model of the coiled-coil (PDB: 5OMI). The hydrophobic interactions (red) between adjacent HR1 and HR2 monomers of the 6HB form a core that is further stabilized by salt bridges (black). (E) The sequence of the LASV HRs as connected by the T-loop. Residues that form salt bridges are shown in black and linked to their corresponding ionic partner, while residues involved in the hydrophobic core are shown in red.

Close modal

Typically, in class one fusion proteins the trimer is formed about a stabilizing central three-helical core with a threefold axis that remains largely unaffected between the pre- and post-fusion conformations [95]. Nonetheless, a pre-fusion LASV crystal structure was recently generated that demonstrated this core is nonexistent and GP2 is oriented nearly perpendicular to the threefold axis in the pre-fusion conformation (Figure 5A) [71]. To achieve the post-fusion conformation, every section of GP2 must thus unravel and reorient. The structure presented here aligned well with a previously determined structure of the LCMV GPC monomer. This reorientation is thus unique to arenaviruses [95]. Furthermore, alanine substitutions in JUNV at I333 (V341), L336 (L344), I347 (L355), and L350 (I358) in HR1 and R392 (S400) and W395 (I403) in HR2 resulted in reduced fusogenicity of the GP2 [178]. This infers that these buried residues are important in promoting fusion. In the pre-fusion conformation, these residues are positioned such that they have interhelical interactions that likely result in the stabilization of the coiled coil. In particular, R392 (S400) may impart specificity to the process of coiled-coil folding at the expense of protein stability [179].

In the post-fusion crystal structure, there are three HR1 helices in a coiled-coil orientation with three HR2 helices entwined in an antiparallel manner forming the 6HB [169,170]. The three HR1 helices were shown to be closely packed against each other by hydrophobic force in a parallel manner and create a central core [169]. The C-terminal HR2 adopts such an orientation that places its helix close to the N-terminal HR1 helices of the adjacent monomers. This positioning ultimately creates a hydrophobic core involving A407 and I411 of the HR2 and L313 and F316 of the adjacent HR1 (Figure 5C,D, red) [170]. The T-loop region and HR2 are packed against the hydrophobic grooves of the central coiled-coil. W386, V388, L394, and F399 of HR2 are deeply buried in these grooves of HR1 with many other long-chained, hydrophobic residues, such as I403 and M410, involved as well (Figure 5C,D, red). Granted, for stability purposes, only the HR1, T-loop, and HR2 domains of the LASV GP2 were included in this crystal structure [169] but aligned well with a similar reported LASV 6HB structure [170]. A separate study validated the necessity of L394 and I403 for GP2 function [9]. Additionally, using alanine scanning mutagenesis, I323 was identified as being critical for fusion and optimal GP2 function. This trend can likely be justified by the loss of hydrophobicity in this region, which does not allow for the efficient formation of the 6HB.

In addition to the hydrophobic interactions, several electrostatic interactions stabilize the 6HB. D347 and K352 of one HR1 domain bind to residues of opposite charges in the other two HR1 domains near the T-loop [169]. This interchain salt bridge was also found in the corresponding residues of LCMV and seemed to stabilize the end of the inner core [81]. Additional work on LCMV elucidated other stabilizing interactions, particularly multiple ionic interactions, which seem to also exist in LASV based on sequence homology and structural alignment. Two separate salt bridges exist between lysine side chains in the N-terminal helix and aspartate and/or glutamate side chains in the C-terminal helix. These are K326 (K320) with D414 (D408) and K333 (K327) with both D407 (D401) and E410 (E404) (Figure 5C–E, black). K331 (R325) and D335 (E329) form a salt bridge to connect two consecutive turns in the N-terminus helix (Figure 5C–E, black). These salt bridges are thus well conserved and aid in stabilization between GP2 monomers of the post-fusion conformation.

C-terminus region has multiple domains that are key to LASV fusogenicity

Our review of GP2 will conclude with a discussion of the C-terminus domains and their roles in fusogenicity. This includes the TM, cytoplasmic tail, and MPER, which is located between HR2 and TM from residues T412 to P427 (Figure 4A) [180]. In class one fusion proteins, namely EBOV and HIV, the MPER has been shown to have important functions in fusion and glycoprotein stabilization [181–186]. The MPER in HIV is the target of the broadest neutralizing antibodies and has implications in membrane fusion due to destabilizing effects on the lipid membrane [187–192]. Additionally, in EBOV, the MPER was shown to interact with its IFL and membrane lipids during fusion—potentially contributing to the driving force of 6HB formation to promote fusion [181,193]. Following this logic, the MPER in GP2 has been investigated for any impacts on LASV fusogenicity.

In LASV, the formation of the 6HB brings the fusion domain near the TM region, including the MPER, which may contribute to the driving force of fusion. This was investigated using alanine scanning mutagenesis of all 16 residues in the MPER [180]. It was revealed that M414 and L415 in the C-terminus of HR2 and K417 and Y419 in the N-terminus of the MPER were critical for membrane fusion (Figure 6A). Even though mature GPC was present with these mutants, it was nonfunctional and incapable of facilitating fusion. Mutation to a more conserved residue, such as M414L, L415I, K417R, and Y419F, resulted in partial recovery of fusogenicity. The finding that K417 is critical for GP2 function comes as no surprise since it is highly conserved and the equivalent lysine in Guanarito virus (GTOV), an NW arenavirus with pathogenicity in humans, forms a salt bridge with a conserved aspartate and glutamate in the adjacent HR1 [194]. Moreover, E418, R422, T426, and P427 all exhibited reduced fusogenic activity when mutated to alanine. R422 was validated as a critical residue for GP2 function in a separate study, but it is unclear if this residue forms a salt bridge, and if so, with what partner [9]. Altogether, this is indicative that the MPER is critical to the stability of GP2 with implications in efficient LASV-mediated fusion.

Characterization of the SSP and cytoplasmic tail of GP2
Figure 6
Characterization of the SSP and cytoplasmic tail of GP2

(A) Sequence alignment of the LASV GP2 C-terminus of pathogenic and/or OW arenaviruses. Residues in the MPER (purple), TM (shaded black), and cytoplasmic tail implicated in fusion are bolded. The ZBD1 (orange) and ZBD2 (red) are shown. (B) Illustration of the SSP (pink) and its association with the TM (black) of GP2 from the top and side view. Helix 1 (H1) creates an interface with the TM, whereas helix 2 (H2) contains C57, the fourth ligand in ZBD2 (red). ZBD1 (orange) is shown as well. Each ZBD coordinates with a zinc ion (purple) (C) Sequence alignment of the SSP with the myristoylation motif outlined in green. Both helical transmembrane regions are shaded in tan. K33 and C57 are shown in red. Pathogenic arenaviruses are denoted via **. The prototypic Pichinde virus (PICV) is also shown. Residues with full conservation are indicated by an asterisk (*), whereas those with strongly and weakly similar properties are shown via a semicolon (:) and period (.), respectively. Abbreviations: CHAVB, Chapare virus; DNDV, Dandenong virus; GTOV, Guanarito virus; IPPYV, Ippy virus; LUJOV, Lujo virus; MACV, Machupo virus; MOBV, Mobala virus; MOPV, Mopeia virus; PICV, Pichinde virus; SABV, Sabia virus; WWAV, Whitewater Arroyo virus; ZBD, zinc-binding domain.

Figure 6
Characterization of the SSP and cytoplasmic tail of GP2

(A) Sequence alignment of the LASV GP2 C-terminus of pathogenic and/or OW arenaviruses. Residues in the MPER (purple), TM (shaded black), and cytoplasmic tail implicated in fusion are bolded. The ZBD1 (orange) and ZBD2 (red) are shown. (B) Illustration of the SSP (pink) and its association with the TM (black) of GP2 from the top and side view. Helix 1 (H1) creates an interface with the TM, whereas helix 2 (H2) contains C57, the fourth ligand in ZBD2 (red). ZBD1 (orange) is shown as well. Each ZBD coordinates with a zinc ion (purple) (C) Sequence alignment of the SSP with the myristoylation motif outlined in green. Both helical transmembrane regions are shaded in tan. K33 and C57 are shown in red. Pathogenic arenaviruses are denoted via **. The prototypic Pichinde virus (PICV) is also shown. Residues with full conservation are indicated by an asterisk (*), whereas those with strongly and weakly similar properties are shown via a semicolon (:) and period (.), respectively. Abbreviations: CHAVB, Chapare virus; DNDV, Dandenong virus; GTOV, Guanarito virus; IPPYV, Ippy virus; LUJOV, Lujo virus; MACV, Machupo virus; MOBV, Mobala virus; MOPV, Mopeia virus; PICV, Pichinde virus; SABV, Sabia virus; WWAV, Whitewater Arroyo virus; ZBD, zinc-binding domain.

Close modal

Directly following the MPER lies the TM. Unfortunately, structural characterization of the TM has been challenging—largely due to its hydrophobic nature. Instead, critical residues in the TM have been identified through inhibitor screens. The TM has been shown to have an interaction with the first helix of the SSP, which forms an interface that is often the target of inhibitors and has been proposed to have a role in the pH-sensing mechanism [27–29,39,195]. The mechanism of action behind these inhibitors seems to be the stabilization of the pre-fusion GPC complex via the TM–SSP interface as revealed by inhibition studies [195–197]. The dietary supplement capsaicin [28] and the antifungal isavuconazole [27] were both revealed to target the same three residues in the TM: V431, F434, and V435. Capsaicin and isavuconazole targeted the adjacent region within the N-terminal transmembrane region of the SSP at A25 and S27, respectively. Curiously, the mutation F427I (V435) in the TM of the JUNV GP2 confers immunological resistance to the live-attenuated Candid#1 vaccine [198]. This mutation has an epistatic interaction with a lysine-to-serine mutated residue in the SSP (K33), a residue that is critical for the SSP’s role in pH-sensing [198,199]. These mutations are the sole basis for the vaccine’s attenuation and have thus raised concerns for reversion to the pathogenic phenotype. Regardless, more structural information is necessary to validate this hypothesis. Like the fusion domain, the pre-fusion and post-fusion state of the TM remains to be clarified. Elucidation of this structural information will shed some light on the interactions within the TM-SSP interface and their roles in the functionality of the GP2.

The retention of SSP is dependent not only on its interaction with the TM but the cytoplasmic tail as well. This was inferred as replacement of the TM and cytoplasmic tail with an unrelated sequence impacted SSP association, whereas substitutions elsewhere in the GPC did not [75]. Furthermore, the cytoplasmic tail of JUNV contains six cysteine and histidine residues that are essential for SSP association and form two different zinc-binding domain (ZBD) motifs [200–202]. The first ZBD (ZBD1) is formed by H447 (H455), H449 (H457), and C455 (C463), whereas the second ZBD (ZBD2) is created by H459 (H467), C467 (C475), and C469 (C477) (Figure 6A). These two ZBD motifs are completely conserved across all NW and OW arenaviruses (Figure 6B). Using isothermal titration calorimetry, ZBD1 and a nonconserved H485 were first identified to bind zinc with a dissociation constant (Kd) in the nanomolar range [200,201]. Oddly, H485 is absent from all NW and OW arenaviruses that are not within the same group as JUNV, including LASV (Figure 6B). This lack of H485 raises the postulation of what might complete the tetrahedral structure. Is it water like ZBD2 before the SSP association? Could it be another residue within the SSP, such as C41 which is moderately conserved? Probably not considering mutational analysis revealed H485 was important in the coordination of the JUNV ZBD but was not necessary for the retention of SSP or membrane fusion activity. What about other conserved residues within GP2? Nonetheless, there is no obvious answer to these questions as no other histidine or cysteine residues are strictly conserved across all arenaviruses.

To follow-up, York and colleagues hypothesized that ZBD2 was formed with C57 of the SSP as the fourth ligand (Figure 6C) [201]. Before SSP association, a water molecule acts as a fourth ligand to complete the tetrahedral coordination of zinc. The necessity of these zinc-binding residues was further validated in a separate study on Pichinde virus, a nonpathogenic NW prototypic arenavirus [202]. In the same study, it was found that the fully conserved W503 (W488) was also indispensable for viral replication. Individual mutational studies on all seven of these residues (H447, H449, C455, H459, C467, C469, and W503) resulted in the complete abolishment of SSP association and rendered the GPC inactive [200–202]. It was thus speculated that these residues either facilitate the proper folding of the cytoplasmic tail and its association with the SSP or merely that zinc coordination is required for SSP retention. The rationale for the former will be discussed more in-depth later in this review article.

Altogether, this affirms the characterization of the LASV GP2 as a class one fusion protein as well as highlights some interesting features. Unlike other class one fusion glycoproteins, LASV GP2 contains a noncanonical NFP and IFL that must be characterized further to completely understand their necessity. The TM also requires further experimentation, including structural investigation and functional analysis. Interestingly, multiple inhibitors seem to target the same region (residues 434 to 437) in the TM of various OW and NW arenaviruses. This could potentially be a region of crucial hydrophobic interactions between the TM-SSP interface. Moreover, an investigation is also necessary to fully probe the novel ZBDs, specifically the fourth ligand of ZBD1 in LASV and other arenaviruses. Other future directions will likely include characterizing the exact role of the MPER, how the GP2 coordinates with the SSP, and any conformational changes that are undergone during the fusion process.

Unusual retention of the SSP in the mature GPC

Although the structural changes undergone by the LASV GPC during membrane fusion follow the same framework as other class one fusion proteins, the pH-induced activation in the late endosome is distinct—in part due to the unusual retention of the SSP in the mature GPC and its involvement in pH sensing. Conventional signal peptides are 18–30-amino acid peptides and are responsible for directing proteins to the proper intra- and/or extracellular location [203–207]. After successful translocation, the signaling peptide is cleaved and degraded. They usually contain a positively charged N-terminus, central hydrophobic region, and polar C-terminus [208,209]. On the contrary, the LASV SSP is abnormally long at 58 amino acids and spans from M1 to T58 of the mature GPC (Figure 6C). It is proposed to traverse the membrane twice with two distinct hydrophobic domains: helix 1 (H1, E17–L32) and helix 2 (H2, C41–G54). These helices have an antiparallel orientation and are connected by an eight amino acid ectodomain [89–91,199,210–213]. The N- and C-termini extend from M1–E16 and R55–T58, respectively, and reside in the cytosol [91,199].

Co-immunoprecipitation experiments have also demonstrated that the LASV SSP was retained in the mature GPC—a feature that is unique to arenaviruses [73,107,199]. After SPase cleavage, the SSP remains noncovalently associated with the GPC complex via the TM and ZBD2 [90,91,196,200,201]. Confocal microscopy studies on JUNV have demonstrated that the SSP is required for translocation of the GP1 and GP2 to the Golgi apparatus [212]. When the SSP was replaced with a traditional signal peptide or altogether absent, the GPC precursor was retained within the ER and was not processed or functional [73–75,89,214,215]. Therefore, not only is the SSP unusually retained in the mature form of the GPC, but it is also an integral third subunit required for the proper maturation of GPC.

While the LASV SSP maintains the conventional role of a signal peptide for intracellular trafficking, it also has a role in the LASV pH-dependent fusion process. The association of the SSP with GP2 throughout membrane fusion has been shown to influence the pH-sensing mechanism and stabilize the intermediate conformation of GP2 [197]. More specifically, the highly conserved K33 within the SSP has been shown to be required for fusion activity of the GPC. When this residue was substituted for alanine, fusion was not observed, likely due to a complete loss of fusogenicity. Substitutions that reduced positive polarity, such as K33R, K33H, and K33Q, increased the threshold pH for fusion such that optimal pH was less acidic [196]. Intriguingly, K33 is located within the short ectodomain loop that links the two transmembrane helices of the SSP (Figure 6B,C) [75]. We postulate that this location positions K33 at a key location in the extracellular environment for sensing pH alterations and/or forming an intersubunit salt bridge with GP2.

The pH-sensing mechanism also seems to be influenced by ZBD2. As mentioned previously, four residues comprise the novel ZBD2 (C57, H459, C467, and C469)—one of which, C57, is located within the SSP [201]. This cysteine is invariable across all arenaviruses whereas residues flanking it are variable (Figure 6C) [90,201]. The variable residues are important for SPase cleavage and GPC maturation but are not responsible for SSP retention, whereas C57 has been shown to have roles in SSP retention [90,199]. Mutation at C57 resulted in the complete abolishment of SSP association with GP2 [200]. It could be speculated that zinc is required for SSP retention and the loss of the intersubunit ZBD hinders this coordination. However, other studies have shown that proper C57 placement is promoted by the N-terminal region of the SSP or transmembrane regions of the GP2 [212]. Thus, it is more so likely that ZBD2 coordinates with C57 to retain and position the ectodomain loop of the SSP appropriately [200–202].

Another unusual property is that the SSP is myristoylated at a conserved N-terminal myristoylation motif, specifically G2–T6 [73]. Myristoylation has been demonstrated to be an important modification for the viral lifecycle, membrane targeting, and conformational stability [216–225]. In the case of the LASV SSP, a point mutation to alanine at G2 resulted in a significant hindrance of membrane fusion activity while GPC assembly was unaffected [91,226,227]. Previous studies have also demonstrated that myristoylation does not appear to affect SSP retention, either. The mechanism of action behind this motif is unclear but has been suggested to function late in the fusion process to promote the merging of the membranes [227].

Overall, these studies have suggested the LASV SSP has multiple unique properties when compared with other class one fusion proteins and signal peptides. Based on the lack of GPC processing in the absence of SSP, it is evident that SSP retention is required for proper GPC maturation. Aside from this, however, there is an extensive knowledge gap surrounding the LASV SSP. Given its unusual retention in the mature form, it is difficult to draw direct comparisons to other class one fusion proteins. As a result, the structural and functional characteristics remain poorly understood. The identification of an intersubunit ZBD that is coordinated with C57 of the SSP and the ability of K33 to sense pH, both by coordinating with GP2, provides an interesting starting point for future experimentation. Based on the location of these residues, it seems a detailed understanding of the localized interactions between the SSP and GP2 will provide key insights into the unique function of SSP. Specific investigation into the role of myristoylation is also required. Together, these insights will improve our knowledge surrounding the unusual retention of the SSP, which may be helpful in the development of new therapeutics as multiple inhibitors seem to target the GP2–SSP interface.

Despite LASV being the most prevalent arenavirus afflicting humans, there are limited treatment options due to a lack of structural and functional information. The GPC is the only protein located on the virion surface of the LASV particle and has a vital role in the virus’ lifecycle, which makes it an exciting target for drug development. In other class one fusion proteins, the incorporation of the viral particle is dependent on an interplay of interactions between the matrix protein and glycoprotein. However, before this can be fully understood in LASV, fundamental questions about the LASV GPC and the unique properties of its components must be answered. First, the molecular mechanism by which the glycosylated GP1 manages to evade antibody-mediated immune responses must be understood. The receptor switch by GP1 is also unique; thus, a deeper understanding of the residues involved in the receptor switch mechanism should be completed. The most extensive knowledge gap involves the LASV GP2 and SSP. Further experimentation must be completed on the fusion domain to dissect the requirement of two fusion proteins by LASV to facilitate fusion efficiently. Moreover, the structural features of the GP2 and SSP interaction, specifically the TM–SSP interface and novel ZBDs, must be addressed. Following this, the molecular mechanism by which the GP2 and SSP sense pH changes to promote membrane fusion should be elucidated. In terms of the SSP alone, the role of its myristoylation requires further investigation. Ultimately, these experiments will provide fundamental information for novel targets that will be instrumental in drug design against LASV.

The authors declare that there are no competing interests associated with the manuscript.

We would like to thank the entire Lee lab for their continual advice, support, and encouragement in constructing this manuscript.

     
  • αDG

    α-dystroglycan

  •  
  • 6HB

    six-helix bundle

  •  
  • CFR

    case fatality rate

  •  
  • CHAVB

    Chapare virus

  •  
  • DNDV

    Dandenong virus

  •  
  • EBOV

    Ebola virus

  •  
  • GP1

    glycoprotein 1

  •  
  • GP2

    glycoprotein 2

  •  
  • GPC

    glycoprotein complex

  •  
  • GTOV

    Guanarito virus

  •  
  • HIV

    human immunodeficiency virus

  •  
  • HR1

    heptad repeat 1

  •  
  • HR2

    heptad repeat 2

  •  
  • IFL

    internal fusion loop

  •  
  • IPPYV

    Ippy virus

  •  
  • JUNV

    Junín virus

  •  
  • LAMP1

    lysosomal-associated membrane protein 1

  •  
  • LASV

    Lassa virus

  •  
  • LCMV

    lymphocytic choriomeningitis virus

  •  
  • LUJOV

    Lujo virus

  •  
  • MACV

    Machupo virus

  •  
  • MOBV

    Mobala virus

  •  
  • MOPV

    Mopeia virus

  •  
  • MPER

    membrane proximal external region

  •  
  • NFP

    N-terminal fusion peptide

  •  
  • NHE

    sodium hydrogen exchanger

  •  
  • NW

    New-World arenavirus

  •  
  • OW

    Old-World arenavirus

  •  
  • PICV

    Pichinde virus

  •  
  • RBD1

    receptor-binding domain 1

  •  
  • RBD2

    receptor-binding domain 2

  •  
  • SABV

    Sabia virus

  •  
  • SARS-CoV-2

    severe acute respiratory syndrome coronavirus 2

  •  
  • SPase

    cellular signal peptidase

  •  
  • SSP

    stable signal peptide

  •  
  • TAM

    Tyro3/Axl/Mer

  •  
  • TM

    transmembrane domain

  •  
  • WWAV

    Whitewater Arroyo virus

  •  
  • ZBD

    zinc-binding domain

1.
Radoshitzky
S.R.
,
Bào
Y.
,
Buchmeier
M.J.
,
Charrel
R.N.
,
Clawson
A.N.
,
Clegg
C.S.
et al.
(
2015
)
Past, present, and future of arenavirus taxonomy
.
Arch. Virol.
160
,
1851
1874
[PubMed]
2.
McLay
L.
,
Liang
Y.
and
Ly
H.
(
2014
)
Comparative analysis of disease pathogenesis and molecular mechanisms of New World and Old World arenavirus infections
.
J. Gen. Virol.
95
,
1
15
[PubMed]
3.
Yun
N.E.
and
Walker
D.H.
(
2012
)
Pathogenesis of Lassa fever
.
Viruses
4
,
2031
2048
[PubMed]
4.
Charrel
R.N.
and
de Lamballerie
X.
(
2010
)
Zoonotic aspects of arenavirus infections
.
Vet. Microbiol.
140
,
213
220
[PubMed]
5.
McCormick
J.B.
and
Fisher-Hoch
S.P.
(
2002
)
Lassa fever
.
Curr. Top. Microbiol. Immunol.
262
,
75
109
[PubMed]
6.
Rojek
J.M.
,
Sanchez
A.B.
,
Nguyen
N.T.
,
de la Torre
J.-C.
and
Kunz
S.
(
2008
)
Different mechanisms of cell entry by human-pathogenic old world and new world arenaviruses
.
J. Virol.
82
,
7677
7687
[PubMed]
7.
Lecompte
E.
,
Fichet-Calvet
E.
,
Daffis
S.
,
Koulémou
K.
,
Sylla
O.
,
Kourouma
F.
et al.
(
2006
)
Mastomys natalensis and Lassa fever, West Africa
.
Emerg. Infect. Dis.
12
,
1971
1974
[PubMed]
8.
Woyessa
A.B.
,
Maximore
L.
,
Keller
D.
,
Dogba
J.
,
Pajibo
M.
,
Johnson
K.
et al.
(
2019
)
Lesson learned from the investigation and response of Lassa fever outbreak, Margibi County, Liberia, 2018: case report
.
BioMed Central Infect. Dis.
19
,
610
9.
Willard
K.A.
,
Alston
J.T.
,
Acciani
M.
and
Brindley
M.A.
(
2019
)
Identification of residues in Lassa virus glycoprotein subunit 2 that are critical for protein function
.
Pathogens
8
,
1
13
10.
McCormick
J.B.
,
Webb
P.A.
,
Krebs
J.W.
,
Johnson
K.M.
and
Smith
E.S.
(
1987
)
A prospective study of the epidemiology and ecology of Lassa fever
.
J. Infect. Dis.
135
,
437
444
11.
Centers for Disease Control and Prevention
(
2019
)
Lassa Fever [Fact Sheet]
.
https://www.cdc.gov/vhf/lassa/pdf/factsheet.pdf
12.
World Health Organization
. (
2017
)
Lassa fever fact sheet [press release]
.
https://www.who.int/news-room/fact-sheets/detail/lassa-fever
13.
Herring
S.
,
Oda
J.M.
,
Wagoner
J.
,
Kirchmeier
D.
,
O’Connor
A.
,
Nelson
E.A.
et al.
(
2021
)
Inhibition of arenaviruses by combinations of orally available approved drugs
.
Antimicrob. Agents Chemother.
65
,
1
17
14.
Richmond
J.K.
and
Baglole
D.J.
(
2003
)
Lassa fever: epidemiology, clinical features, and social consequences
.
Br. Med. J.
327
,
1271
1275
15.
Safronetz
D.
,
Lopez
J.E.
,
Sogoba
N.
,
Traore
S.F.
,
Raffel
S.J.
,
Fischer
E.R.
et al.
(
2010
)
Detection of Lassa virus, Mali
.
Emerg. Infect. Dis.
16
,
1123
1126
[PubMed]
16.
Nigeria Centre for Disease Control
. (
2021
)
Lassa Fever Situation Report [press release]
.
https://ncdc.gov.ng/diseases/sitreps/?cat=5&name=An%20update%20of%20Lassa%20fever%20outbreak%20in%20Nigeria
17.
Yaro
C.A.
,
Kogi
E.
,
Opara
K.N.
,
Batiha
G.E.
,
Baty
R.S.
,
Albrakati
A.
et al.
(
2021
)
Infection pattern, case fatality rate and spread of Lassa virus in Nigeria
.
BMC Infect. Dis.
21
,
149
[PubMed]
18.
Bagcchi
S.
(
2020
)
Lassa fever outbreak continues across Nigeria
.
Lancet Infect. Dis.
20
,
543
[PubMed]
19.
McCormick
J.B.
(
1986
)
Clinical, epidemiologic, and therapeutic aspects of Lassa fever
.
Med. Microbiol. Immunol.
175
,
153
155
[PubMed]
20.
Barbuddhe
S.B.
,
Rawool
D.B.
,
Gaonkar
P.P.
,
Vergis
J.
,
Dhama
K.
and
Malik
S.S.
(
2020
)
Global scenario, public health concerns and mitigation strategies to counter current ongoing SARS-CoV-2/COVID-19 pandemic
.
Hum. Vaccin. Immunother.
16
,
3023
3033
[PubMed]
21.
Mallah
S.I.
,
Ghorab
O.K.
,
Al-Salmi
S.
,
Abdellatif
O.S.
,
Tharmaratnam
T.
,
Iskandar
M.A.
et al.
(
2021
)
COVID-19: breaking down a global health crisis
.
Ann. Clin. Microbiol. Antimicrob.
20
,
1
35
22.
Van Damme
W.
,
Dahake
R.
,
Delamou
A.
,
Ingelbeen
B.
,
Wouters
E.
,
Vanham
G.
et al.
(
2020
)
The COVID-19 pandemic: diverse contexts; different epidemics-how and why?
Br. Med. J. Glob. Health
5
,
1
16
23.
Kumar
A.
,
Singh
R.
,
Kaur
J.
,
Pandey
S.
,
Sharma
V.
,
Thakur
L.
et al.
(
2021
)
Wuhan to world: the COVID-19 pandemic
.
Front. Cell. Infect. Microbiol.
11
,
1
21
24.
Chams
N.
,
Chams
S.
,
Badran
R.
,
Shams
A.
,
Araji
A.
,
Raad
M.
et al.
(
2020
)
COVID-19: a multidisciplinary review
.
Front. Public Health
8
,
1
20
[PubMed]
25.
Fadaka
A.O.
,
Sibuyi
N.R.S.
,
Adewale
O.B.
,
Bakare
O.O.
,
Akanbi
M.O.
,
Klein
A.
et al.
(
2020
)
Understanding the epidemiology, pathophysiology, diagnosis and management of SARS-CoV-2
.
J. Int. Med. Res.
48
,
1
23
26.
Hansen
F.
,
Jarvis
M.A.
,
Feldmann
H.
and
Rosenke
K.
(
2021
)
Lassa virus treatment options
.
Microorganisms
9
,
1
16
27.
Zhang
X.
,
Tang
K.
and
Guo
Y.
(
2020
)
The antifungal isavuconazole inhibits the entry of lassa virus by targeting the stable signal peptide-GP2 subunit interface of lassa virus glycoprotein
.
Antiviral Res.
174
,
104701
[PubMed]
28.
Tang
K.
,
Zhang
X.
and
Guo
Y.
(
2020
)
Identification of the dietary supplement capsaicin as an inhibitor of Lassa virus entry
.
Acta Pharm. Sin. B
10
,
789
798
[PubMed]
29.
Wang
P.
,
Liu
Y.
,
Zhang
G.
,
Wang
S.
,
Guo
J.
,
Cao
J.
et al.
(
2018
)
Screening and identification of Lassa virus entry inhibitors from an FDA-approved drug library
.
J. Virol.
92
,
1
14
30.
Hansen
F.
,
Jarvis
M.A.
,
Feldmann
H.
and
Rosenke
K.
(
2021
)
Lassa virus treatment options
.
Microorganisms
9
,
772
,
[PubMed]
31.
McCormick
J.B.
,
King
I.J.
,
Webb
P.A.
,
Scribner
C.L.
,
Craven
R.B.
,
Johnson
K.M.
et al.
(
1986
)
Lassa fever. Effective therapy with ribavirin
.
N. Engl. J. Med.
314
,
20
26
[PubMed]
32.
Eberhardt
K.A.
,
Mischlinger
J.
,
Jordan
S.
,
Groger
M.
,
Günther
S.
and
Ramharter
M.
(
2019
)
Ribavirin for the treatment of Lassa fever: a systematic review and meta-analysis
.
Int. J. Infect. Dis.
87
,
15
20
[PubMed]
33.
Bolken
T.C.
,
Laquerre
S.
,
Zhang
Y.
,
Bailey
T.R.
,
Pevear
D.C.
,
Kickner
S.S.
et al.
(
2006
)
Identification and characterization of potent small molecule inhibitor of hemorrhagic fever New World arenaviruses
.
Antiviral Res.
69
,
86
97
[PubMed]
34.
Larson
R.A.
,
Dai
D.
,
Hosack
V.T.
,
Tan
Y.
,
Bolken
T.C.
,
Hruby
D.E.
et al.
(
2008
)
Identification of a broad-spectrum arenavirus entry inhibitor
.
J. Virol.
82
,
10768
10775
[PubMed]
35.
Lee
A.M.
,
Rojek
J.M.
,
Spiropoulou
C.F.
,
Gundersen
A.T.
,
Jin
W.
,
Shaginian
A.
et al.
(
2008
)
Unique small molecule entry inhibitors of hemorrhagic fever arenaviruses
.
J. Biol. Chem.
283
,
18734
18742
[PubMed]
36.
Shankar
S.
,
Whitby
L.R.
,
Casquilho-Gray
H.E.
,
York
J.
,
Boger
D.L.
and
Nunberg
J.H.
(
2016
)
Small-molecule fusion inhibitors bind the pH-sensing stable signal peptide-GP2 subunit interface of the Lassa virus envelope glycoprotein
.
J. Virol.
90
,
6799
6807
[PubMed]
37.
Cashman
K.A.
,
Smith
M.A.
,
Twenhafel
N.A.
,
Larson
R.A.
,
Jones
K.F.
,
Allen
R.D.
III
et al.
(
2011
)
Evaluation of Lassa antiviral compound ST-193 in a guinea pig model
.
Antiviral Res.
90
,
70
79
[PubMed]
38.
Zhang
X.
,
Yan
F.
,
Tang
K.
,
Chen
Q.
,
Guo
J.
,
Zhu
W.
et al.
(
2019
)
Identification of a clinical compound losmapimod that blocks Lassa virus entry
.
Antiviral Res.
167
,
68
77
[PubMed]
39.
Ngo
N.
,
Henthorn
K.S.
,
Cisneros
M.I.
,
Cubitt
B.
,
Iwasaki
M.
,
de la Torre
J.C.
et al.
(
2015
)
Identification and mechanism of action of a novel small-molecule inhibitor of arenavirus multiplication
.
J. Virol.
89
,
10924
10933
[PubMed]
40.
Hulseberg
C.E.
,
Fénéant
L.
,
Szymańska-de Wijs
K.M.
,
Kessler
N.P.
,
Nelson
E.A.
,
Shoemaker
C.J.
et al.
(
2019
)
Arbidol and other low-molecular-weight drugs that inhibit Lassa and Ebola viruses
.
J. Virol.
93
,
1
19
41.
Torriani
G.
,
Trofimenko
E.
,
Mayor
J.
,
Fedeli
C.
,
Moreno
H.
,
Michel
S.
et al.
(
2019
)
Identification of clotrimazole derivatives as specific inhibitors of arenavirus fusion
.
J. Virol.
93
,
1
19
42.
Gowen
B.B.
,
Hickerson
B.T.
,
York
J.
,
Westover
J.B.
,
Sefing
E.J.
,
Bailey
K.W.
et al.
(
2021
)
Second-generation live-attenuated Candid#1 vaccine virus resists reversion and protects against lethal Junín virus infection in guinea pigs
.
J. Virol.
95
,
e0039721
[PubMed]
43.
Albariño
C.G.
,
Bird
B.H.
,
Chakrabarti
A.K.
,
Dodd
K.A.
,
Flint
M.
,
Bergeron
E.
et al.
(
2011
)
The major determinant of attenuation in mice of the Candid1 vaccine for Argentine hemorrhagic fever is located in the G2 glycoprotein transmembrane domain
.
J. Virol.
85
,
10404
10408
[PubMed]
44.
McKee
K.T.
Jr
,
Oro
J.G.
,
Kuehne
A.I.
,
Spisso
J.A.
and
Mahlandt
B.G.
(
1992
)
Candid No. 1 Argentine hemorrhagic fever vaccine protects against lethal Junin virus challenge in rhesus macaques
.
Intervirology
34
,
154
163
[PubMed]
45.
Enria
D.A.
,
Ambrosio
A.M.
,
Briggiler
A.M.
,
Feuillade
M.R.
and
Crivelli
E.
(
2010
)
[Candid#1 vaccine against Argentine hemorrhagic fever produced in Argentina. Immunogenicity and safety]
.
Medicina (B. Aires)
70
,
215
222
[PubMed]
46.
Enria
D.A.
and
Barrera Oro
J.G.
(
2002
)
Junin virus vaccines
.
Curr. Top. Microbiol. Immunol.
263
,
239
261
[PubMed]
47.
McKee
K.T.
Jr
,
Oro
J.G.
,
Kuehne
A.I.
,
Spisso
J.A.
and
Mahlandt
B.G.
(
1993
)
Safety and immunogenicity of a live-attenuated Junin (Argentine hemorrhagic fever) vaccine in rhesus macaques
.
Am. J. Trop. Med. Hyg.
48
,
403
411
[PubMed]
48.
Maiztegui
J.I.
,
McKee
K.T.
Jr
,
Barrera Oro
J.G.
,
Harrison
L.H.
,
Gibbs
P.H.
,
Feuillade
M.R.
et al.
(
1998
)
Protective efficacy of a live attenuated vaccine against Argentine hemorrhagic fever. AHF Study Group
.
J. Infect. Dis.
177
,
277
283
[PubMed]
49.
Martinez-Sobrido
L.
and
de la Torre
J.C.
(
2016
)
Novel strategies for development of hemorrhagic fever arenavirus live-attenuated vaccines
.
Expert Rev. Vaccines
15
,
1113
1121
[PubMed]
50.
Sommerstein
R.
,
Flatz
L.
,
Remy
M.M.
,
Malinge
P.
,
Magistrelli
G.
,
Fischer
N.
et al.
(
2015
)
Arenavirus glycan shield promotes neutralizing antibody evasion and protracted infection
.
PLoS Pathog.
11
,
e1005276
[PubMed]
51.
Watanabe
Y.
,
Raghwani
J.
,
Allen
J.D.
,
Seabright
G.E.
,
Li
S.
,
Moser
F.
et al.
(
2018
)
Structure of the Lassa virus glycan shield provides a model for immunological resistance
.
Proc. Natl. Acad. Sci. U.S.A.
115
,
7320
7325
[PubMed]
52.
Koma
T.
,
Huang
C.
,
Coscia
A.
,
Hallam
S.
,
Manning
J.T.
,
Maruyama
J.
et al.
(
2021
)
Glycoprotein N-linked glycans play a critical role in arenavirus pathogenicity
.
PLoS Pathog.
17
,
e1009356
[PubMed]
53.
Zhu
X.
,
Liu
Y.
,
Guo
J.
,
Cao
J.
,
Wang
Z.
,
Xiao
G.
et al.
(
2021
)
Effects of N-linked glycan on Lassa virus envelope glycoprotein cleavage, infectivity, and immune response
.
Virol. Sin.
36
,
774
783
[PubMed]
54.
Galan-Navarro
C.
,
Rincon-Restrepo
M.
,
Zimmer
G.
,
Ollmann Saphire
E.
,
Hubbell
J.A.
,
Hirosue
S.
et al.
(
2017
)
Oxidation-sensitive polymersomes as vaccine nanocarriers enhance humoral responses against Lassa virus envelope glycoprotein
.
Virology
512
,
161
171
[PubMed]
55.
Borio
L.
,
Inglesby
T.
,
Peters
C.J.
,
Schmaljohn
A.L.
,
Hughes
J.M.
,
Jahrling
P.B.
et al.
(
2002
)
Hemorrhagic fever viruses as biological weapons: medical and public health management
.
JAMA
287
,
2391
2405
[PubMed]
56.
World Health Organization
. (
2021
)
Prioritizing diseases for research and development in emergency contexts
[press release]
,
https://www.who.int/activities/prioritizing-diseases-for-research-and-development-in-emergency-contexts
57.
Mehand
M.S.
,
Al-Shorbaji
F.
,
Millett
P.
and
Murgue
B.
(
2018
)
The WHO R&D Blueprint: 2018 review of emerging infectious diseases requiring urgent research and development efforts
.
Antiviral Res.
159
,
63
67
[PubMed]
58.
Hughson
F.M.
(
1995
)
Structural characterization of viral fusion proteins
.
Curr. Biol.
5
,
265
274
[PubMed]
59.
Eschli
B.
,
Quirin
K.
,
Wepf
A.
,
Weber
J.
,
Zinkernagel
R.
and
Hengartner
H.
(
2006
)
Identification of an N-terminal trimeric coiled-coil core within arenavirus glycoprotein 2 permits assignment to class I viral fusion proteins
.
J. Virol.
80
,
5897
5907
[PubMed]
60.
White
J.M.
,
Delos
S.E.
,
Brecher
M.
and
Schornberg
K.
(
2008
)
Structures and mechanisms of viral membrane fusion proteins: multiple variations on a common theme
.
Crit. Rev. Biochem. Mol. Biol.
43
,
189
219
[PubMed]
61.
Kielian
M.
and
Rey
F.A.
(
2006
)
Virus membrane-fusion proteins: more than one way to make a hairpin
.
Nat. Rev. Microbiol.
4
,
67
76
[PubMed]
62.
Wang
W.
,
Zhou
Z.
,
Zhang
L.
,
Wang
S.
and
Xiao
G.
(
2016
)
Structure-function relationship of the mammarenavirus envelope glycoprotein
.
Virol. Sin.
31
,
380
394
[PubMed]
63.
Wilson
I.A.
,
Skehel
J.J.
and
Wiley
D.C.
(
1981
)
Structure of the haemagglutinin membrane glycoprotein of influenza virus at 3 A resolution
.
Nature
289
,
366
373
[PubMed]
64.
Dimitrov
A.S.
,
Rawat
S.S.
,
Jiang
S.
and
Blumenthal
R.
(
2003
)
Role of the fusion peptide and membrane-proximal domain in HIV-1 envelope glycoprotein-mediated membrane fusion
.
Biochemistry
42
,
14150
14158
[PubMed]
65.
Zhu
J.
,
Xiao
G.
,
Xu
Y.
,
Yuan
F.
,
Zheng
C.
,
Liu
Y.
et al.
(
2004
)
Following the rule: formation of the 6-helix bundle of the fusion core from severe acute respiratory syndrome coronavirus spike protein and identification of potent peptide inhibitors
.
Biochem. Biophys. Res. Commun.
319
,
283
288
[PubMed]
66.
White
J.
and
Whittaker
G.
(
2016
)
Fusion of enveloped viruses in endosomes
.
Traffic
17
,
593
614
[PubMed]
67.
Leikin
S.
,
Parsegian
V.A.
,
Rau
D.C.
and
Rand
R.P.
(
1993
)
Hydration forces
.
Annu. Rev. Phys. Chem.
44
,
369
395
[PubMed]
68.
Bentz
J.
,
Ellens
H.
and
Alford
D.
(
1990
)
An architecture for the fusion site of influenza hemagglutinin
.
FEBS Lett.
276
,
1
5
69.
Helm
C.A.
,
Israelachvili
J.N.
and
McGuiggan
P.M.
(
1989
)
Molecular mechanisms and forces involved in the adhesion and fusion of amphiphilic bilayers
.
Science
246
,
919
922
[PubMed]
70.
Harrison
S.C.
(
2015
)
Viral membrane fusion
.
Virology
479–480
,
498
507
[PubMed]
71.
Hastie
K.M.
,
Zandonatti
M.A.
,
Kleinfelter
L.M.
,
Heinrich
M.L.
,
Rowland
M.M.
,
Chandran
K.
et al.
(
2017
)
Structural basis for antibody-mediated neutralization of Lassa virus
.
Science
356
,
923
[PubMed]
72.
Borrow
P.
and
Oldstone
M.B.
(
1992
)
Characterization of lymphocytic choriomeningitis virus-binding protein(s): a candidate cellular receptor for the virus
.
J. Virol.
66
,
7270
7281
[PubMed]
73.
York
J.
,
Romanowski
V.
,
Lu
M.
and
Nunberg
J.H.
(
2004
)
The signal peptide of the Junín arenavirus envelope glycoprotein is myristoylated and forms an essential subunit of the mature G1-G2 complex
.
J. Virol.
78
,
10783
10792
[PubMed]
74.
Eichler
R.
,
Lenz
O.
,
Strecker
T.
,
Eickmann
M.
,
Klenk
H.D.
and
Garten
W.
(
2003
)
Identification of Lassa virus glycoprotein signal peptide as a trans-acting maturation factor
.
EMBO Rep.
4
,
1084
1088
[PubMed]
75.
Agnihothram
S.S.
,
York
J.
and
Nunberg
J.H.
(
2006
)
Role of the stable signal peptide and cytoplasmic domain of G2 in regulating intracellular transport of the Junín virus envelope glycoprotein complex
.
J. Virol.
80
,
5189
5198
[PubMed]
76.
Pasqual
G.
,
Rojek
J.M.
,
Masin
M.
,
Chatton
J.Y.
and
Kunz
S.
(
2011
)
Old world arenaviruses enter the host cell via the multivesicular body and depend on the endosomal sorting complex required for transport
.
PLoS Pathog.
7
,
e1002232
77.
Di Simone
C.
,
Zandonatti
M.A.
and
Buchmeier
M.J.
(
1994
)
Acidic pH triggers LCMV membrane fusion activity and conformational change in the glycoprotein spike
.
Virology
198
,
455
465
[PubMed]
78.
Jae
L.T.
,
Raaben
M.
,
Herbert
A.S.
,
Kuehne
A.I.
,
Wirchnianski
A.S.
,
Soh
T.K.
et al.
(
2014
)
Lassa virus entry requires a trigger-induced receptor switch
.
Science
344
,
1506
1510
[PubMed]
79.
Hulseberg
C.E.
,
Fénéant
L.
,
Szymańska
K.M.
and
White
J.M.
(
2018
)
Lamp1 increases the efficiency of Lassa virus infection by promoting fusion in less acidic endosomal compartments
.
Am. Soc. Microbiol.
9
,
1
14
80.
Li
S.
,
Sun
Z.
,
Pryce
R.
,
Parsy
M.-L.
,
Fehling
S.K.
,
Schlie
K.
et al.
(
2016
)
Acidic pH-induced conformations and LAMP1 binding of the Lassa virus glycoprotein spike
.
PLoS Pathogens
12
,
2161
2181
81.
Igonet
S.
,
Vaney
M.C.
,
Vonrhein
C.
,
Bricogne
G.
,
Stura
E.A.
,
Hengartner
H.
et al.
(
2011
)
X-ray structure of the arenavirus glycoprotein GP2 in its postfusion hairpin conformation
.
Proc. Natl. Acad. Sci. U.S.A.
108
,
19967
19972
[PubMed]
82.
Urata
S.
and
Yasuda
J.
(
2012
)
Molecular mechanism of arenavirus assembly and budding
.
Viruses
4
,
2049
2079
[PubMed]
83.
Birtles
D.
and
Lee
J.
(
2021
)
Identifying distinct structural features of the SARS-CoV-2 spike protein fusion domain essential for membrane interaction
.
Biochemistry
60
,
2978
2986
[PubMed]
84.
Khelashvili
G.
,
Plante
A.
,
Doktorova
M.
and
Weinstein
H.
(
2021
)
Ca(2+)-dependent mechanism of membrane insertion and destabilization by the SARS-CoV-2 fusion peptide
.
Biophys. J.
120
,
1105
1119
[PubMed]
85.
Madu
I.G.
,
Roth
S.L.
,
Belouzard
S.
and
Whittaker
G.R.
(
2009
)
Characterization of a highly conserved domain within the severe acute respiratory syndrome coronavirus spike protein S2 domain with characteristics of a viral fusion peptide
.
J. Virol.
83
,
7411
7421
[PubMed]
86.
Lai
A.L.
,
Millet
J.K.
,
Daniel
S.
,
Freed
J.H.
and
Whittaker
G.R.
(
2017
)
The SARS-CoV fusion peptide forms an extended bipartite fusion platform that perturbs membrane order in a calcium-dependent manner
.
J. Mol. Biol.
429
,
3875
3892
[PubMed]
87.
Koppisetti
R.K.
,
Fulcher
Y.G.
and
Van Doren
S.R.
(
2021
)
Fusion peptide of SARS-CoV-2 spike rearranges into a wedge inserted in bilayered micelles
.
J. Am. Chem. Soc.
143
,
13205
13211
[PubMed]
88.
Lai
A.L.
and
Freed
J.H.
(
2021
)
SARS-CoV-2 fusion peptide has a greater membrane perturbating effect than SARS-CoV with highly specific dependence on Ca(2)
.
J. Mol. Biol.
433
,
166946
[PubMed]
89.
Eichler
R.
,
Lenz
O.
,
Strecker
T.
and
Garten
W.
(
2003
)
Signal peptide of Lassa virus glycoprotein GP-C exhibits an unusual length
.
FEBS Lett.
538
,
203
206
90.
York
J.
and
Nunberg
J.H.
(
2007
)
Distinct requirements for signal peptidase processing and function in the stable signal peptide subunit of the Junín virus envelope glycoprotein
.
Virology
359
,
72
81
[PubMed]
91.
Saunders
A.A.
,
Ting
J.P.
,
Meisner
J.
,
Neuman
B.W.
,
Perez
M.
,
de la Torre
J.C.
et al.
(
2007
)
Mapping the landscape of the lymphocytic choriomeningitis virus stable signal peptide reveals novel functional domains
.
J. Virol.
81
,
5649
5657
[PubMed]
92.
Shao
J.
,
Liang
Y.
and
Ly
H.
(
2015
)
Human hemorrhagic Fever causing arenaviruses: molecular mechanisms contributing to virus virulence and disease pathogenesis
.
Pathogens
4
,
283
306
[PubMed]
93.
Emonet
S.E.
,
Urata
S.
and
de la Torre
J.C.
(
2011
)
Arenavirus reverse genetics: new approaches for the investigation of arenavirus biology and development of antiviral strategies
.
Virology
411
,
416
425
[PubMed]
94.
Richmond
J.K.
and
Baglole
D.J.
(
2003
)
Lassa fever: epidemiology, clinical features, and social consequences
.
BMJ
327
,
1271
1275
[PubMed]
95.
Hastie
K.M.
and
Saphire
E.O.
(
2018
)
Lassa virus glycoprotein: stopping a moving target
.
Curr. Opin. Virol.
31
,
52
58
[PubMed]
96.
Nunberg
J.H.
and
York
J.
(
2012
)
The curious case of arenavirus entry, and its inhibition
.
Viruses
4
,
83
101
[PubMed]
97.
Olschläger
S.
and
Flatz
L.
(
2013
)
Vaccination strategies against highly pathogenic arenaviruses: the next steps toward clinical trials
.
PLoS Pathog.
9
,
e1003212
[PubMed]
98.
Ibukun
F.I.
(
2020
)
Inter-lineage variation of Lassa virus glycoprotein epitopes: a challenge to Lassa virus vaccine development
.
Viruses
12
,
386
,
[PubMed]
99.
Eichler
R.
,
Lenz
O.
,
Garten
W.
and
Strecker
T.
(
2006
)
The role of single N-glycans in proteolytic processing and cell surface transport of the Lassa virus glycoprotein GP-C
.
Virol J.
3
,
41
[PubMed]
100.
Schwarz
F.
and
Aebi
M.
(
2011
)
Mechanisms and principles of N-linked protein glycosylation
.
Curr. Opin. Struct. Biol.
21
,
576
582
[PubMed]
101.
Bonhomme
C.J.
,
Knopp
K.A.
,
Bederka
L.H.
,
Angelini
M.M.
and
Buchmeier
M.J.
(
2013
)
LCMV glycosylation modulates viral fitness and cell tropism
.
PLoS ONE
8
,
e53273
[PubMed]
102.
Bowden
T.A.
,
Crispin
M.
,
Graham
S.C.
,
Harvey
D.J.
,
Grimes
J.M.
,
Jones
E.Y.
et al.
(
2009
)
Unusual molecular architecture of the machupo virus attachment glycoprotein
.
J. Virol.
83
,
8259
8265
[PubMed]
103.
Beyer
W.R.
,
Pöpplau
D.
,
Garten
W.
,
von Laer
D.
and
Lenz
O.
(
2003
)
Endoproteolytic processing of the lymphocytic choriomeningitis virus glycoprotein by the subtilase SKI-1/S1P
.
J. Virol.
77
,
2866
2872
[PubMed]
104.
Lenz
O.
,
ter Meulen
J.
,
Klenk
H.D.
,
Seidah
N.G.
and
Garten
W.
(
2001
)
The Lassa virus glycoprotein precursor GP-C is proteolytically processed by subtilase SKI-1/S1P
.
Proc. Natl. Acad. Sci. U.S.A.
98
,
12701
12705
[PubMed]
105.
Rojek
J.M.
,
Lee
A.M.
,
Nguyen
N.
,
Spiropoulou
C.F.
and
Kunz
S.
(
2008
)
Site 1 protease is required for proteolytic processing of the glycoproteins of the South American hemorrhagic fever viruses Junin, Machupo, and Guanarito
.
J. Virol.
82
,
6045
6051
[PubMed]
106.
Burri
D.J.
,
Pasquato
A.
,
da Palma
J.R.
,
Igonet
S.
,
Oldstone
M.B.
and
Kunz
S.
(
2013
)
The role of proteolytic processing and the stable signal peptide in expression of the Old World arenavirus envelope glycoprotein ectodomain
.
Virology
436
,
127
133
[PubMed]
107.
Bederka
L.H.
,
Bonhomme
C.J.
,
Ling
E.L.
and
Buchmeier
M.J.
(
2014
)
Arenavirus stable signal peptide is the keystone subunit for glycoprotein complex organization
.
mBio
5
,
e02063
[PubMed]
108.
Young
P.R.
and
Howard
C.R.
(
1983
)
Fine structure analysis of Pichinde virus nucleocapsids
.
J. Gen. Virol.
64
,
833
842
[PubMed]
109.
Burns
J.W.
and
Buchmeier
M.J.
(
1991
)
Protein-protein interactions in lymphocytic choriomeningitis virus
.
Virology
183
,
620
629
[PubMed]
110.
Cao
W.
,
Henry
M.D.
,
Borrow
P.
,
Yamada
H.
,
Elder
J.H.
,
Ravkov
E.V.
et al.
(
1998
)
Identification of α-Dystroglycan as a receptor for lymphocytic choriomeningitis virus and Lassa fever virus
.
Science
282
,
2079
2081
[PubMed]
111.
Kunz
S.
,
Rojek
J.M.
,
Perez
M.
,
Spiropoulou
C.F.
and
Oldstone
M.B.
(
2005
)
Characterization of the interaction of lassa fever virus with its cellular receptor alpha-dystroglycan
.
J. Virol.
79
,
5979
5987
[PubMed]
112.
Barresi
R.
and
Campbell
K.P.
(
2006
)
Dystroglycan: from biosynthesis to pathogenesis of human disease
.
J. Cell Sci.
119
,
199
207
[PubMed]
113.
Covaceuszach
S.
,
Bozzi
M.
,
Bigotti
M.G.
,
Sciandra
F.
,
Konarev
P.V.
,
Brancaccio
A.
et al.
(
2017
)
Structural flexibility of human α-dystroglycan
.
FEBS Open Bio.
7
,
1064
1077
[PubMed]
114.
Ibraghimov-Beskrovnaya
O.
,
Ervasti
J.M.
,
Leveille
C.J.
,
Slaughter
C.A.
,
Sernett
S.W.
and
Campbell
K.P.
(
1992
)
Primary structure of dystrophin-associated glycoproteins linking dystrophin to the extracellular matrix
.
Nature
355
,
696
702
[PubMed]
115.
Dempsey
C.E.
,
Bigotti
M.G.
,
Adams
J.C.
and
Brancaccio
A.
(
2019
)
Analysis of α-Dystroglycan/LG domain binding modes: investigating protein motifs that regulate the affinity of isolated LG domains
.
Front. Mol. Biosci.
6
,
18
[PubMed]
116.
Michele
D.E.
and
Campbell
K.P.
(
2003
)
Dystrophin-glycoprotein complex: post-translational processing and dystroglycan function
.
J. Biol. Chem.
278
,
15457
15460
[PubMed]
117.
Kanagawa
M.
,
Saito
F.
,
Kunz
S.
,
Yoshida-Moriguchi
T.
,
Barresi
R.
,
Kobayashi
Y.M.
et al.
(
2004
)
Molecular recognition by LARGE is essential for expression of functional dystroglycan
.
Cell
117
,
953
964
[PubMed]
118.
Jae
L.T.
,
Raaben
M.
,
Riemersma
M.
,
van Beusekom
E.
,
Blomen
V.A.
,
Velds
A.
et al.
(
2013
)
Deciphering the glycosylome of dystroglycanopathies using haploid screens for lassa virus entry
.
Science
340
,
479
483
[PubMed]
119.
Kunz
S.
,
Rojek
J.M.
,
Kanagawa
M.
,
Spiropoulou
C.F.
,
Barresi
R.
,
Campbell
K.P.
et al.
(
2005
)
Posttranslational modification of alpha-dystroglycan, the cellular receptor for arenaviruses, by the glycosyltransferase LARGE is critical for virus binding
.
J. Virol.
79
,
14282
14296
[PubMed]
120.
Yoshida-Moriguchi
T.
,
Yu
L.
,
Stalnaker
S.H.
,
Davis
S.
,
Kunz
S.
,
Madson
M.
et al.
(
2010
)
O-mannosyl phosphorylation of alpha-dystroglycan is required for laminin binding
.
Science
327
,
88
92
[PubMed]
121.
Imperiali
M.
,
Thoma
C.
,
Pavoni
E.
,
Brancaccio
A.
,
Callewaert
N.
and
Oxenius
A.
(
2005
)
O Mannosylation of alpha-dystroglycan is essential for lymphocytic choriomeningitis virus receptor function
.
J. Virol.
79
,
14297
14308
[PubMed]
122.
Rojek
J.M.
,
Spiropoulou
C.F.
,
Campbell
K.P.
and
Kunz
S.
(
2007
)
Old World and clade C New World arenaviruses mimic the molecular mechanism of receptor recognition used by alpha-dystroglycan’s host-derived ligands
.
J. Virol.
81
,
5685
5695
[PubMed]
123.
Inamori
K.
,
Yoshida-Moriguchi
T.
,
Hara
Y.
,
Anderson
M.E.
,
Yu
L.
and
Campbell
K.P.
(
2012
)
Dystroglycan function requires xylosyl- and glucuronyltransferase activities of LARGE
.
Science
335
,
93
96
[PubMed]
124.
Kunz
S.
,
Sevilla
N.
,
McGavern
D.B.
,
Campbell
K.P.
and
Oldstone
M.B.
(
2001
)
Molecular analysis of the interaction of LCMV with its cellular receptor [alpha]-dystroglycan
.
J. Cell Biol.
155
,
301
310
[PubMed]
125.
Herrador
A.
,
Fedeli
C.
,
Radulovic
E.
,
Campbell
K.P.
,
Moreno
H.
,
Gerold
G.
et al.
(
2019
)
Dynamic dystroglycan complexes mediate cell entry of Lassa virus
.
mBio
10
,
e02869
18
[PubMed]
126.
Fedeli
C.
,
Torriani
G.
,
Galan-Navarro
C.
,
Moraz
M.L.
,
Moreno
H.
,
Gerold
G.
et al.
(
2018
)
Axl can serve as entry factor for Lassa virus depending on the functional glycosylation of dystroglycan
.
J. Virol.
92
(5), e01613-17
[PubMed]
127.
Shimojima
M.
,
Ströher
U.
,
Ebihara
H.
,
Feldmann
H.
and
Kawaoka
Y.
(
2012
)
Identification of cell surface molecules involved in dystroglycan-independent Lassa virus cell entry
.
J. Virol.
86
,
2067
2078
[PubMed]
128.
Goncalves
A.R.
,
Moraz
M.L.
,
Pasquato
A.
,
Helenius
A.
,
Lozach
P.Y.
and
Kunz
S.
(
2013
)
Role of DC-SIGN in Lassa virus entry into human dendritic cells
.
J. Virol.
87
,
11504
11515
[PubMed]
129.
Brouillette
R.B.
,
Phillips
E.K.
,
Patel
R.
,
Mahauad-Fernandez
W.
,
Moller-Tank
S.
,
Rogers
K.J.
et al.
(
2018
)
TIM-1 mediates dystroglycan-independent entry of Lassa virus
.
J. Virol.
92
,
[PubMed]
130.
Shimojima
M.
and
Kawaoka
Y.
(
2012
)
Cell surface molecules involved in infection mediated by lymphocytic choriomeningitis virus glycoprotein
.
J. Vet. Med. Sci.
74
,
1363
1366
[PubMed]
131.
Shimojima
M.
,
Takada
A.
,
Ebihara
H.
,
Neumann
G.
,
Fujioka
K.
,
Irimura
T.
et al.
(
2006
)
Tyro3 family-mediated cell entry of Ebola and Marburg viruses
.
J. Virol.
80
,
10109
10116
[PubMed]
132.
Meertens
L.
,
Carnec
X.
,
Lecoin
M.P.
,
Ramdasi
R.
,
Guivel-Benhassine
F.
,
Lew
E.
et al.
(
2012
)
The TIM and TAM families of phosphatidylserine receptors mediate dengue virus entry
.
Cell Host Microbe
12
,
544
557
[PubMed]
133.
Jemielity
S.
,
Wang
J.J.
,
Chan
Y.K.
,
Ahmed
A.A.
,
Li
W.
,
Monahan
S.
et al.
(
2013
)
TIM-family proteins promote infection of multiple enveloped viruses through virion-associated phosphatidylserine
.
PLoS Pathog.
9
,
e1003232
[PubMed]
134.
Meertens
L.
,
Labeau
A.
,
Dejarnac
O.
,
Cipriani
S.
,
Sinigaglia
L.
,
Bonnet-Madin
L.
et al.
(
2017
)
Axl mediates ZIKA virus entry in human glial cells and modulates innate immune responses
.
Cell Rep.
18
,
324
333
[PubMed]
135.
Alvarez
C.P.
,
Lasala
F.
,
Carrillo
J.
,
Muñiz
O.
,
Corbí
A.L.
and
Delgado
R.
(
2002
)
C-type lectins DC-SIGN and L-SIGN mediate cellular entry by Ebola virus in cis and in trans
.
J. Virol.
76
,
6841
6844
[PubMed]
136.
Powlesland
A.S.
,
Fisch
T.
,
Taylor
M.E.
,
Smith
D.F.
,
Tissot
B.
,
Dell
A.
et al.
(
2008
)
A novel mechanism for LSECtin binding to Ebola virus surface glycoprotein through truncated glycans
.
J. Biol. Chem.
283
,
593
602
[PubMed]
137.
Martinez
M.G.
,
Bialecki
M.A.
,
Belouzard
S.
,
Cordo
S.M.
,
Candurra
N.A.
and
Whittaker
G.R.
(
2013
)
Utilization of human DC-SIGN and L-SIGN for entry and infection of host cells by the New World arenavirus, Junín virus
.
Biochem. Biophys. Res. Commun.
441
,
612
617
[PubMed]
138.
Gramberg
T.
,
Hofmann
H.
,
Möller
P.
,
Lalor
P.F.
,
Marzi
A.
,
Geier
M.
et al.
(
2005
)
LSECtin interacts with filovirus glycoproteins and the spike protein of SARS coronavirus
.
Virology
340
,
224
236
[PubMed]
139.
Acciani
M.
,
Alston
J.T.
,
Zhao
G.
,
Reynolds
H.
,
Ali
A.M.
,
Xu
B.
et al.
(
2017
)
Mutational analysis of Lassa virus glycoprotein highlights regions required for alpha-dystroglycan utilization
.
J. Virol.
91
,
e00574
17
[PubMed]
140.
Shrivastava-Ranjan
P.
,
Bergeron
É.
,
Chakrabarti
A.K.
,
Albariño
C.G.
,
Flint
M.
,
Nichol
S.T.
et al.
(
2016
)
25-hydroxycholesterol inhibition of Lassa virus infection through aberrant GP1 glycosylation
.
mBio
7
,
1
9
141.
Sevilla
N.
,
Kunz
S.
,
Holz
A.
,
Lewicki
H.
,
Homann
D.
,
Yamada
H.
et al.
(
2000
)
Immunosuppression and resultant viral persistence by specific viral targeting of dendritic cells
.
J. Exp. Med.
192
,
1249
1260
[PubMed]
142.
Sullivan
B.M.
,
Emonet
S.F.
,
Welch
M.J.
,
Lee
A.M.
,
Campbell
K.P.
,
de la Torre
J.C.
et al.
(
2011
)
Point mutation in the glycoprotein of lymphocytic choriomeningitis virus is necessary for receptor binding, dendritic cell infection, and long-term persistence
.
Proc. Natl. Acad. Sci. U.S.A.
108
,
2969
2974
[PubMed]
143.
Smelt
S.C.
,
Borrow
P.
,
Kunz
S.
,
Cao
W.
,
Tishon
A.
,
Lewicki
H.
et al.
(
2001
)
Differences in affinity of binding of lymphocytic choriomeningitis virus strains to the cellular receptor alpha-dystroglycan correlate with viral tropism and disease kinetics
.
J. Virol.
75
,
448
457
[PubMed]
144.
Vela
E.M.
,
Zhang
L.
,
Colpitts
T.M.
,
Davey
R.A.
and
Aronson
J.F.
(
2007
)
Arenavirus entry occurs through a cholesterol-dependent, non-caveolar, clathrin-mediated endocytic mechanism
.
Virology
369
,
1
11
[PubMed]
145.
Quirin
K.
,
Eschli
B.
,
Scheu
I.
,
Poort
L.
,
Kartenbeck
J.
and
Helenius
A.
(
2008
)
Lymphocytic choriomeningitis virus uses a novel endocytic pathway for infectious entry via late endosomes
.
Virology
378
,
21
33
[PubMed]
146.
Oppliger
J.
,
Torriani
G.
,
Herrador
A.
and
Kunz
S.
(
2016
)
Lassa virus cell entry via dystroglycan involves an unusual pathway of macropinocytosis
.
J. Virol.
90
,
6412
6429
[PubMed]
147.
Panda
D.
,
Das
A.
,
Dinh
P.X.
,
Subramaniam
S.
,
Nayak
D.
,
Barrows
N.J.
et al.
(
2011
)
RNAi screening reveals requirement for host cell secretory pathway in infection by diverse families of negative-strand RNA viruses
.
Proc. Natl. Acad. Sci. U.S.A.
108
,
19036
19041
[PubMed]
148.
Kerr
M.C.
and
Teasdale
R.D.
(
2009
)
Defining macropinocytosis
.
Traffic
10
,
364
371
[PubMed]
149.
Iwasaki
M.
,
Ngo
N.
and
de la Torre
J.C.
(
2014
)
Sodium hydrogen exchangers contribute to arenavirus cell entry
.
J. Virol.
88
,
643
654
[PubMed]
150.
Lin
X.P.
,
Mintern
J.D.
and
Gleeson
P.A.
(
2020
)
Macropinocytosis in different cell types: similarities and differences
.
Membranes (Basel)
10
,
177
[PubMed]
151.
Mercer
J.
and
Helenius
A.
(
2009
)
Virus entry by macropinocytosis
.
Nat. Cell Biol.
11
,
510
520
[PubMed]
152.
Nanbo
A.
,
Imai
M.
,
Watanabe
S.
,
Noda
T.
,
Takahashi
K.
,
Neumann
G.
et al.
(
2010
)
Ebolavirus is internalized into host cells via macropinocytosis in a viral glycoprotein-dependent manner
.
PLoS Pathog.
6
,
e1001121
[PubMed]
153.
Krzyzaniak
M.A.
,
Zumstein
M.T.
,
Gerez
J.A.
,
Picotti
P.
and
Helenius
A.
(
2013
)
Host cell entry of respiratory syncytial virus involves macropinocytosis followed by proteolytic activation of the F protein
.
PLoS Pathog.
9
,
e1003309
[PubMed]
154.
Hetzenecker
S.
,
Helenius
A.
and
Krzyzaniak
M.A.
(
2016
)
HCMV induces macropinocytosis for host cell entry in fibroblasts
.
Traffic
17
,
351
368
[PubMed]
155.
de Vries
E.
,
Tscherne
D.M.
,
Wienholts
M.J.
,
Cobos-Jiménez
V.
,
Scholte
F.
,
García-Sastre
A.
et al.
(
2011
)
Dissection of the influenza A virus endocytic routes reveals macropinocytosis as an alternative entry pathway
.
PLoS Pathog.
7
,
e1001329
[PubMed]
156.
Mercer
J.
and
Helenius
A.
(
2008
)
Vaccinia virus uses macropinocytosis and apoptotic mimicry to enter host cells
.
Science
320
,
531
535
[PubMed]
157.
Klewitz
C.
,
Klenk
H.D.
and
Ter Meulen
J.
(
2007
)
Amino acids from both N-terminal hydrophobic regions of the Lassa virus envelope glycoprotein GP-2 are critical for pH-dependent membrane fusion and infectivity
.
J. Gen. Virol.
88
,
2320
2328
[PubMed]
158.
Cosset
F.L.
,
Marianneau
P.
,
Verney
G.
,
Gallais
F.
,
Tordo
N.
,
Pécheur
E.I.
et al.
(
2009
)
Characterization of Lassa virus cell entry and neutralization with Lassa virus pseudoparticles
.
J. Virol.
83
,
3228
3237
[PubMed]
159.
Bulow
U.
,
Govindan
R.
and
Munro
J.B.
(
2020
)
Acidic pH triggers lipid mixing mediated by Lassa virus GP
.
Viruses
12
,
[PubMed]
160.
Israeli
H.
,
Cohen-Dvashi
H.
,
Shulman
A.
,
Shimon
A.
and
Diskin
R.
(
2017
)
Mapping of the Lassa virus LAMP1 binding site reveals unique determinants not shared by other old world arenaviruses
.
PLoS Pathog.
13
,
e1006337
[PubMed]
161.
Hulseberg
C.E.
,
Fénéant
L.
,
Szymańska
K.M.
and
White
J.M.
(
2018
)
Lamp1 increases the efficiency of Lassa virus infection by promoting fusion in less acidic endosomal compartments
.
Am. Soc. Microbiol.
9
,
e01818
17
[PubMed]
162.
Rohrer
J.
,
Schweizer
A.
,
Russell
D.
and
Kornfeld
S.
(
1996
)
The targeting of Lamp1 to lysosomes is dependent on the spacing of its cytoplasmic tail tyrosine sorting motif relative to the membrane
.
J. Cell Biol.
132
,
565
576
[PubMed]
163.
Cohen-Dvashi
H.
,
Cohen
N.
,
Israeli
H.
and
Diskin
R.
(
2015
)
Molecular mechanism for LAMP1 recognition by Lassa virus
.
J. Virol.
89
,
7584
7592
[PubMed]
164.
Cohen-Dvashi
H.
,
Israeli
H.
,
Shani
O.
,
Katz
A.
and
Diskin
R.
(
2016
)
Role of LAMP1 binding and pH sensing by the spike complex of Lassa virus
.
J. Virol.
90
,
10329
10338
[PubMed]
165.
Li
S.
,
Sun
Z.
,
Pryce
R.
,
Parsy
M.L.
,
Fehling
S.K.
,
Schlie
K.
et al.
(
2016
)
Acidic pH-induced conformations and LAMP1 binding of the Lassa virus glycoprotein spike
.
PLoS Pathog.
12
,
e1005418
[PubMed]
166.
Torriani
G.
,
Galan-Navarro
C.
and
Kunz
S.
(
2017
)
Lassa virus cell entry reveals new aspects of virus-host cell interaction
.
J. Virol.
91
,
e01902
16
[PubMed]
167.
Cohen-Dvashi
H.
,
Cohen
N.
,
Israeli
H.
and
Diskin
R.
(
2015
)
Molecular mechanism for LAMP1 recognition by lassa virus
.
J. Virol.
89
,
7584
7592
[PubMed]
168.
Guo
J.
,
Jia
X.
,
Liu
Y.
,
Cao
J.
,
Xiao
G.
and
Wang
W.
(
2021
)
Identification of residues in Lassa virus glycoprotein 1 involved in receptor switch
.
bioRxiv
169.
Zhang
X.
,
Wang
C.
,
Chen
B.
,
Wang
Q.
,
Xu
W.
,
Ye
S.
et al.
(
2019
)
Crystal structure of refolding fusion core of Lassa virus GP2 and design of Lassa virus fusion inhibitors
.
Front. Microbiol.
10
,
1829
1841
[PubMed]
170.
Shulman
A.
,
Katz
M.
,
Cohen-Dvashi
H.
,
Greenblatt
H.M.
,
Levy
Y.
and
Diskin
R.
(
2019
)
Variations in core packing of GP2 from old world mammarenaviruses in their post-fusion conformations affect membrane-fusion efficiencies
.
J. Mol. Biol.
431
,
2095
2111
[PubMed]
171.
Hastie
K.M.
,
Igonet
S.
,
Sullivan
B.M.
,
Legrand
P.
,
Zandonatti
M.A.
,
Robinson
J.E.
et al.
(
2016
)
Crystal structure of the prefusion surface glycoprotein of the prototypic arenavirus LCMV
.
Nat. Struct. Mol. Biol.
23
,
513
521
[PubMed]
172.
Gregory
S.M.
,
Harada
E.
,
Liang
B.
,
Delos
S.E.
,
White
J.M.
and
Tamm
L.K.
(
2011
)
Structure and function of the complete internal fusion loop from Ebolavirus glycoprotein 2
.
Proc. Natl. Acad. Sci. U.S.A.
108
,
11211
11216
173.
Glushakova
S.E.
,
Lukashevich
I.S.
and
Baratova
L.A.
(
1990
)
Prediction of arenavirus fusion peptides on the basis of computer analysis of envelope protein sequences
.
FEBS Lett.
269
,
145
147
[PubMed]
174.
Glushakova
S.E.
,
Omelyanenko
V.G.
,
Lukashevitch
I.S.
,
Bogdanov
A.A.
Jr
,
Moshnikova
A.B.
,
Kozytch
A.T.
et al.
(
1992
)
The fusion of artificial lipid membranes induced by the synthetic arenavirus ‘fusion peptide’
.
Biochim. Biophys. Acta
1110
,
202
208
[PubMed]
175.
Gallaher
W.R.
,
DiSimone
C.
and
Buchmeier
M.J.
(
2001
)
The viral transmembrane superfamily: possible divergence of Arenavirus and Filovirus glycoproteins from a common RNA virus ancestor
.
BMC Microbiol.
1
,
1
6
[PubMed]
176.
Durell
S.R.
,
Martin
I.
,
Ruysschaert
J.M.
,
Shai
Y.
and
Blumenthal
R.
(
1997
)
What studies of fusion peptides tell us about viral envelope glycoprotein-mediated membrane fusion (review)
.
Mol. Membr. Biol.
14
,
97
112
[PubMed]
177.
Robinson
J.E.
,
Hastie
K.M.
,
Cross
R.W.
,
Yenni
R.E.
,
Elliott
D.H.
,
Rouelle
J.A.
et al.
(
2016
)
Most neutralizing human monoclonal antibodies target novel epitopes requiring both Lassa virus glycoprotein subunits
.
Nat. Commun.
7
,
11544
[PubMed]
178.
York
J.
,
Agnihothram
S.S.
,
Romanowski
V.
and
Nunberg
J.H.
(
2005
)
Genetic analysis of heptad-repeat regions in the G2 fusion subunit of the Junín arenavirus envelope glycoprotein
.
Virology
343
,
267
274
[PubMed]
179.
Lumb
K.J.
and
Kim
P.S.
(
1995
)
A buried polar interaction imparts structural uniqueness in a designed heterodimeric coiled coil
.
Biochemistry
34
,
8642
8648
[PubMed]
180.
Cao
J.
,
Zhang
G.
,
Zhou
M.
,
Liu
Y.
,
Xiao
G.
and
Wang
W.
(
2021
)
Characterizing the Lassa virus envelope glycoprotein membrane proximal external region for its role in fusogenicity
.
Virol Sin.
36
,
273
280
[PubMed]
181.
Lee
J.
,
Nyenhuis
D.A.
,
Nelson
E.A.
,
Cafiso
D.S.
,
White
J.M.
and
Tamm
L.K.
(
2017
)
Structure of the Ebola virus envelope protein MPER/TM domain and its interaction with the fusion loop explains their fusion activity
.
Proc. Natl. Acad. Sci. U.S.A.
114
,
7987
7996
[PubMed]
182.
Salzwedel
K.
,
West
J.T.
and
Hunter
E.
(
1999
)
A conserved tryptophan-rich motif in the membrane-proximal region of the human immunodeficiency virus type 1 gp41 ectodomain is important for Env-mediated fusion and virus infectivity
.
J. Virol.
73
,
2469
2480
[PubMed]
183.
Shang
L.
,
Yue
L.
and
Hunter
E.
(
2008
)
Role of the membrane-spanning domain of human immunodeficiency virus type 1 envelope glycoprotein in cell-cell fusion and virus infection
.
J. Virol.
82
,
5417
5428
[PubMed]
184.
Vishwanathan
S.A.
and
Hunter
E.
(
2008
)
Importance of the membrane-perturbing properties of the membrane-proximal external region of human immunodeficiency virus type 1 gp41 to viral fusion
.
J. Virol.
82
,
5118
5126
[PubMed]
185.
Muñoz-Barroso
I.
,
Salzwedel
K.
,
Hunter
E.
and
Blumenthal
R.
(
1999
)
Role of the membrane-proximal domain in the initial stages of human immunodeficiency virus type 1 envelope glycoprotein-mediated membrane fusion
.
J. Virol.
73
,
6089
6092
[PubMed]
186.
Suárez
T.
,
Gallaher
W.R.
,
Agirre
A.
,
Goñi
F.M.
and
Nieva
J.L.
(
2000
)
Membrane interface-interacting sequences within the ectodomain of the human immunodeficiency virus type 1 envelope glycoprotein: putative role during viral fusion
.
J. Virol.
74
,
8038
8047
[PubMed]
187.
Zhang
L.
,
Irimia
A.
,
He
L.
,
Landais
E.
,
Rantalainen
K.
,
Leaman
D.P.
et al.
(
2019
)
An MPER antibody neutralizes HIV-1 using germline features shared among donors
.
Nat. Commun.
10
,
5389
[PubMed]
188.
Wang
Y.
,
Kaur
P.
,
Sun
Z.J.
,
Elbahnasawy
M.A.
,
Hayati
Z.
,
Qiao
Z.S.
et al.
(
2019
)
Topological analysis of the gp41 MPER on lipid bilayers relevant to the metastable HIV-1 envelope prefusion state
.
Proc. Natl. Acad. Sci. U.S.A.
116
,
22556
22566
[PubMed]
189.
Rantalainen
K.
,
Berndsen
Z.T.
,
Antanasijevic
A.
,
Schiffner
T.
,
Zhang
X.
,
Lee
W.H.
et al.
(
2020
)
HIV-1 envelope and MPER antibody structures in lipid assemblies
.
Cell Rep.
31
,
107583
[PubMed]
190.
Pinto
D.
,
Fenwick
C.
,
Caillat
C.
,
Silacci
C.
,
Guseva
S.
,
Dehez
F.
et al.
(
2019
)
Structural basis for broad HIV-1 neutralization by the MPER-specific human broadly neutralizing antibody LN01
.
Cell Host Microbe
26
,
623.e8
637.e8
[PubMed]
191.
Caillat
C.
,
Guilligay
D.
,
Sulbaran
G.
and
Weissenhorn
W.
(
2020
)
Neutralizing antibodies targeting HIV-1 gp41
.
Viruses
12
,
1210
[PubMed]
192.
de la Arada
I.
,
Torralba
J.
,
Tascón
I.
,
Colom
A.
,
Ubarretxena-Belandia
I.
,
Arrondo
J.L.R.
et al.
(
2021
)
Conformational plasticity underlies membrane fusion induced by an HIV sequence juxtaposed to the lipid envelope
.
Sci. Rep.
11
,
1278
[PubMed]
193.
Lee
J.
,
Kreutzberger
A.J.B.
,
Odongo
L.
,
Nelson
E.A.
,
Nyenhuis
D.A.
,
Kiessling
V.
et al.
(
2021
)
Ebola virus glycoprotein interacts with cholesterol to enhance membrane fusion and cell entry
.
Nat. Struct. Mol. Biol.
28
,
181
[PubMed]
194.
Parsy
M.L.
,
Harlos
K.
,
Huiskonen
J.T.
and
Bowden
T.A.
(
2013
)
Crystal structure of Venezuelan hemorrhagic fever virus fusion glycoprotein reveals a class 1 postfusion architecture with extensive glycosylation
.
J. Virol.
87
,
13070
13075
[PubMed]
195.
Liu
Y.
,
Guo
J.
,
Cao
J.
,
Zhang
G.
,
Jia
X.
,
Wang
P.
et al.
(
2021
)
Screening of botanical drugs against Lassa virus entry
.
J. Virol.
95
,
1
12
196.
York
J.
and
Nunberg
J.H.
(
2009
)
Intersubunit interactions modulate pH-induced activation of membrane fusion by the Junin virus envelope glycoprotein GPC
.
J. Virol.
83
,
4121
4126
[PubMed]
197.
York
J.
and
Nunberg
J.H.
(
2006
)
Role of the stable signal peptide of Junín arenavirus envelope glycoprotein in pH-dependent membrane fusion
.
J. Virol.
80
,
7775
7780
[PubMed]
198.
York
J.
and
Nunberg
J.H.
(
2018
)
Epistastic interactions within the Junín virus envelope glycoprotein complex provide an evolutionary barrier to reversion in the live-attenuated Candid#1 vaccine
.
J. Virol.
92
,
e01682
17
[PubMed]
199.
Messina
E.L.
,
York
J.
and
Nunberg
J.H.
(
2012
)
Dissection of the role of the stable signal peptide of the arenavirus envelope glycoprotein in membrane fusion
.
J. Virol.
86
,
6138
6145
[PubMed]
200.
York
J.
and
Nunberg
J.H.
(
2007
)
A novel zinc-binding domain is essential for formation of the functional Junín virus envelope glycoprotein complex
.
J. Virol.
81
,
13385
13391
[PubMed]
201.
Briknarová
K.
,
Thomas
C.J.
,
York
J.
and
Nunberg
J.H.
(
2011
)
Structure of a zinc-binding domain in the Junin virus envelope glycoprotein
.
J. Biol. Chem.
286
,
1528
1536
[PubMed]
202.
Shao
J.
,
Huang
Q.
,
Liu
X.
,
Di
D.
,
Dileepan
M.
,
Brisse
M.
et al.
(
2019
)
Biological characterization of conserved residues within the cytoplasmic tail of the pichinde arenaviral glycoprotein subunit 2 (GP2)
.
J. Virol.
93
,
e01277
19
[PubMed]
203.
Yolitz
J.
,
Schwing
C.
,
Chang
J.
,
Van Ryk
D.
,
Nawaz
F.
,
Wei
D.
et al.
(
2018
)
Signal peptide of HIV envelope protein impacts glycosylation and antigenicity of gp120
.
Proc. Natl. Acad. Sci. U.S.A.
115
,
2443
2448
[PubMed]
204.
Land
A.
and
Braakman
I.
(
2001
)
Folding of the human immunodeficiency virus type 1 envelope glycoprotein in the endoplasmic reticulum
.
Biochimie
83
,
783
790
[PubMed]
205.
McCaul
N.
,
Quandte
M.
,
Bontjer
I.
,
van Zadelhoff
G.
,
Land
A.
,
Crooks
E.T.
et al.
(
2021
)
Intramolecular quality control: HIV-1 envelope gp160 signal-peptide cleavage as a functional folding checkpoint
.
Cell Rep.
36
,
109646
[PubMed]
206.
Christley
S.
,
Lobo
N.F.
and
Madey
G.
(
2008
)
Multiple organism algorithm for finding ultraconserved elements
.
BMC Bioinformatics
9
,
15
[PubMed]
207.
D’Ippolito
R.A.
,
Drew
M.R.
,
Mehalko
J.
,
Snead
K.
,
Wall
V.
,
Putman
Z.
et al.
(
2021
)
Refining the N-termini of the SARS-CoV-2 spike protein and its discrete receptor-binding domain
.
J. Proteome Res.
20
,
4427
4434
[PubMed]
208.
von Heijne
G.
(
1985
)
Signal sequences. The limits of variation
.
J. Mol. Biol.
184
,
99
105
[PubMed]
209.
Zheng
N.
and
Gierasch
L.M.
(
1996
)
Signal sequences: the same yet different
.
Cell
86
,
849
852
[PubMed]
210.
Eichler
R.
,
Lenz
O.
,
Strecker
T.
,
Eickmann
M.
,
Klenk
H.D.
and
Garten
W.
(
2004
)
Lassa virus glycoprotein signal peptide displays a novel topology with an extended endoplasmic reticulum luminal region
.
J. Biol. Chem.
279
,
12293
12299
[PubMed]
211.
Schrempf
S.
,
Froeschke
M.
,
Giroglou
T.
,
von Laer
D.
and
Dobberstein
B.
(
2007
)
Signal peptide requirements for lymphocytic choriomeningitis virus glycoprotein C maturation and virus infectivity
.
J. Virol.
81
,
12515
12524
[PubMed]
212.
Agnihothram
S.S.
,
York
J.
,
Trahey
M.
and
Nunberg
J.H.
(
2007
)
Bitopic membrane topology of the stable signal peptide in the tripartite Junín virus GP-C envelope glycoprotein complex
.
J. Virol.
81
,
4331
4337
[PubMed]
213.
Froeschke
M.
,
Basler
M.
,
Groettrup
M.
and
Dobberstein
B.
(
2003
)
Long-lived signal peptide of lymphocytic choriomeningitis virus glycoprotein pGP-C
.
J. Biol. Chem.
278
,
41914
41920
[PubMed]
214.
Eichler
R.
,
Strecker
T.
,
Kolesnikova
L.
,
ter Meulen
J.
,
Weissenhorn
W.
,
Becker
S.
et al.
(
2004
)
Characterization of the Lassa virus matrix protein Z: electron microscopic study of virus-like particles and interaction with the nucleoprotein (NP)
.
Virus Res.
100
,
249
255
[PubMed]
215.
Bederka
L.H.
,
Bonhomme
C.J.
,
Ling
E.L.
and
Buchmeier
M.J.
(
2014
)
Arenavirus stable signal peptide is the keystone subunit for glycoprotein complex organization
.
mBio
5
,
1
14
216.
Strecker
T.
,
Maisa
A.
,
Daffis
S.
,
Eichler
R.
,
Lenz
O.
and
Garten
W.
(
2006
)
The role of myristoylation in the membrane association of the Lassa virus matrix protein Z
.
Virol J.
3
,
93
[PubMed]
217.
Boutin
J.A.
(
1997
)
Myristoylation
.
Cell. Signal.
9
,
15
35
[PubMed]
218.
Maurer-Stroh
S.
and
Eisenhaber
F.
(
2004
)
Myristoylation of viral and bacterial proteins
.
Trends Microbiol.
12
,
178
185
[PubMed]
219.
Harper
D.R.
and
Gilbert
R.L.
(
1995
)
Viral lipoproteins: the role of myristoylation
.
Biochem. Soc. Trans.
23
,
553
557
[PubMed]
220.
Resh
M.D.
(
1999
)
Fatty acylation of proteins: new insights into membrane targeting of myristoylated and palmitoylated proteins
.
Biochim. Biophys. Acta
1451
,
1
16
[PubMed]
221.
Göttlinger
H.G.
,
Sodroski
J.G.
and
Haseltine
W.A.
(
1989
)
Role of capsid precursor processing and myristoylation in morphogenesis and infectivity of human immunodeficiency virus type 1
.
Proc. Natl. Acad. Sci. U.S.A.
86
,
5781
5785
[PubMed]
222.
Harper
D.R.
,
Gilbert
R.L.
,
Blunt
C.
and
McIlhinney
R.A.
(
1993
)
Inhibition of varicella-zoster virus replication by an inhibitor of protein myristoylation
.
J. Gen. Virol.
74
,
1181
1184
[PubMed]
223.
Moscufo
N.
,
Simons
J.
and
Chow
M.
(
1991
)
Myristoylation is important at multiple stages in poliovirus assembly
.
J. Virol.
65
,
2372
2380
[PubMed]
224.
Marc
D.
,
Girard
M.
and
van der Werf
S.
(
1991
)
A Gly1 to Ala substitution in poliovirus capsid protein VP0 blocks its myristoylation and prevents viral assembly
.
J. Gen. Virol.
72
,
1151
1157
[PubMed]
225.
Pal
R.
,
Reitz
M.S.
Jr
,
Tschachler
E.
,
Gallo
R.C.
,
Sarngadharan
M.G.
and
Veronese
F.D.
(
1990
)
Myristoylation of gag proteins of HIV-1 plays an important role in virus assembly
.
AIDS Res. Hum. Retroviruses
6
,
721
730
[PubMed]
226.
Agnihothram
S.S.
,
Dancho
B.
,
Grant
K.W.
,
Grimes
M.L.
,
Lyles
D.S.
and
Nunberg
J.H.
(
2009
)
Assembly of arenavirus envelope glycoprotein GPC in detergent-soluble membrane microdomains
.
J. Virol.
83
,
9890
9900
[PubMed]
227.
York
J.
and
Nunberg
J.H.
(
2016
)
Myristoylation of the arenavirus envelope glycoprotein stable signal peptide is critical for membrane fusion but dispensable for virion morphogenesis
.
J. Virol.
90
,
8341
8350
[PubMed]
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