Abstract

The procollagen C-propeptides of the fibrillar collagens play key roles in the intracellular assembly of procollagen molecules from their constituent polypeptides chains, and in the extracellular assembly of collagen molecules into fibrils. Here we review recent advances in understanding the molecular mechanisms controlling C-propeptide trimerization which have revealed the importance of inter-chain disulphide bonding and a small number of charged amino acids in the stability and specificity of different types of chain association. We also show how the crystal structure of the complex between the C-propeptide trimer of procollagen III and the active fragment of procollagen C-proteinase enhancer-1 leads to a detailed model for accelerating release of the C-propeptides from procollagen by bone morphogenetic protein-1 and related proteinases. We then discuss the effects of disease-related missense mutations in the C-propeptides in relation to the sites of these mutations in the three-dimensional structure. While in general there is a good correlation between disease severity and structure-based predictions, there are notable exceptions, suggesting new interactions involving the C-propeptides yet to be characterized. Mutations affecting proteolytic release of the C-propeptides from procollagen are discussed in detail. Finally, the roles of recently discovered interaction partners for the C-propeptides are considered during fibril assembly and cross-linking.

Introduction

Collagens are the most abundant proteins in mammals (∼30% of total protein mass), where they are occur as 28 different genetic types, with each molecule consisting of three polypeptide chains containing triple-helical and globular domains [1,2]. Those that form the regular banded fibrils seen by electron microscopy are synthesized as soluble procollagen molecules with large N- and C-propeptides flanking the triple-helical domain. Procollagen synthesis is a complex process involving several intracellular compartments and accessory proteins including enzymes and chaperones [3]. The C-propeptides have long been known to (i) direct the intracellular assembly of procollagen molecule from their constituent polypeptide chains and (ii) limit further assembly into fibrils by maintaining solubility prior to proteolytic release from the rest of the molecule during secretion into the extracellular matrix (ECM). The main proteinase involved in C-propeptide release is bone morphogenetic protein-1 (BMP-1) which is assisted by another ECM protein, procollagen C-proteinase enhancer-1 (PCPE-1) that binds strongly to the C-propeptides [4]. Despite the important roles of the C-propeptides, a distinct protein module present since the dawn of the metazoa [5], only in the last few years have the underlying molecular mechanisms been revealed. Here we review these advances which not only provide answers to long-standing questions but also give insights into further roles of the C-propeptides in health and disease.

C-propeptides in intracellular assembly

During intracellular assembly of the procollagen molecule, early work showed that trimerization begins, in the rough endoplasmic reticulum (RER), by association of C-propeptides from its three polypeptide chains, followed by zipper-like folding of the triple-helical region towards the N-terminal end [6]. Depending on the procollagen type, molecules consist of three identical α1 chains (homotrimers, as in types II and III), two identical α1chains and a third non-identical α2 chain (heterotrimers, as in the usual forms of types I and V), or three non-identical chains (as in type XI). With the exception of some forms of types V and XI collagens [1], assembly of molecules from chains of different collagen types does not occur. In addition, since often the same cell synthesizes multiple collagen types, this means that ensuring the correct chain composition of each procollagen molecule requires a specific recognition mechanism between different C-propeptide domains. Clues to such a mechanism were provided by Bulleid and co-workers [7] who identified a region of 23 residues in the C-propeptide of procollagen III that when used to replace the corresponding region in a mini-procollagen chain normally incapable of homotrimerization, resulted in the formation of homotrimers. This region consists of two variable sequences, of lengths 12 and 3 residues, straddling a conserved 8 residue sequence, in the middle of an otherwise highly conserved C-propeptide sequence (∼245 residues). This discontinuous 15 residue segment, now known as the chain recognition sequence (CRS), therefore appears to play a key role in inter-chain interactions during C-propeptide trimerization.

In the absence of information on the three-dimensional structure, the molecular mechanism by which the CRS specifies inter-chain interactions remained a mystery until the first C-propeptide structure (from procollagen III) was published in 2012 (Figure 1) [8]. This revealed a previously unidentified protein-fold, with the trimer in the shape of a flower, beginning with a stalk region near the site of proteolytic release from the rest of the procollagen molecule, then a base region containing bound Ca2+ ions and inter-chain disulphide bonds and finally three petals projecting outwards from the core. When viewed down the axis from the top (Figure 1B), the long and short segments of the CRS, at each end of helix α4, interact with the short and long CRS segments, respectively, in adjacent chains. The structure therefore reveals the molecular basis of how sequence changes in the CRS can contribute to the specificity of inter-chain interactions during C-propeptide assembly.

Structure of the C-propeptide trimer of human procollagen III

Figure 1
Structure of the C-propeptide trimer of human procollagen III

(A) Structure at 3.5 Å resolution showing the stalk, base and petal regions. Each chain is shown in a different colour with Ca2+ ions in light blue. (B) Same structure rotated by 90° and viewed from the top showing the three petals, the triangle of α-helices α4 and the interaction interface (arrowheads) involving the long (wheat colour) and short (blue-green) stretches of the CRS. From [8].

Figure 1
Structure of the C-propeptide trimer of human procollagen III

(A) Structure at 3.5 Å resolution showing the stalk, base and petal regions. Each chain is shown in a different colour with Ca2+ ions in light blue. (B) Same structure rotated by 90° and viewed from the top showing the three petals, the triangle of α-helices α4 and the interaction interface (arrowheads) involving the long (wheat colour) and short (blue-green) stretches of the CRS. From [8].

A surprising observation with the C-propeptide homotrimer from procollagen III (CPIII) was that even though the amino acid sequences of all three chains are identical, close examination shows small structural differences at one of the three inter-chain interfaces, thus making the overall structure asymmetric [8]. Heterotrimeric C-propeptides are also asymmetric, since one of the three chains is the product of a different gene. These observations suggest the possibility that structural asymmetry in homotrimers could be a driving factor in the evolution of heterotrimers. In the case of procollagen I, while usually this is present as a heterotrimer, in embryonic tissues and in diseases (cancer [9–11], fibrosis [12], genetic disorders [13,14]) a homotrimeric form is observed. Unlike CPIII however, the recently determined structure of the C-propeptide homotrimer of procollagen I (homo-CPI) showed little sign of intrinsic asymmetry [15]. Instead, compared with CPIII, there are relatively few inter-chain interactions involving the CRS in homo-CPI (Figure 2).

Interaction interfaces in different C-propeptide trimers

Figure 2
Interaction interfaces in different C-propeptide trimers

(A) Charged residues at the inter-chain interface in the 1.7 Å structure of CPIII. Each chain is shown in a different colour, as in [8]. (B) Charged residues at the inter-chain interface in homo-CPI, coloured as in [15]. (C,D) Models of the two inter-chain interfaces in hetero-CPI involving the α2(I) chain. The α1(I) chains are coloured as in (B), with the α2(I) chain in blue-green. Disulphide bonds are shown in yellow. C denotes the C-terminus of each chain and * indicates the position of the inter-chain disulphide bond, which is absent from (D) leaving the free cysteine Cys64.

Figure 2
Interaction interfaces in different C-propeptide trimers

(A) Charged residues at the inter-chain interface in the 1.7 Å structure of CPIII. Each chain is shown in a different colour, as in [8]. (B) Charged residues at the inter-chain interface in homo-CPI, coloured as in [15]. (C,D) Models of the two inter-chain interfaces in hetero-CPI involving the α2(I) chain. The α1(I) chains are coloured as in (B), with the α2(I) chain in blue-green. Disulphide bonds are shown in yellow. C denotes the C-terminus of each chain and * indicates the position of the inter-chain disulphide bond, which is absent from (D) leaving the free cysteine Cys64.

Concerning the heterotrimeric form of CPI (hetero-CPI), while small angle X-ray scattering showed the overall shape to be similar to CPIII, all attempts to crystallize this form have so far been unsuccessful [15]. It has however been possible to model the structure of hetero-CPI and test this model by site-directed mutagenesis. This analysis revealed that there are just four specific inter-chain interactions (not including inter-chain disulphide bonds, see below), involving both the CRS and elsewhere in the structure, that are required for heterotrimer formation between the α2(I) chain of CPI (where the roman numeral indicates collagen type) and the two adjacent α1(I) chains (Figure 2). One of these interactions involves Glu143 in the α1(I) chain (CRS short) which forms a salt bridge with a lysine in the α2(I) chain (CRS long). Interestingly, there is a naturally occurring Glu143Lys mutation in the C-propeptide α1(I) chain that is associated with the brittle bone disease osteogenesis imperfecta (OI) type IV [16]. As expected from the modelling, insertion of this mutation into the α1(I) chain in the hetero-CPI expression system prevented the formation of heterotrimers, while assembly of homotrimers was unaffected [15].

Another important structural feature in C-propeptide assembly is the presence of inter-chain disulphide bonds. In the C-propeptides of procollagens II, III and the α1(I) chain of procollagen I, there are eight cysteines per chain, among which cysteines 1, 4, 5, 6, 7 and 8 are involved in intra-chain interactions and cysteines 2 and 3 in inter-chain interactions (indicated by * in Figure 2). Cys2 however is replaced by serine in the α2 chain of procollagen I, resulting in the absence of a disulphide bond at the corresponding inter-chain interface in the heterotrimer (Figure 2D), albeit that Cys3 in the α2 chain forms a disulphide bond with another α1 chain (Figure 2C). As shown recently by Shoulders and co-workers [17], by sedimentation equilibrium analysis, the absence of Cys2 prevents the α2(I) C-propeptide chain from forming stable homotrimers. In contrast, when Cys2 is restored by site-directed mutagenesis, stable homotrimers are formed. This contradicts earlier observations [7,18] using a mini-procollagen version of the α2(I) chain with a restored Cys2 expressed in vitro, unlike the expression of the isolated C-propeptide region in HEK293 cells [17]. Possible explanations for the discrepancy include differences in concentration of Ca2+ ions, which bind close to the inter-chain disulphide bond (Figure 2) and are both necessary and sufficient for non-covalent trimer formation [17], or perturbation of C-propeptide assembly by other regions of the mini-procollagen system. It is clear however that disulphide bonding plays a key role in stabilizing heterotrimer assembly, as demonstrated most strikingly by the finding that co-expression of α1(I) C-propeptides carrying a Cys2Ser mutation with α2(I) C-propeptides carrying a Ser2Cys mutation results in heterotrimers with a 1:2 ratio of a1(I) to a2(I) chains, unlike the normal 2:1 ratio using wild-type chains [17]. Furthermore, for all types of heterotrimers with 3 distinct chains such as the α1(V)α2(V)α3(V) form of collagen V, chain 1 contains Cys2 and Cys3, chain 2 contains only Cys3 and chain 3 contains only Cys2, as would be expected if chains 2 and 3 both form disulphide bonds with chain 1 (Figure 3). The role of the CRS and other regions containing collagen type-specific residues involved in inter-chain interactions is therefore to fine-tune the specificity of trimerization once inter-chain disulphide bonding has determined the overall stoichiometry (homotrimer 1:1:1, heterotrimer 2:1 or heterotrimer 1:2:3).

Prediction of collagen trimerization propensities based on the pattern of cysteines C2 and C3 involved in inter-chain disulphide bonds (C1 and C4 form an intra-chain S–S bond)

Figure 3
Prediction of collagen trimerization propensities based on the pattern of cysteines C2 and C3 involved in inter-chain disulphide bonds (C1 and C4 form an intra-chain S–S bond)

(A) Known disulphide-bonding network for a homotrimeric collagen strand with C2 and C3 intact. (B) Inter-chain disulphide bonds cannot form in the absence of C2 or C3. (C) Predicted disulphide-bonding networks for a collagen heterotrimer with two identical chains and a third chain lacking C2 or C3. (D) Predicted disulphide-bonding network for a collagen heterotrimer consisting of one chain with cysteines C2 and C3, one chain with C2 only and one chain with C3 only. From [17].

Figure 3
Prediction of collagen trimerization propensities based on the pattern of cysteines C2 and C3 involved in inter-chain disulphide bonds (C1 and C4 form an intra-chain S–S bond)

(A) Known disulphide-bonding network for a homotrimeric collagen strand with C2 and C3 intact. (B) Inter-chain disulphide bonds cannot form in the absence of C2 or C3. (C) Predicted disulphide-bonding networks for a collagen heterotrimer with two identical chains and a third chain lacking C2 or C3. (D) Predicted disulphide-bonding network for a collagen heterotrimer consisting of one chain with cysteines C2 and C3, one chain with C2 only and one chain with C3 only. From [17].

C-propeptides in extracellular assembly

In addition to their roles in intracellular assembly of procollagen molecules, the C-propeptides also control the assembly of collagen fibrils in the ECM. Release of the C-propeptides from the pC-collagen molecule (procollagen lacking the N-propeptides) decreases its solubility by 1000-fold, thus leading to spontaneous fibril assembly [19]. The proteinase mainly responsible for the cleavage of the C-propeptides is BMP-1 [20,21], though other BMP-1/tolloid-like proteinases (BTPs) can also fulfil this role [4] (Figure 4). Indeed, it has been shown that other members of the astacin family of metalloproteinases, meprins, are also capable of releasing the C-propeptides from procollagens [22,23]. In the case of the BTPs, but not the meprins, cleavage of the C-propeptides is accelerated (by up to 20-fold) by another ECM protein, PCPE-1 [24,25] which lacks intrinsic proteolytic activity but shares with BTPs the presence of CUB domains (Figure 4).

Domain structures of BTPs, meprins and PCPEs

Figure 4
Domain structures of BTPs, meprins and PCPEs

mTLD is an alternatively spliced product of the bmp1 gene that also encodes BMP-1. Note the presence of CUB domains in BTPs and PCPEs but not in meprins.

Figure 4
Domain structures of BTPs, meprins and PCPEs

mTLD is an alternatively spliced product of the bmp1 gene that also encodes BMP-1. Note the presence of CUB domains in BTPs and PCPEs but not in meprins.

While BTPs are known to act on approximately 30 substrates (mostly ECM proteins or growth factors and their antagonists), acceleration of their activity by PCPE-1 is limited to the procollagen propeptides [26,27]. Compared to using inhibitors of BTPs with the risk of off-target effects, there is interest in blocking PCPE-1 as a way of specifically preventing the excessive accumulation of collagen in fibrotic diseases [28–33]. A necessary prerequisite for this is to understand the molecular mechanism of action of PCPE-1, an area in which there has been considerable progress in recent years. First, it is clear that PCPE-1 acts by binding to the procollagen substrate rather than to the proteinase. More specifically, binding is to the C-propeptide region only and the contiguous CUB1CUB2 fragment of PCPE-1 is both necessary and sufficient for enhancing activity [34,35]. Secondly, binding requires acidic residues involved in Ca2+ binding in the CUB domains of PCPE-1 which form salt bridges with conserved lysines in the stalk/base region of the C-propeptide trimer [36,37]. Also, despite there being three chains, only one molecule of PCPE-1 is bound to the trimer. Third, the presence of PCPE-1 increases the affinity of BMP-1 for its procollagen substrate as well as increasing the reaction rate, as shown using both procollagen I [38] and procollagen III [37] substrates. This suggests that binding of PCPE-1 to the C-propeptide might create a higher affinity interaction surface for BMP-1 and/or lead to a conformational change (in the substrate, the enzyme, or both) that increases catalytic activity.

Recently, important new insights into the mechanism of enhancement of BMP-1 activity have been obtained with the determination of the crystal structure of the complex between the C-propeptide trimer of procollagen III (CPIII) and the CUB1CUB2 fragment of PCPE-1 (Figure 5A) [39]. This confirms that CUB1CUB2 binds to the stalk/base region of CPIII, as previously suggested by mutagenesis and small angle scattering data [37]. Furthermore, it reveals why the stoichiometry of binding is only 1:1, since CUB1 binds mainly to chain A of CPIII and CUB2 binds mainly to chain B, leaving only chain C available for further interactions. As it was previously shown that both the CUB1 and CUB2 domains must be bound for enhancing activity [34], there are not enough sites on CPIII available for additional binding. Most interestingly however, the structure shows the end of the stalk region of chain A (shown in magenta colour in Figure 5) to be ‘pulled’ into the interface between the CUB1 and CUB2 domains of PCPE-1, thus separating chain A away from the other two chains. This interaction is stabilized by interactions involving three residues in CUB1CUB2 which when mutated to alanine almost abolish enhancing activity [39]. These observations support the idea that the role of PCPE-1 is to introduce a conformational change in the substrate that facilitates cleavage by BMP-1. Using the crystal structure as a template, it was then possible to model the catalytic domain of BMP-1 [40] with the cleavage site of chain A (not seen in the crystal structure) bound to the active site as a result of being pulled into the CUB1CUB2 interface (Figure 5B). Since the active site of BMP-1 is too small to accommodate all three chains, this provides a mechanism for increasing catalytic efficiency. In addition, the model allows the BMP-1 catalytic domain to bind to the CUB1CUB2 region of PCPE-1, thus further contributing to enhancing activity.

Structures of the CPIII:CUB1CUB2 complex

Figure 5
Structures of the CPIII:CUB1CUB2 complex

(A) Side view showing the CUB1CUB2 fragment of PCPE -1 attached to the stalk/base region of CPIII. The individual chains of CPIII (A, B, C) are in magenta, orange and grey, respectively, and the CUB1 and CUB2 domains of PCPE-1 in dark green and olive green, respectively. Ca2+ ions are the cyan spheres. The linker connecting CUB1 and CUB2 (absent from the electron density map) is shown as a dotted line. (B) Molecular modelling of the N-terminal extensions of CPIII and the interactions of the BMP-1 catalytic domain. Beginning with the structure of the CPIII-His:C1C2 complex, modelling extends chains A, B and C of CPIII towards the C-telopeptide region. Chain A is first pulled into the cleft between CUB1 and CUB2 then enters the active site of the BMP-1 catalytic domain where the P1′ residue, Asp1, interacts with Arg176 in the S1′ pocket, in close proximity to the essential Glu93 and the catalytic water molecule bound to the active site zinc (light green sphere). The negative sign indicates residues on the non-prime side of the cleavage site. From [39].

Figure 5
Structures of the CPIII:CUB1CUB2 complex

(A) Side view showing the CUB1CUB2 fragment of PCPE -1 attached to the stalk/base region of CPIII. The individual chains of CPIII (A, B, C) are in magenta, orange and grey, respectively, and the CUB1 and CUB2 domains of PCPE-1 in dark green and olive green, respectively. Ca2+ ions are the cyan spheres. The linker connecting CUB1 and CUB2 (absent from the electron density map) is shown as a dotted line. (B) Molecular modelling of the N-terminal extensions of CPIII and the interactions of the BMP-1 catalytic domain. Beginning with the structure of the CPIII-His:C1C2 complex, modelling extends chains A, B and C of CPIII towards the C-telopeptide region. Chain A is first pulled into the cleft between CUB1 and CUB2 then enters the active site of the BMP-1 catalytic domain where the P1′ residue, Asp1, interacts with Arg176 in the S1′ pocket, in close proximity to the essential Glu93 and the catalytic water molecule bound to the active site zinc (light green sphere). The negative sign indicates residues on the non-prime side of the cleavage site. From [39].

Though the new structural data give important insights into cleavage of procollagen by BTPs, much remains to be learned. For example, how are the remaining chains cleaved following proteolysis of chain A? Also, what are the roles of the non-catalytic domains of BMP-1 and other BTPs? Small angle scattering indicates that these are folded back towards the catalytic domain [41]. The presence of CUB domains in BMP-1 is clearly critical for both catalytic activity and enhancement by PCPE-1, as shown by a mutation in the CUB2 domain of BMP-1 that blocks activity completely [42], and by the fact that the activities of meprins (which are devoid of CUB domains) are not enhanced by PCPE-1 [22].

C-propeptides in disease and novel functions

So far approximately 300 mutations (including missense, nonsense, frameshift and silent mutations) have been described in the C-propeptides of procollagens I, II, III and V (https://www.le.ac.uk/ge/collagen, https://databases.lovd.nl/shared/genes/COL2A1). Most of these are associated with major disorders such as OI (and other skeletal dysplasias) and Ehlers–Danlos syndrome (affecting the skin and vascular system). Among them, about a third are missense mutations whose positions have been mapped in three dimensions [43–46] using the crystal structures of the C-propeptides of procollagens I [15] and III [8]. For mutations in the α1-chain of procollagen I (COL1A1 gene), in most cases, there is a correlation between the position of the mutation and the severity of the disease. Those that interfere with disulphide bonding, hydrogen bonding, inter-chain interactions, Ca2+ binding or stability of the hydrophobic core are usually associated with severe phenotypes. In contrast, mutations located on the outer surface of the petal region, remote from inter-chain interactions, are generally mild. There are exceptions to this rule however, such as p.Asp1413(195)Asn and p.Asp1441(223)Tyr (where the first number is relative to the transcription start site and second number is from the start of the C-propeptide domain), both of which are on the outer surface of the petal but lead to severe or lethal phenotypes, respectively [46,47]. A possible explanation for this paradox is the recent discovery [46] that these mutations lead to mislocalization of procollagen I to the lumen of the RER, in contrast with the wild-type protein which is membrane bound. Such an interaction with the RER had previously been suspected of being important in collagen biosynthesis [3,48]; these latest results strongly support this hypothesis, though the mechanism of binding remains to be elucidated.

In contrast with COL1A1, for mutations in the C-propeptide of α2 chain of procollagen I (COL1A2 gene), there is a relatively poor correlation between predicted and observed phenotypes [43]. This could be due to the fact that, for heterozygous mutations, 50% of procollagen molecules will be normal, unlike for COL1A1 mutations where 75% of molecules will have one or two defective chains. Alternatively, defective α2 chains could be replaced by normal α1 chains resulting in proα1(I)3 homotrimers.

For both COLA1 and COL1A2, there has been considerable interest in recent years in missense mutations in the Ala and Asp residues that define the proteolytic cleavage site for release of the C-propeptides from procollagen I [49–53]. These mutations, which are heterozygous, give rise to a relatively mild form of OI similar to type I but distinguished by unusually dense bones. While bone mineral density in these patients is high, paradoxically there is also delayed mineralization as shown by increased amounts of unmineralized osteoid. A similar phenotype has been observed in patients for some [54,55], but not all [56,57], mutations in BMP-1, all of which are either homozygous or bi-allelic. Since both cleavage-site and BMP-1 mutations interfere with cleavage of the C-propeptides, there will be an increase in the population of partially processed procollagen molecules with intact C-propeptides on one or more chains. (Note that not all procollagen chains will be affected in these patients, either because the C-propeptide mutations are heterozygous, or because other proteinases can take over from defective BMP-1, such as mTLL-1 or meprins.) Such mutations may therefore affect the rate of collagen deposition in osteoid and other tissues, and also the regulation of collagen synthesis by C-propeptide-mediated feedback control, as observed previously for both preosteoblasts [58] and fibroblasts [59,60]. Concerning bone mineralization, collagen fibrils play a key role in this process, either by nucleating mineral deposition directly or via non-collagenous proteins [61–63]. In particular, there is a positively charged region in the fibril corresponding to the C-terminal end of the collagen molecule that appears to play a key role in calcium phosphate accumulation [64]. The increased presence of C-propeptides on the surface of collagen fibrils in patients with defective C-terminal processing may amplify this effect, leading to hypermineralization, particularly as the C-propeptides (also known as chondrocalcin in the case of procollagen II) have themselves been implicated in the mineralization process [65].

Concerning novel functions, the heterotrimeric form of CPI (unlike CPII [10]) has been reported to be chemotactic for endothelial and mammary carcinoma cells, inducing the expression of VEGF and CXCR4, suggesting a role in tumour growth and angiogenesis [66–69]. Also, in addition to previously known binding partners including PCPEs, integrins [70] and chaperone proteins [71], the C-propeptides of procollagen I have recently been found to bind to the ECM proteins thrombospondin-1 (TSP1) and lysyl oxidase [72] (Figure 6). In addition, TSP1 binds to PCPE-1 [73] and to a positively-charged KGHR sequence in the collagen molecule involved in lysyl oxidase initiated cross-linking to the C-terminal region of an adjacent molecule in the fibril [72]. Furthermore, the proteoglycan fibromodulin (FMOD) binds to the same KGHR sequence in collagen and also to lysyl oxidase [74]. In view of all these interactions occurring in the vicinity of the C-terminal end of the collagen molecule (including its C-propeptides) and the importance of this region in mineral deposition, this opens the way to further studies on the complexity of the factors controlling the assembly, cross-linking and mineralization of the collagen fibril.

Diagram of the interactions found in the region of the C-terminal end of one collagen molecule within the collagen fibril

Figure 6
Diagram of the interactions found in the region of the C-terminal end of one collagen molecule within the collagen fibril

Collagen molecules are shown as grey rectangles where the dotted lines indicate other parts in each molecule not shown in the figure. Molecule 1 (top left) has its C-terminal end on the right, while molecule 3 (bottom) is staggered such that its N-terminal end forms cross-links with molecule 1. The N-terminal end of molecule 2 (top right) is staggered relative to molecule 3 revealing the gap region between it and molecule 1. CPI: C-propeptide trimer of procollagen I; proLOX: prolysylyl oxidase.

Figure 6
Diagram of the interactions found in the region of the C-terminal end of one collagen molecule within the collagen fibril

Collagen molecules are shown as grey rectangles where the dotted lines indicate other parts in each molecule not shown in the figure. Molecule 1 (top left) has its C-terminal end on the right, while molecule 3 (bottom) is staggered such that its N-terminal end forms cross-links with molecule 1. The N-terminal end of molecule 2 (top right) is staggered relative to molecule 3 revealing the gap region between it and molecule 1. CPI: C-propeptide trimer of procollagen I; proLOX: prolysylyl oxidase.

Conclusion

Recent years have seen considerable progress in elucidating the molecular mechanisms by which the C-propeptides control intracellular procollagen trimerization and extracellular proteolytic processing. A number of areas remain for future study however, notably the 3D structures of the CPI heterotrimer and the C-propeptides of procollagen II, as well as the interactions and signalling functions of the C-propeptides, with membranes and in cross-linking and mineralization, feedback control of collagen biosynthesis, and tumour growth and angiogenesis.

Summary

  • Procollagen C-propeptides control both intra- and extracellular assembly during collagen biosynthesis.

  • Disulphide-bonding patterns and specific inter-chain interactions direct C-propeptide trimerization.

  • Binding of PCPE-1 to the C-propeptide trimer provides a mechanism for accelerated proteolytic release.

  • Mutations in C-propeptides account for debilitating diseases often with specific phenotypes.

  • Recently discovered interaction partners of the C-propeptides give new insights into their roles.

Acknowledgements

I am grateful to the many friends and colleagues who have shared with me this interest in the procollagen C-propeptides over many years.

Competing Interests

The author declares that there are no competing interests associated with the manuscript.

Abbreviations

     
  • BMP-1

    bone morphogenetic protein-1

  •  
  • BTPs

    BMP-1/tolloid-like proteinases

  •  
  • CRS

    chain recognition sequence

  •  
  • ECM

    extracellular matrix

  •  
  • FMOD

    fibromodulin

  •  
  • OI

    osteogenesis imperfecta

  •  
  • PCPE-1

    procollagen C-proteinase enhancer-1

  •  
  • RER

    rough endoplasmic reticulum

  •  
  • TSP1

    thrombospondin-1

References

References
1.
Ricard-Blum
S.
(
2011
)
The collagen family
.
Cold Spring Harb. Perspect. Biol.
3
,
a004978
[PubMed]
2.
Bella
J.
and
Hulmes
D.J.S.
(
2017
)
Fibrillar collagens
.
Subcell. Biochem.
82
,
457
490
[PubMed]
3.
Ishikawa
Y.
and
Bachinger
H.P.
(
2013
)
A molecular ensemble in the rER for procollagen maturation
.
Biochim. Biophys. Acta
1833
,
2479
2491
[PubMed]
4.
Vadon-Le Goff
S.
,
Hulmes
D.J.S.
and
Moali
C.
(
2015
)
BMP-1/tolloid-like proteinases synchronize matrix assembly with growth factor activation to promote morphogenesis and tissue remodeling
.
Matrix Biol.
44–46
,
14
23
5.
Exposito
J.Y.
,
Valcourt
U.
,
Cluzel
C.
and
Lethias
C.
(
2010
)
The fibrillar collagen family
.
Int. J. Mol. Sci.
11
,
407
426
[PubMed]
6.
Engel
J.
and
Prockop
D.J.
(
1991
)
The zipper-like folding of collagen triple helices and the effects of mutations that disrupt the zipper
.
Ann. Rev. Biophys. Biophys. Chem.
20
,
137
152
7.
Lees
J.F.
,
Tasab
M.
and
Bulleid
N.J.
(
1997
)
Identification of the molecular recognition sequence which determines the type-specific assembly of procollagen
.
EMBO J.
16
,
908
916
[PubMed]
8.
Bourhis
J.M.
,
Mariano
N.
,
Zhao
Y.
,
Harlos
K.
,
Exposito
J.Y.
,
Jones
E.Y.
et al.
(
2012
)
Structural basis of fibrillar collagen trimerization and related genetic disorders
.
Nat. Struct. Mol. Biol.
19
,
1031
1036
[PubMed]
9.
Makareeva
E.
,
Han
S.
,
Vera
J.C.
,
Sackett
D.L.
,
Holmbeck
K.
,
Phillips
C.L.
et al.
(
2010
)
Carcinomas contain a matrix metalloproteinase-resistant isoform of type I collagen exerting selective support to invasion
.
Cancer Res.
70
,
4366
4374
[PubMed]
10.
Vincourt
J.B.
,
Etienne
S.
,
Cottet
J.
,
Delaunay
C.
,
Malanda
C.B.
,
Lionneton
F.
et al.
(
2010
)
C-propeptides of procollagens I alpha 1 and II that differentially accumulate in enchondromas versus chondrosarcomas regulate tumor cell survival and migration
.
Cancer Res.
70
,
4739
4748
[PubMed]
11.
Delaunay-Lemarie
C.
,
Vincourt
J.B.
,
Marie
B.
,
Battaglia-Hsu
S.F.
,
Etienne
S.
,
Sirveaux
F.
et al.
(
2015
)
In malignant cartilagenous tumors, immunohistochemical expression of procollagen PC1CP peptide is higher and that of PC2CP lower than in benign cartilaginous lesions
.
Virchows Arch.
467
,
329
337
[PubMed]
12.
Brodeur
A.C.
,
Roberts-Pilgrim
A.M.
,
Thompson
K.L.
,
Franklin
C.L.
and
Phillips
C.L.
(
2017
)
Transforming growth factor-beta1/Smad3-independent epithelial-mesenchymal transition in type I collagen glomerulopathy
.
Int. J. Nephrol. Renovasc. Dis.
10
,
251
259
[PubMed]
13.
Pace
J.M.
,
Wiese
M.
,
Drenguis
A.S.
,
Kuznetsova
N.
,
Leikin
S.
,
Schwarze
U.
et al.
(
2008
)
Defective C-propeptides of the proalpha2(I) chain of type I procollagen impede molecular assembly and result in osteogenesis imperfecta
.
J. Biol. Chem.
283
,
16061
16067
[PubMed]
14.
Malfait
F.
,
Symoens
S.
,
Coucke
P.
,
Nunes
L.
,
De Almeida
S.
and
De Paepe
A.
(
2006
)
Total absence of the α2(I) chain of collagen type I causes a rare form of Ehlers–Danlos syndrome with hypermobility and propensity to cardiac valvular problems
.
J. Med. Genet.
43
,
e36
[PubMed]
15.
Sharma
U.
,
Carrique
L.
,
Vadon-Le Goff
S.
,
Mariano
N.
,
Georges
R.N.
,
Delolme
F.
et al.
(
2017
)
Structural basis of homo- and heterotrimerization of collagen I
.
Nat. Commun.
8
,
14671
[PubMed]
16.
Roughley
P.J.
(
2016
)
Osteogenesis Imperfecta Variant Database ID: COL1A1_00537
.
17.
DiChiara
A.S.
,
Li
R.C.
,
Suen
P.H.
,
Hosseini
A.S.
,
Taylor
R.J.
,
Weickhardt
A.F.
et al.
(
2018
)
A cysteine-based molecular code informs collagen C-propeptide assembly
.
Nat. Commun.
9
,
4206
[PubMed]
18.
Lees
J.F.
and
Bulleid
N.J.
(
1994
)
The role of cysteine residues in the folding and association of the COOH-terminal propeptide of types I and III procollagen
.
J. Biol. Chem.
269
,
24354
24360
[PubMed]
19.
Kadler
K.E.
,
Hojima
Y.
and
Prockop
D.J.
(
1987
)
Assembly of collagen fibrils de novo by cleavage of the type I pC- collagen with procollagen C-proteinase. Assay of critical concentration demonstrates that collagen self-assembly is a classical example of an entropy-driven process
.
J. Biol. Chem.
262
,
15696
15701
20.
Kessler
E.
,
Takahara
K.
,
Biniaminov
L.
,
Brusel
M.
and
Greenspan
D.S.
(
1996
)
Bone morphogenetic protein-1: the type I procollagen C-proteinase
.
Science
271
,
360
362
[PubMed]
21.
Li
S.W.
,
Sieron
A.L.
,
Fertala
A.
,
Hojima
Y.
,
Arnold
W.V.
and
Prockop
D.J.
(
1996
)
The C-proteinase that processes procollagens to fibrillar collagens is identical to the protein previously identified as bone morphogenic protein-1
.
Proc. Natl. Acad. Sci. USA
93
,
5127
5130
22.
Kronenberg
D.
,
Bruns
B.C.
,
Moali
C.
,
Vadon-Le Goff
S.
,
Sterchi
E.E.
,
Traupe
H.
et al.
(
2010
)
Processing of procollagen III by meprins: new players in extracellular matrix assembly?
J. Invest. Dermatol.
130
,
2727
2735
[PubMed]
23.
Broder
C.
,
Arnold
P.
,
Vadon-Le Goff
S.
,
Konerding
M.A.
,
Bahr
K.
,
Muller
S.
et al.
(
2013
)
Metalloproteases meprin alpha and meprin beta are C- and N-procollagen proteinases important for collagen assembly and tensile strength
.
Proc. Natl. Acad. Sci. USA
110
,
14219
14224
24.
Adar
R.
,
Kessler
E.
and
Goldberg
B.
(
1986
)
Evidence for a protein that enhances the activity of type I procollagen C-proteinase
.
Coll. Relat. Res.
6
,
267
277
25.
Takahara
K.
,
Kessler
E.
,
Biniaminov
L.
,
Brusel
M.
,
Eddy
R.L.
,
Janisait
S.
et al.
(
1994
)
Type I procollagen COOH-terminal proteinase enhancer protein: identification, primary structure, and chromosomal localization of the cognate human gene (PCOLCE)
.
J. Biol. Chem.
269
,
26280
26285
[PubMed]
26.
Moali
C.
,
Font
B.
,
Ruggiero
F.
,
Eichenberger
D.
,
Rousselle
P.
,
Francois
V.
et al.
(
2005
)
Substrate-specific modulation of a multisubstrate proteinase. C-terminal processing of fibrillar procollagens is the only BMP-1-dependent activity to be enhanced by PCPE-1
.
J. Biol. Chem.
280
,
24188
24194
[PubMed]
27.
Petropoulou
V.
,
Garrigue-Antar
L.
and
Kadler
K.E.
(
2005
)
Identification of the minimal domain structure of bone morphogenetic protein-1 (BMP-1) for chordinase activity: chordinase activity is not enhanced by procollagen C-proteinase enhancer-1 (PCPE-1)
.
J. Biol. Chem.
280
,
22616
22623
[PubMed]
28.
Beaumont
J.
,
Lopez
B.
,
Hermida
N.
,
Schroen
B.
,
San
J.G.
,
Heymans
S.
et al.
(
2014
)
microRNA-122 down-regulation may play a role in severe myocardial fibrosis in human aortic stenosis through TGF-beta1 up-regulation
.
Clin. Sci. (Lond.)
126
,
497
506
[PubMed]
29.
Ma
L.
,
Gan
C.
,
Huang
Y.
,
Wang
Y.
,
Luo
G.
and
Wu
J.
(
2014
)
Comparative proteomic analysis of extracellular matrix proteins secreted by hypertrophic scar with normal skin fibroblasts
.
Burns Trauma
2
,
76
83
[PubMed]
30.
Hassoun
E.
,
Safrin
M.
,
Ziv
H.
,
Pri-Chen
S.
and
Kessler
E.
(
2016
)
Procollagen C-proteinase enhancer 1 (PCPE-1) as a plasma marker of muscle and liver fibrosis in mice
.
PLoS One
11
,
e0159606
[PubMed]
31.
Ippolito
D.L.
,
AbdulHameed
M.D.
,
Tawa
G.J.
,
Baer
C.E.
,
Permenter
M.G.
,
McDyre
B.C.
et al.
(
2016
)
Gene expression patterns associated with histopathology in toxic liver fibrosis
.
Toxicol. Sci.
149
,
67
88
[PubMed]
32.
Hassoun
E.
,
Safrin
M.
,
Wineman
E.
,
Weiss
P.
and
Kessler
E.
(
2017
)
Data comparing the plasma levels of procollagen C-proteinase enhancer 1 (PCPE-1) in healthy individuals and liver fibrosis patients
.
Data Brief
14
,
777
781
[PubMed]
33.
Ozkan
G.
,
Guzel
S.
,
Atar
R.V.
,
Fidan
C.
,
Kara
S.P.
and
Ulusoy
S.
(
2018
)
Elevated serum levels of PCPE-1 in patients with chronic kidney disease is associated with a declining glomerular filtration rate
.
Nephrology (Carlton)
[PubMed]
34.
Kronenberg
D.
,
Vadon-Le Goff
S.
,
Bourhis
J.M.
,
Font
B.
,
Eichenberger
D.
,
Hulmes
D.J.S.
et al.
(
2009
)
Strong cooperativity and loose geometry between CUB domains are the basis for procollagen C-proteinase enhancer activity
.
J. Biol. Chem.
284
,
33437
33446
[PubMed]
35.
Vadon-Le Goff
S.
,
Kronenberg
D.
,
Bourhis
J.M.
,
Bijakowski
C.
,
Raynal
N.
,
Ruggiero
F.
et al.
(
2011
)
Procollagen C-proteinase enhancer stimulates procollagen processing by binding to the C-propeptide only
.
J. Biol. Chem.
286
,
38932
38938
[PubMed]
36.
Blanc
G.
,
Font
B.
,
Eichenberger
D.
,
Moreau
C.
,
Ricard-Blum
S.
,
Hulmes
D.J.S.
et al.
(
2007
)
Insights into how CUB domains can exert specific functions while sharing a common fold: conserved and specific features of the CUB1 domain contribute to the molecular basis of procollagen C-proteinase enhancer-1 activity
.
J. Biol. Chem.
282
,
16924
16933
[PubMed]
37.
Bourhis
J.M.
,
Vadon-Le Goff
S.
,
Afrache
H.
,
Mariano
N.
,
Kronenberg
D.
,
Thielens
N.M.
et al.
(
2013
)
Procollagen C-proteinase enhancer grasps the stalk of the C-propeptide trimer to boost collagen precursor maturation
.
Proc. Natl. Acad. Sci. USA
110
,
6394
6399
38.
Moschcovich
L.
and
Kessler
E.
(
2016
)
Data comparing the kinetics of procollagen type I processing by bone morphogenetic protein 1 (BMP-1) with and without procollagen C-proteinase enhancer 1 (PCPE-1)
.
Data Brief
9
,
883
887
[PubMed]
39.
Pulido
D.
,
Sharma
U.
,
Vadon-Le
G.S.
,
Hussain
S.A.
,
Cordes
S.
,
Mariano
N.
et al.
(
2018
)
Structural basis for the acceleration of procollagen processing by procollagen c-proteinase enhancer-1
.
Structure
26
,
1384
1392
[PubMed]
40.
MacSweeney
A.
,
Gil-Parrado
S.
,
Vinzenz
D.
,
Bernardi
A.
,
Hein
A.
,
Bodendorf
U.
et al.
(
2008
)
Structural basis for the substrate specificity of bone morphogenetic protein 1/tolloid-like metalloproteases
.
J. Mol. Biol.
384
,
228
239
[PubMed]
41.
Berry
R.
,
Jowitt
T.A.
,
Ferrand
J.
,
Roessle
M.
,
Grossmann
J.G.
,
Canty-Laird
E.G.
et al.
(
2009
)
Role of dimerization and substrate exclusion in the regulation of bone morphogenetic protein-1 and mammalian tolloid
.
Proc. Natl. Acad. Sci. USA
106
,
8561
8566
42.
Hartigan
N.
,
Garrigue-Antar
L.
and
Kadler
K.E.
(
2003
)
Bone morphogenetic protein-1 (BMP-1). Identification of the minimal domain structure for procollagen C-proteinase activity
.
J. Biol. Chem.
278
,
18045
18049
[PubMed]
43.
Symoens
S.
,
Hulmes
D.J.S.
,
Bourhis
J.M.
,
Coucke
P.J.
,
De
P.A.
and
Malfait
F.
(
2014
)
Type I procollagen C-propeptide defects: study of genotype-phenotype correlation and predictive role of crystal structure
.
Hum. Mutat.
35
,
1330
1341
[PubMed]
44.
Lu
Y.
,
Ren
X.
,
Wang
Y.
,
Li
T.
,
Li
F.
,
Wang
S.
et al.
(
2014
)
Mutational and structural characteristics of four novel heterozygous C-propeptide mutations in the proalpha1(I) collagen gene in Chinese osteogenesis imperfecta patients
.
Clin. Endocrinol. (Oxf)
80
,
524
531
[PubMed]
45.
Stembridge
N.S.
,
Vandersteen
A.M.
,
Ghali
N.
,
Sawle
P.
,
Nesbitt
M.
,
Pollitt
R.C.
et al.
(
2015
)
Clinical, structural, biochemical and X-ray crystallographic correlates of pathogenicity for variants in the C-propeptide region of the COL3A1 gene
.
Am. J. Med. Genet. A
167A
,
1763
1772
[PubMed]
46.
Barnes
A.M.
,
Ashok
A.
,
Makareeva
E.N.
,
Brusel
M.
,
Cabral
W.A.
,
Weis
M.A.
et al.
(
2019
)
COL1A1 C-propeptide mutations cause ER mislocalization of procollagen and impair C-terminal processing
.
Biochim. Biophys. Acta–Mol. Basis Dis.
,
in press
47.
Pace
J.M.
,
Chitayat
D.
,
Atkinson
M.
,
Wilcox
W.R.
,
Schwarze
U.
and
Byers
P.H.
(
2002
)
A single amino acid substitution (D1441Y) in the carboxyl-terminal propeptide of the proalpha1(I) chain of type I collagen results in a lethal variant of osteogenesis imperfecta with features of dense bone diseases
.
J. Med. Genet.
39
,
23
29
[PubMed]
48.
Beck
K.
,
Boswell
B.A.
,
Ridgway
C.C.
and
Bachinger
H.P.
(
1996
)
Triple helix formation of procollagen type I can occur at the rough endoplasmic reticulum membrane
.
J. Biol. Chem.
271
,
21566
21573
[PubMed]
49.
Lindahl
K.
,
Barnes
A.M.
,
Fratzl-Zelman
N.
,
Whyte
M.P.
,
Hefferan
T.E.
,
Makareeva
E.
et al.
(
2011
)
COL1 C-propeptide cleavage site mutations cause high bone mass osteogenesis imperfecta
.
Hum. Mutat.
32
,
598
609
[PubMed]
50.
McInerney-Leo
A.M.
,
Duncan
E.L.
,
Leo
P.J.
,
Gardiner
B.
,
Bradbury
L.A.
,
Harris
J.E.
et al.
(
2015
)
COL1A1 C-propeptide cleavage site mutation causes high bone mass, bone fragility and jaw lesions: a new cause of gnathodiaphyseal dysplasia?
Clin. Genet.
88
,
49
55
[PubMed]
51.
Nishimura
G.
,
Nakajima
M.
,
Takikawa
K.
,
Haga
N.
and
Ikegawa
S.
(
2016
)
Distinctive skeletal phenotype in high bone mass osteogenesis imperfecta due to a COL1A2 cleavage site mutation
.
Am. J. Med. Genet. A
170
,
2212
2214
[PubMed]
52.
Rolvien
T.
,
Kornak
U.
,
Sturznickel
J.
,
Schinke
T.
,
Amling
M.
,
Mundlos
S.
et al.
(
2018
)
A novel COL1A2 C-propeptide cleavage site mutation causing high bone mass osteogenesis imperfecta with a regional distribution pattern
.
Osteoporos. Int.
29
,
243
246
[PubMed]
53.
Cundy
T.
,
Dray
M.
,
Delahunt
J.
,
Hald
J.D.
,
Langdahl
B.
,
Li
C.
et al.
(
2018
)
Mutations that alter the carboxy-terminal-propeptide cleavage site of the chains of type I procollagen are associated with a unique osteogenesis imperfecta phenotype
.
J. Bone Miner. Res.
33
,
1260
1271
[PubMed]
54.
Asharani
P.V.
,
Keupp
K.
,
Semler
O.
,
Wang
W.
,
Li
Y.
,
Thiele
H.
et al.
(
2012
)
Attenuated BMP1 function compromises osteogenesis, leading to bone fragility in humans and zebrafish
.
Am. J. Hum. Genet.
90
,
661
674
[PubMed]
55.
Hoyer-Kuhn
H.
,
Semler
O.
,
Schoenau
E.
,
Roschger
P.
,
Klaushofer
K.
and
Rauch
F.
(
2013
)
Hyperosteoidosis and hypermineralization in the same bone: bone tissue analyses in a boy with a homozygous BMP1 mutation
.
Calcif. Tissue Int.
93
,
565
570
[PubMed]
56.
Martinez-Glez
V.
,
Valencia
M.
,
Caparros-Martin
J.A.
,
Aglan
M.
,
Temtamy
S.
,
Tenorio
J.
et al.
(
2012
)
Identification of a mutation causing deficient BMP1/mTLD proteolytic activity in autosomal recessive osteogenesis imperfecta
.
Hum. Mutat.
33
,
343
350
[PubMed]
57.
Syx
D.
,
Guillemyn
B.
,
Symoens
S.
,
Sousa
A.B.
,
Medeira
A.
,
Whiteford
M.
et al.
(
2015
)
Defective proteolytic processing of fibrillar procollagens and prodecorin due to biallelic BMP1 mutations results in a severe, progressive form of osteogenesis imperfecta
.
J. Bone Miner. Res.
30
,
1445
1456
[PubMed]
58.
Mizuno
M.
,
Fujisawa
R.
and
Kuboki
E.
(
2000
)
The effect of carboxyl-terminal propeptide of type I collagen (C-propeptide) on collagen synthesis of preosteoblasts and osteoblasts
.
Calcif. Tissue Int.
67
,
391
399
[PubMed]
59.
Aycock
R.S.
,
Raghow
R.
,
Stricklin
G.P.
,
Seyer
J.M.
and
Kang
A.H.
(
1986
)
Post-transcriptional inhibition of collagen and fibronectin synthesis by a synthetic homolog of a portion of the carboxyl-terminal propeptide of human type I collagen
.
J. Biol. Chem.
261
,
14355
14360
[PubMed]
60.
Wu
C.H.
,
Walton
C.M.
and
Wu
G.Y.
(
1991
)
Propeptide-mediated regulation of procollagen synthesis in IMR-90 human lung fibroblast cell cultures
.
J. Biol. Chem.
266
,
2983
2987
[PubMed]
61.
Wang
Y.
,
Azais
T.
,
Robin
M.
,
Vallee
A.
,
Catania
C.
,
Legriel
P.
et al.
(
2012
)
The predominant role of collagen in the nucleation, growth, structure and orientation of bone apatite
.
Nat. Mater.
11
,
724
733
[PubMed]
62.
Landis
W.J.
and
Jacquet
R.
(
2013
)
Association of calcium and phosphate ions with collagen in the mineralization of vertebrate tissues
.
Calcif. Tissue Int.
93
,
329
337
[PubMed]
63.
Eyre
D.R.
and
Weis
M.A.
(
2013
)
Bone collagen: new clues to its mineralization mechanism from recessive osteogenesis imperfecta
.
Calcif. Tissue Int.
93
,
338
347
[PubMed]
64.
Nudelman
F.
,
Pieterse
K.
,
George
A.
,
Bomans
P.H.
,
Friedrich
H.
,
Brylka
L.J.
et al.
(
2010
)
The role of collagen in bone apatite formation in the presence of hydroxyapatite nucleation inhibitors
.
Nat. Mater.
9
,
1004
1009
[PubMed]
65.
Hunter
G.K.
,
Hauschka
P.V.
,
Poole
A.R.
,
Rosenberg
L.C.
and
Goldberg
H.A.
(
1996
)
Nucleation and inhibition of hydroxyapatite formation by mineralized tissue proteins
.
Biochem. J.
317
,
59
64
[PubMed]
66.
Palmieri
D.
,
Camardella
L.
,
Ulivi
V.
,
Guasco
G.
and
Manduca
P.
(
2000
)
Trimer carboxyl propeptide of collagen I produced by mature osteoblasts is chemotactic for endothelial cells
.
J. Biol. Chem.
275
,
32658
32663
[PubMed]
67.
Palmieri
D.
,
Poggi
S.
,
Ulivi
V.
,
Casartelli
G.
and
Manduca
P.
(
2003
)
Pro-collagen I COOH-terminal trimer induces directional migration and metalloproteinases in breast cancer cells
.
J. Biol. Chem.
278
,
3639
3647
[PubMed]
68.
Palmieri
D.
,
Astigiano
S.
,
Barbieri
O.
,
Ferrari
N.
,
Marchisio
S.
,
Ulivi
V.
et al.
(
2008
)
Procollagen I COOH-terminal fragment induces VEGF-A and CXCR4 expression in breast carcinoma cells
.
Exp. Cell Res.
314
,
2289
2298
[PubMed]
69.
Visigalli
D.
,
Palmieri
D.
,
Strangio
A.
,
Astigiano
S.
,
Barbieri
O.
,
Casartelli
G.
et al.
(
2009
)
The carboxyl terminal trimer of procollagen I induces pro-metastatic changes and vascularization in breast cancer cells xenografts
.
BMC Cancer
9
,
59
[PubMed]
70.
Davies
D.
,
Tuckwell
D.S.
,
Calderwood
D.A.
,
Weston
S.A.
,
Takigawa
M.
and
Humphries
M.J.
(
1997
)
Molecular characterisation of integrin-procollagen C-propeptide interactions
.
Eur. J. Biochem.
246
,
274
282
[PubMed]
71.
Lamandé
S.R.
and
Bateman
J.F.
(
1999
)
Procollagen folding and assembly: the role of endoplasmic reticulum enzymes and molecular chaperones
.
Semin. Cell Dev. Biol.
10
,
455
464
[PubMed]
72.
Rosini
S.
,
Pugh
N.
,
Bonna
A.M.
,
Hulmes
D.J.S.
,
Farndale
R.W.
and
Adams
J.C.
(
2018
)
Thrombospondin-1 promotes matrix homeostasis by interacting with collagen and lysyl oxidase precursors and collagen cross-linking sites
.
Sci. Signal.
11
,
[PubMed]
73.
Salza
R.
,
Peysselon
F.
,
Chautard
E.
,
Faye
C.
,
Moschcovich
L.
,
Weiss
T.
et al.
(
2014
)
Extended interaction network of procollagen C-proteinase enhancer-1 in the extracellular matrix
.
Biochem. J.
457
,
137
149
[PubMed]
74.
Kalamajski
S.
,
Bihan
D.
,
Bonna
A.
,
Rubin
K.
and
Farndale
R.W.
(
2016
)
Fibromodulin interacts with collagen cross-linking sites and activates lysyl oxidase
.
J. Biol. Chem.
291
,
7951
7960
[PubMed]