Infection with schistosomes (blood flukes) can result in the debilitating disease schistosomiasis. These parasites survive in their host for many years, and we hypothesize that proteins on their tegumental surface, interacting with the host microenvironment, facilitate longevity. One such ectoenzyme — the nucleotide pyrophosphatase/phosphodiesterase SmNPP5 can cleave ADP (to prevent platelet aggregation) and NAD (likely preventing Treg apoptosis). A second tegumental ectoenzyme, the glycohydrolase SmNACE, also catabolizes NAD. Here, we undertake a comparative biochemical characterization of these parasite ectoenzymes. Both are GPI-linked and exhibit different optimal pH ranges. While SmNPP5 requires divalent cations, SmNACE does not. The KM values of the two enzymes for NAD at physiological pH differ: SmNPP5, KM = 340 µM ± 44; SmNACE, KM = 49 µM ± 4. NAD cleavage by each enzyme yields different products. SmNPP5 cleaves NAD to form nicotinamide mononucleotide (NMN) and AMP, whereas SmNACE cleaves NAD to generate nicotinamide (NAM) and adenosine diphosphate ribose (ADPR). Each enzyme can process the other's reaction product. Thus, SmNACE cleaves NMN (to yield NAM and ribose phosphate) and SmNPP5 cleaves ADPR (yielding AMP and ribose phosphate). Metabolomic analysis of plasma containing adult worms supports the idea that these cleavage pathways are active in vivo. We hypothesize that a primary function of SmNPP5 is to cleave NAD to control host immune cell function and a primary function of SmNACE is to cleave NMN to generate the vital nutrient nicotinamide (vitamin B3) for convenient uptake by the worms. Chemical inhibition of one or both ectoenzymes could upset worm metabolism and control schistosome infection.
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Cover Image
Cover Image
The cover image shows the crystal structure of AMPK a2b1g1 complexed with the pan activator MSG011. The inset surface representation details architecture of the MSG011 binding site, formed between the AMPK alpha-kinase domain (green) and beta-carbohydrate binding module (CBM, cyan). Explore more with Ovens and colleagues, “Structure-function analysis of the AMPK activator SC4 and identification of a potent pan AMPK activator” on pages 1181-1204.
NAD-catabolizing ectoenzymes of Schistosoma mansoni
Catherine S. Nation, Akram A. Da'Dara, Patrick J. Skelly; NAD-catabolizing ectoenzymes of Schistosoma mansoni. Biochem J 17 June 2022; 479 (11): 1165–1180. doi: https://doi.org/10.1042/BCJ20210784
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