Structural highlights
Publication Abstract from PubMedGlycoside hydrolase family 99 (GH99) was created to categorize sequence-related glycosidases possessing endo-alpha-mannosidase activity: the cleavage of mannosidic linkages within eukaryotic N-glycan precursors (Glc1-3 Man9 GlcNAc2 ), releasing mono-, di- and triglucosylated-mannose (Glc1-3 -1,3-Man). GH99 family members have recently been implicated in the ability of Bacteroides spp., present within the gut microbiota, to metabolize fungal cell wall alpha-mannans, releasing alpha-1,3-mannobiose by hydrolysing alphaMan-1,3-alphaMan-->1,2-alphaMan-1,2-alphaMan sequences within branches off the main alpha-1,6-mannan backbone. We report the development of a series of substrates and inhibitors, which we use to kinetically and structurally characterise this novel endo-alpha-1,2-mannanase activity of bacterial GH99 enzymes from Bacteroides thetaiotaomicron and xylanisolvens. These data reveal an approximate 5 kJ mol-1 preference for mannose-configured substrates in the -2 subsite (relative to glucose), which inspired the development of a new inhibitor, alpha-mannopyranosyl-1,3-isofagomine (ManIFG), the most potent (bacterial) GH99 inhibitor reported to date. X-ray structures of ManIFG or a substrate in complex with wild-type or inactive mutants, respectively, of B. xylanisolvens GH99 reveal the structural basis for binding to D-mannose- rather than D-glucose-configured substrates. Structural and Kinetic Dissection of the endo-alpha-1,2-Mannanase Activity of Bacterial GH99 Glycoside Hydrolases from Bacteroides spp.,Hakki Z, Thompson AJ, Bellmaine S, Speciale G, Davies GJ, Williams SJ Chemistry. 2014 Dec 8. doi: 10.1002/chem.201405539. PMID:25487964[1] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. References
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