5a7v

Publication Abstract from PubMed

The depolymerization of complex glycans is an important biological process that is of considerable interest to environmentally relevant industries. beta-mannose is a major component of plant structural polysaccharides and eukaryotic N-glycans. These linkages are primarily cleaved by glycoside hydrolases, although a family of glycoside phosphorylases, GH130, have also been shown to target beta-1,2 and beta-1,4 mannosidic linkages. In these phosphorylases bond cleavage was mediated by a single displacement reaction in which phosphate functions as the catalytic nucleophile. A cohort of GH130 enzymes, however, lack the conserved basic residues that bind the phosphate nucleophile, and it was proposed that these enzymes function as glycoside hydrolases. Here we show that two Bacteroides enzymes, BT3780 and BACOVA03624, which lack the phosphate binding residues are indeed betamannosidases that hydrolyse beta-1,2-mannosidic linkages through an inverting mechanism. As the genes encoding these enzymes are located in genetic loci that orchestrate the depolymerisation of yeast alpha-mannans, it is likely that the two enzymes target the beta-1,2-mannose residues that cap the glycan produced by Candida albicans. The crystal structure of BT3780 in complex with mannose bound in the -1 and +1 subsites showed a pair of glutamates, Glu227 and Glu268 hydrogen bond to O1 of alpha-mannose, and either of these residues may function as the catalytic base. The candidate catalytic acid and the other residues that interact with the active site mannose are conserved in both GH130 mannoside phosphorylases and beta-1,2-mannosidases. Functional phylogeny identified a conserved lysine, Lys199 in BT3780, as a key specificity determinant for beta-1,2-mannosidic linkages.

The GH130 family of mannoside phosphorylases contains glycoside hydrolases that target beta-1,2 mannosidic linkages in Candida mannan.,Cuskin F, Basle A, Ladeveze S, Day AM, Gilbert HJ, Davies GJ, Potocki-Veronese G, Lowe EC J Biol Chem. 2015 Aug 18. pii: jbc.M115.681460. PMID:26286752^[1]

From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.