Function and structure of GH13_31 α-glucosidase with high α-(1→4)-glucosidic linkage specificity and transglucosylation activity

alpha-Glucosidase hydrolyzes alpha-glucosides and transfers alpha-glucosyl residues to an acceptor through transglucosylation. In this study, GH13_31 alpha-glucosidase BspAG13_31A with high transglucosylation activity is reported in Bacillus sp. AHU2216 and biochemically and structurally characterized. This enzyme is specific to alpha-(1 -> 4)-glucosidic linkage as substrates and transglucosylation products. Maltose is the most preferred substrate. Crystal structures of BspAG13_31A wild-type for the substrate-free form and inactive acid/base mutant E256Q in complexes with maltooligosaccharides were solved at 1.6-2.5 angstrom resolution. BspAG13_31A has a catalytic domain folded by an (beta/alpha)(8)-barrel. In subsite +1, Ala200 and His203 on beta ->alpha loop 4 and Asn258 on beta ->alpha loop 5 are involved in the recognition of maltooligosaccharides. Structural basis for specificity of GH13_31 enzymes to alpha-(1 -> 4)-glucosidic linkage is first described.