Function and structure of GH13₃1 α‐glucosidase with high α‐ (1→4) ‐glucosidic linkage specificity and transglucosylation activity

α-Glucosidase hydrolyzes α-glucosides and transfers α-glucosyl residues to an acceptor through transglucosylation. In this study, GH13₃1 α-glucosidase BspAG13₃1A with high transglucosylation activity is reported in Bacillus sp. AHU2216 and biochemically and structurally characterized. This enzyme is specific to α- (1→4) -glucosidic linkage as substrates and transglucosylation products. Maltose is the most preferred substrate. Crystal structures of BspAG13₃1A wild-type for the substrate-free form and inactive acid/base mutant E256Q in complexes with maltooligosaccharides were solved at 1. 6-2. 5 Å resolution. BspAG13₃1A has a catalytic domain folded by an (β/α) 8 -barrel. In subsite +1, Ala200 and His203 on β→α loop 4 and Asn258 on β→α loop 5 are involved in the recognition of maltooligosaccharides. Structural basis for specificity of GH13₃1 enzymes to α- (1→4) -glucosidic linkage is first described.