Purification and characterization of highly branched α-glucan-producing enzymes from Paenibacillus sp. PP710.

Highly branched α-glucan molecules exhibit low digestibility for α-amylase and glucoamylase, and abundant in α-(1→3)-, α-(1→6)-glucosidic linkages and α-(1→6)-linked branch points where another glucosyl chain is initiated through an α-(1→3)-linkage. From a culture supernatant of Paenibacillus sp. PP710, we purified α-glucosidase (AGL) and α-amylase (AMY), which were involved in the production of highly branched α-glucan from maltodextrin. AGL catalyzed the transglucosylation reaction of a glucosyl residue to a nonreducing-end glucosyl residue by α-1,6-, α-1,4-, and α-1,3-linkages. AMY catalyzed the hydrolysis of the α-1,4-linkage and the intermolecular or intramolecular transfer of maltooligosaccharide like cyclodextrin glucanotransferase (CGTase). It also catalyzed the transfer of an α-1,4-glucosyl chain to a C3- or C4-hydroxyl group in the α-1,4- or α-1,6-linked nonreducing-end residue or the α-1,6-linked residue located in the other chains. Hence AMY was regarded as a novel enzyme. We think that the mechanism of formation of highly branched α-glucan from maltodextrin is as follows: α-1,6- and α-1,3-linked residues are generated by the transglucosylation of AGL at the nonreducing ends of glucosyl chains. Then AMY catalyzes the transfer of α-1,4-chains to C3- or C4-hydroxyl groups in the α-1,4- or α-1,6-linked residues generated by AGL. Thus the concerted reactions of both AGL and AMY are necessary to produce the highly branched α-glucan from maltodextrin.