Source
Department of Microbiology, University College Cork, Western Road, Cork, Ireland.
Abstract
Two alpha-glucosidase-encoding genes (agl1 and agl2) from Bifidobacterium breve UCC2003 were identified and characterized. Based on their similarity to characterized carbohydrate hydrolases, the Agl1 and Agl2 enzymes are both assigned to a subgroup of the glycosyl hydrolase family 13, the alpha-1,6-glucosidases (EC 3.2.1.10). Recombinant Agl1 and Agl2 into which a His(12) sequence was incorporated (Agl1(His) and Agl2(His), respectively) exhibited hydrolytic activity towards panose, isomaltose, isomaltotriose, and four sucrose isomers--palatinose, trehalulose, turanose, and maltulose--while also degrading trehalose and, to a lesser extent, nigerose. The preferred substrates for both enzymes were panose, isomaltose, and trehalulose. Furthermore, the pH and temperature optima for both enzymes were determined, showing that Agl1(His) exhibits higher thermo and pH optima than Agl2(His). The two purified alpha-1,6-glucosidases were also shown to have transglycosylation activity, synthesizing oligosaccharides from palatinose, trehalulose, trehalose, panose, and isomaltotriose.