Characterization of novel thermophilic alpha-glucosidase from Bifidobacterium longum

In this study, the gene encoding α-glucosidase from Bifidobacterium longum subsp. longum JCM1217 (BLAG) was cloned and expressed in Escherichia coli. The amino acid sequence alignment demonstrated that BLAG belongs to glycoside hydrolase (GH) family 13. The optimal temperature for enzyme activity was 75°C; about 80% of the catalytic activity was lost at 50°C, which is very unusual for enzymes from the Bifidobacterium genus. In the presence of 5mM of Co²⁺ and Ca²⁺, enzyme activity was reduced to 47% and 48%, respectively. Furthermore, BLAG lost catalytic activity following the addition of 5mM of Fe²⁺ ion. The BLAG enzyme was able to hydrolyze α-1,2, α-1,3, α-1,4, and α-1,6 glycosidic O-linkages and liberated glucose from the non-reducing end of substrates. The kinetic study revealed that among the maltooligosaccharides, BLAG showed the highest k_cat/K_m value to maltotriose (G3), and had relatively low k_cat/K_m values on long-chain maltooligosaccharides. This is the first report describing the production of a thermophilic α-glucosidase from the Bifidobacterium genus.