Cloning and characterization of a novel recombinant multifunctional glycoside hydrolase β-D-xylosidase/α-L-arabinopyranosidase/β-glucosidase from Bifidobacterium adolescentis and its application on the biotransformation of ginsenoside Rb3

β-D-xylosidase, an important glycoside hydrolase, hydrolyzes xylo-oligosaccharides to yield xylose and biotransforms specific saponins by cleaving β-xylose at the non-reducing end. It is extensively employed in renewable resources, including fuels, food, and pharmaceuticals, as a xylanolytic enzyme. In this study, a 1197 bp β-xylosidase gene (BaXyl5B) derived from Bifidobacterium adolescentis was cloned and expressed in E. coli BL21. Following purification, the recombinant β-xylosidase exhibited a distinct band on SDS-PAGE; its molecular weight was determined to be 46.4 kDa. The optimal activity of BaXyl5B was observed at a pH of 6.0 and a temperature of 30 °C. Purified BaXyl5B demonstrated multifunctional activities involving p-nitrophenyl-β-D-xylopyranoside (pNPβXyl), p-nitrophenyl-α-L-arabinopyranoside (pNPαArap), and p-nitrophenyl-β-D-glucopyranoside (pNPβGlc). A significant finding of this study was that BaXyl5B exhibited high selectivity towards ginsenoside Rb3, which could hydrolyze xylose at the C-20 position of Rb3 to yield Rd and F2. Overall, this research explored a novel β-xylosidase, BaXyl5B, that could serve as a valuable biocatalyst for converting ginsenosides and synthesizing active glycosides and aglycones, making it a promising enzyme for further exploration and utilization.