Bioconversion of ginsenosides Rb1, Rb2, Rc and Rd by novel beta-glucosidase hydrolyzing outer 3-O glycoside from Sphingomonas sp. 2F2: Cloning, expression, and enzyme characterization

Abstract

A new β-glucosidase gene (bglSp) was cloned from the ginsenoside converting Sphingomonas sp. strain 2F2 isolated from the ginseng cultivating filed. The bglSp consisted of 1344bp (447 amino acid residues) with a predicted molecular mass of 49,399Da. A BLAST search using the bglSp sequence revealed significant homology to that of glycoside hydrolase superfamily 1. This enzyme was overexpressed in Escherichia coli BL21 (DE3) using a pET21-MBP (TEV) vector system. Overexpressed recombinant enzymes which could convert the ginsenosides Rb 1, Rb 2, Rc and Rd to the more pharmacological active rare ginsenosides gypenoside XVII, ginsenoside C-O, ginsenoside C-Mc 1 and ginsenoside F 2, respectively, were purified by two steps with Amylose-affinity and DEAE-Cellulose chromatography and characterized. The kinetic parameters for β-glucosidase showed the apparent K m and V max values of 2.9±0.3mM and 515.4±38.3μmolmin -1mg of protein -1 against p-nitrophenyl-β-d-glucopyranoside. The enzyme could hydrolyze the outer C3 glucose moieties of ginsenosides Rb 1, Rb 2, Rc and Rd into the rare ginsenosides Gyp XVII, C-O, C-Mc 1 and F 2 quickly at optimal conditions of pH 5.0 and 37°C. A little ginsenoside F 2 production from ginsenosides Gyp XVII, C-O, and C-Mc 1 was observed for the lengthy enzyme reaction caused by the side ability of the enzyme.