Identification and Characterization of a Mucilaginibacter sp. Strain QM49 β-Glucosidase and Its Use in the Production of the Pharmaceutically Active Minor Ginsenosides ( S )-Rh 1 and ( S )-Rg 2

Here, we isolated and characterized a new ginsenoside-transforming β-glucosidase (BglQM) fromMucilaginibacter sp. strain QM49 that shows biotransformation activity for various major ginsenosides. The gene responsible for this activity,bglQM , consists of 2,346 bp and is predicted to encode 781 amino acid residues. This enzyme has a molecular mass of 85.6 kDa. Sequence analysis of BglQM revealed that it could be classified into glycoside hydrolase family 3. The enzyme was overexpressed inEscherichia coli BL21(DE3) using a maltose binding protein (MBP)-fused pMAL-c2x vector system containing the tobacco etch virus (TEV) proteolytic cleavage site. Overexpressed recombinant BglQM could efficiently transform the protopanaxatriol-type ginsenosides Re and Rg1 into (S )-Rg2 and (S )-Rh1 , respectively, by hydrolyzing one glucose moiety attached to the C-20 position at pH 8.0 and 30°C. TheKm values forp -nitrophenyl-β-d -glucopyranoside, Re, and Rg1 were 37.0 ± 0.4 μM and 3.22 ± 0.15 and 1.48 ± 0.09 mM, respectively, and theV max values were 33.4 ± 0.6 μmol min−1 mg−1 of protein and 19.2 ± 0.2 and 28.8 ± 0.27 nmol min−1 mg−1 of protein, respectively. A crude protopanaxatriol-type ginsenoside mixture (PPTGM) was treated with BglQM, followed by silica column purification, to produce (S )-Rh1 and (S )-Rg2 at chromatographic purities of 98% ± 0.5% and 97% ± 1.2%, respectively. This is the first report of gram-scale production of (S )-Rh1 and (S )-Rg2 from PPTGM using a novel ginsenoside-transforming β-glucosidase of glycoside hydrolase family 3.