Identification and characterization of a novel Terrabacter ginsenosidimutans sp. nov. beta-glucosidase that transforms ginsenoside Rb1 into the rare gypenosides XVII and LXXV

Abstract

A new β-glucosidase from a novel strain of Terrabacter ginsenosidimutans (Gsoil 3082T) obtained from the soil of a ginseng farm was characterized, and the gene, bgpA (1,947 bp), was cloned in Escherichia coli. The enzyme catalyzed the conversion of ginsenoside Rb1 {3-O-[β-D-glucopyranosyl-(1-2)-β-D-glucopyranosyl]-20-O-[β-D- glucopyranosyl-(1-6)-β-D-glucopyranosyl]-20(S)-protopanaxadiol} to the more pharmacologically active rare ginsenosides gypenoside XVII {3-O-β-D- glucopyranosyl-20-O-[β-D-glucopyranosyl-(1-6)-β-D-glucopyranosyl] -20(S)-protopanaxadiol}, gypenoside LXXV {20-O-[β-D-glucopyranosyl-(1-6)- β-D-glucopyranosyl]-20(S)-protopanaxadiol}, and C-K [20-O-(β-D- glucopyranosyl)-20(S)-protopanaxadiol]. A BLAST search of the bgpA sequence revealed significant homology to family 3 glycoside hydrolases. Expressed in E. coli, β-glucosidase had apparent Km values of 4.2 ± 0.8 and 0.14 ± 0.05 mM and Vmax values of 100.6 ± 17.1 and 329 ± 31 (μmol · min-1 · mg of protein -1 againstp-nitrophenyl-β-D-glucopyranoside and Rb1, respectively. The enzyme catalyzed the hydrolysis of the two glucose moieties attached to the C-3 position of ginsenoside Rb1, and the outer glucose attached to the C-20 position at pH 7.0 and 37°C. These cleavages occurred in a defined order, with the outer glucose of C-3 cleaved first, followed by the inner glucose of C-3, and finally the outer glucose of C-20. These results indicated that BgpA selectively and sequentially converts ginsenoside Rb1 to the rare ginsenosides gypenoside XVII, gypenoside LXXV, and then C-K. Herein is the first report of the cloning and characterization of a novel ginsenoside-transforming β-glucosidase of the glycoside hydrolase family 3.