Identification and Characterization of a Novel Terrabacter ginsenosidimutans sp. nov. β-Glucosidase That Transforms Ginsenoside Rb1 into the Rare Gypenosides XVII and LXXV

Abstract

ABSTRACT A new β-glucosidase from a novel strain of Terrabacter ginsenosidimutans (Gsoil 3082 T ) 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 K m values of 4.2 ± 0.8 and 0.14 ± 0.05 mM and V max values of 100.6 ± 17.1 and 329 ± 31 μmol·min −1 ·mg of protein −1 against p -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.