Substrate specificity of β-glucosidase from Gordonia terrae for ginsenosides and its application in the production of ginsenosides Rg₃, Rg₂, and Rh₁ from ginseng root extract

Abstract

A β-glucosidase from Gordonia terrae was cloned and expressed in Escherichia coli. The recombinant enzyme with a specific activity of 16.4 U/mg for ginsenoside Rb1 was purified using His-trap chromatography. The purified enzyme specifically hydrolyzed the glucopyranosides at the C-20 position in protopanaxadiol (PPD)-type ginsenosides and hydrolyzed the glucopyranoside at the C-6 or C-20 position in protopanaxatriol (PPT)-type ginsenosides. The reaction conditions for the high-level production of Rg3 from Rb1 by the enzyme were pH 6.5, 30°C, 20 mg/ml enzyme, and 4 mg/ml Rb1. Under these conditions, G. terrae β-glucosidase completely converted Rb1 and Re to Rg3 and Rg2, respectively, after 2.5 and 8 h, respectively. Moreover, the enzyme converted Rg1 to Rh1 at 1 h with a molar conversion yield of 82%. The enzyme at 10 mg/ml produced 1.16 mg/ml Rg3, 1.47 mg/ml Rg2, and 1.17 mg/ml Rh1 from Rb1, Re, and Rg1, respectively, in 10% (w/v) ginseng root extract at pH 6.5 and 30°C after 33 h with molar conversion yields of 100%, 100%, and 77%, respectively. The combined molar conversion yield of Rg2, Rg3, and Rh1 from total ginsenosides in 10% (w/v) ginseng root extract was 68%. These above results suggest that this enzyme is useful for the production of ginsenosides Rg3, Rg2, and Rh1.

Keywords: Ginseng root extract; Ginsenosides Rg(3), Rg(2), and Rh(1); Gordonia terrae; Substrate specificity; β-Glucosidase.