Overexpression and characterization of a glycoside hydrolase family 1 enzyme from Cellulosimicrobium cellulans sp. 21 and its application for minor ginsenosides production

Abstract

A novel β-glucosidase gene (ccbgl1a) was cloned from the ginsenosides-transforming strain Cellulosimicrobium cellulans sp. 21. This enzyme was overexpressed in Escherichia coli, the recombinant β-glucosidase (CcBgl1A) containing N-terminal His-tag was sufficiently purified by nickel metal affinity chromatography with purification factor of 1.9-fold and specific activity of 31.5U/mg. The molecular mass of recombinant CcBgl1A was estimated to be approximately 46kDa. CcBgl1A exhibited optimal activity at 35°C and pH 5.5. However, above 40°C, the enzyme stability significantly decreased. The enzyme showed high bioconversion ability on protopanaxadiol-type ginsenosides mixture (PPDGM), which could hydrolyze the outer C-3 glucose moieties of ginsenosides Rb1, Rb2, Rc and Rd into the rare ginsenosides Gypenoside XVII (Gyp XVII), compound O, ginsenoside Mb and ginsenoside F2. Scaled-up production using 1g of the PPDGM resulted in 292mg Gyp XVII, 134mg CO, 184mg Mb, and 62mg F2, with chromatographic purities. These results suggest that CcBgl1A would be potentially useful in the preparation of pharmacologically active minor ginsenosides Gyp XVII, CO, Mb and F2.