Characterization of a novel recombinant β-glucosidase from Sphingopyxis alaskensis that specifically hydrolyzes the outer glucose at the C-3 position in protopanaxadiol-type ginsenosides

A recombinant β-glucosidase from Sphingopyxis alaskensis with a specific activity of 233.3 U mg−1 was purified by His-trap chromatography. The native enzyme was a 206 kDa tetramer. The maximum enzyme activity was observed at pH 5.5 and 50 °C. However, above 40 °C, the enzyme stability significantly decreased. The enzyme hydrolyzed only the outer glucose at the C-3 position in protopanaxadiol-type ginsenosides without further hydrolysis. Because of the narrow substrate specificity, the enzyme completely converted ginsenosides Rb1, Rb2, Rc, and Rd as substrates to gypenoside XVII, compound O, compound Mc1, and F2, respectively, and it converted ginsenoside Rg3 to Rh2 with a molar conversion yield of 89%. These results suggest that the recombinant β-glucosidase from S. alaskensis is a potential producer of the rare ginsenosides gypenoside XVII, compound O, compound Mc1, F2, and Rh2. Among ginsenoside substrates, Rb1 was used for the high-level production of the rare ginsenoside gypenoside XVII. The optimum reaction conditions were pH 5.5, 40 °C, 0.5 mg ml−1 (116.7 U ml−1) enzyme, and 8.0 g l−1 ginsenoside Rb1. Under these conditions, 6.8 g l−1 gypenoside XVII was produced by the enzyme after 1 h with a molar conversion yield of 100% and a productivity of 6.8 g l−1 h−1.