Functional characterization and site-directed mutagenesis of a novel UDP-glycosyltransferase from Panax japonicus var. major.

Ginsenosides R2 and F2 are key active components of Panax japonicus var. major which exhibit a wide range of pharmacological effects. However, few UDP-glycosyltransferases (UGTs) involved in Rh2 and F2 biosynthesis have been identified. In this study, 12 UGTs from Panax japonicus var. major were predicted and characterized. Among them, one UGT (PjvmUGT45) exhibited superior catalytic activities by catalyzing the C3 hydroxyl glycosylation of protopanaxadiol (PPD) and compound K to form Rh2 and F2, respectively. Especially, PjvmUGT45 showed certain substrate specificity and regional specificity at the C-3 sites of PPD-type ginsenosides. Site-directed mutagenesis showed that Gln334, His349, Ser354, and Asp373 were key residues for PjvmUGT45, and the K280A mutant highly improved its activity. Our results revealed the biosynthetic mechanism of ginsenosides in Panax japonicus var. major, providing a novel alternative UGT for ginsenoside Rh2 production by synthetic biological methods.