Characterization of UDP-Glycosyltransferase Involved in Biosynthesis of Ginsenosides Rg and Rb and Identification of Critical Conserved Amino Acid Residues for Its Function.

Ginsenosides attract great attention for their bioactivities. However, their contents are low, and many UDP-glycosyltransferases (UGTs) that play crucial roles in the ginsenoside biosynthesis pathways have not been identified, which hinders the biosynthesis of ginsenosides. In this study, we reported that one UDP-glycosyltransferase, UGTPg71A29, from Panax ginseng could glycosylate C20-OH of Rh and transfer a glucose moiety to Rd, producing ginsenosides Rg and Rb, respectively. Ectopic expression of UGTPg71A29 in Saccharomyces cerevisiae stably generated Rg and Rb under its corresponding substrate. Overexpression of UGTPg71A29 in transgenic cells of P. ginseng could significantly enhance the accumulation of Rg and Rb, with their contents of 3.2- and 3.5-fold higher than those in the control, respectively. Homology modeling, molecular dynamics, and mutational analysis revealed the key catalytic site, Gln283, which provided insights into the catalytic mechanism of UGTPg71A29. These results not only provide an efficient enzymatic tool for the synthesis of glycosides but also help achieve large-scale industrial production of glycosides.