Identification and Characterization of a Promiscuous Pentacyclic Triterpenoid O-glycosyltransferase from Phytolacca americana

Glycosyltransferases (GTs) are key enzymes in the glycosylation of plant secondary metabolites, primarily catalyzing the transfer of a sugar moiety from an activated donor to a specific acceptor molecule. Triterpenoid saponins, an abundant and diverse group of natural products, are composed of triterpenoid aglycones and one or more sugar chains, under the catalysis of GTs. Phytolacca Radix is a traditional Chinese medicine containing over 40 triterpenoid saponins with pharmacological values. However, the identification of glycosyltransferases related to triterpenoid saponin synthesis from Phytolacca species remains scarce. In this study, a novel glycosyltransferase, PamUGT, was identified from Phytolacca americana. PamUGT exhibits catalytic activity toward 28-/30-COOH of pentacyclic triterpenoids, and it exhibits a preference for the C-30 position when both carboxyl groups are available. To our knowledge, PamUGT is the first glycosyltransferase identified in Phytolacca species that can catalyze triterpenoids. Further analysis of substrate specificity revealed that PamUGT catalyzes the glycosylation of a wide range of compounds, including triterpenoids, flavonoids, diterpenoids, alkaloids, and phenolic acids. Our findings identify a highly promiscuous glycosyltransferase, offering a valuable enzymatic tool for modifying diverse natural products.