Identification of a highly promiscuous glucosyltransferase from Penstemon barbatus for natural product glycodiversification

Glycosylation reactions mediated by UDP-glycosyltransferases (UGTs) are common post-modifications involved in plant secondary metabolism and significantly improve the solubility and bioactivity of aglycones. Penstemon barbatus is rich in phenylethanoid glycosides (PhGs), such as echinacoside and verbascoside. In this study, a promiscuous glycosyltransferase UGT84A95 was identified from P. barbatus. In vitro enzyme assays showed that UGT84A95 catalyzed the glucosylation of the phenol hydroxyl group of PhGs efficiently as well as other structurally diverse phenolic glycosides, including flavonoids, terpenoids, stilbene glycosides, coumarins, and simple polyphenols. By using UGT84A95, 12 glycosylated products were prepared and structurally identified by NMR spectroscopy, among which 7 are new compounds. These findings suggest that UGT84A95 could be a potential biocatalyst to synthesize multi-glycosylated glycosides.