Triterpenoid saponins are widely distributed natural products with diverse pharmacological activities. They are synthesized through the attachment of sugar moieties to the triterpenoid skeleton, a process catalyzed by UDP-glycosyltransferases (UGTs). However, the UGTs responsible for the glycosylation of many triterpenoids remain unidentified, primarily due to the limited understanding of sequence–function relationships. Here, we systematically analyzed and characterized UGTs in Glycyrrhiza glabra, revealing that UGT73F/P enzymes mediate the primary glycosylation of triterpenoids with distinctive regioselectivity. This finding was further supported by a kingdom-wide mining effort and selective characterization among 286 UGT73F/P enzymes from 167 plant species, covering 54 families. In addition, we found that UGT73F and UGT73P enzymes were specific to legume species. Finally, we identified a K-region within the enzyme active site that governs the differentiated function of UGT73F/P enzymes. Our study highlights the great potential of UGT73F/P enzymes for precise triterpenoid glycosylation and expands the enzymatic toolkit for triterpenoid saponin biosynthesis.
Zhang et al. (Mon,) studied this question.