GuUGT, a glycosyltransferase from <i>Glycyrrhiza uralensis</i> , exhibits glycyrrhetinic acid 3- and 30-O-glycosylation

Abstract

<i>Glycyrrhiza uralensis</i> is a well-known herbal medicine that contains triterpenoid saponins as the predominant bioactive components, and these compounds include glycyrrhetinic acid (GA)-glycoside derivatives. Although two genes encoding UDP-glycosyltransferases (UGTs) that glycosylate these derivates have been functionally characterized in <i>G. uralensis</i>, the mechanisms of glycosylation by other UGTs remain unknown. Based on the available transcriptome data, we isolated a UGT with expression in the roots of <i>G. uralensis</i>. This UGT gene possibly encodes a glucosyltransferase that glycosylates GA derivatives at the 3-OH site. Biochemical analyses revealed that the recombinant UGT enzyme could transfer a glucosyl moiety to the free 3-OH or 30-COOH groups of GA. Furthermore, engineered yeast harbouring genes involved in the biosynthetic pathway for GA-glycoside derivates produced GA-3-<i>O</i>-β-D-glucoside, implying that the enzyme has GA 3-O-glucosyltransferase activity <i>in vivo</i>. Our results could provide a frame for understand the function of the UGT gene family, and also is important for further studies of triterpenoids biosynthesis in <i>G. uralensis</i>.