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Publication Abstract from PubMed

Phenylethanoid glycosides (PhGs) are a group of important natural products found in a wide variety of medicinal plants, and are known to possess outstanding pharmacological properties. Uridine diphosphate (UDP) glycosyltransferase 79G15 (UGT79G15) from Rehmannia glutinosa‌ catalyzes the conversion of osmanthuside A to osmanthuside B, a key intermediate in the PhG biosynthetic pathway, via the formation of a (1-->3) glycosidic bond. In this study, we report the crystal structure of UGT79G15 in its apo form, UDP-bound form and, most importantly, its ternary complex form containing UDP and a mimic acceptor, forsythiaside A, in its active site. Structural and comparative analyses revealed that UGT79G15 has a unique 'funnel-shaped' acceptor-binding pocket with a small accessory cave sufficient to accommodate the 4'-hydroxycinnamoyl group of PhG, explaining the enzyme's regiospecificity for the 3'-OH of PhG. Further structural analysis and site-directed mutagenesis explored a number of variants of the enzyme and identified key residues that recognize and stabilize UDP-rhamnose and the sugar acceptor. Meanwhile, I204W, a point variant obtained in the process, was found to possess increased catalytic efficiency for osmanthuside A conversion, up to 2.2 times the efficiency of the wild type. This study provides mechanistic insights into the donor specificity and acceptor regioselectivity of PhG 1,3-rhamnosyltransferase and enriches structural information on plant UGTs.

Structural insights into the catalytic mechanism of the phenylethanoid glycoside rhamnosyltransferase UGT79G15 from Rehmannia glutinosa.,Ma R, Wei H, Zhuang Y, Wu Y, Li Z, Chen Y, Huang J, Yan X, Liu W, Liu T Plant Commun. 2025 Sep 25:101539. doi: 10.1016/j.xplc.2025.101539. PMID:41013894^[1]

From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.