Unraveling the serial glycosylation in the biosynthesis of steroidal saponins in the medicinal plant Paris polyphylla and their antifungal action

• Published in: Acta pharmaceutica Sinica. B 2023-11, Vol.13 (11), p.4638-4654
• Main Authors: Chen, Yuegui, Yan, Qin, Ji, Yunheng, Bai, Xue, Li, Desen, Mu, Rongfang, Guo, Kai, Yang, Minjie, Tao, Yang, Gershenzon, Jonathan, Liu, Yan, Li, Shenghong
• Format: Article
• Language: English
• Subjects: Antifungal activity; Glycosyltransferases; Original; Paris polyphylla var. yunnanensis; Steroidal saponins; Sugar chain elongation
• ISSN: 2211-3835; 2211-3843
• DOI: 10.1016/j.apsb.2023.05.033

Sugar–sugar glycosyltransferases play important roles in constructing complex and bioactive saponins. Here, we characterized a series of UDP-glycosyltransferases responsible for biosynthesizing the branched sugar chain of bioactive steroidal saponins from a widely known medicinal plant Paris polyphylla var. yunnanensis. Among them, a 2′-O-rhamnosyltransferase and three 6′-O-glucosyltrasferases catalyzed a cascade of glycosylation to produce steroidal diglycosides and triglycosides, respectively. These UDP-glycosyltransferases showed astonishing substrate promiscuity, resulting in the generation of a panel of 24 terpenoid glycosides including 15 previously undescribed compounds. A mutant library containing 44 variants was constructed based on the identification of critical residues by molecular docking simulations and protein model alignments, and a mutant UGT91AH1Y187A with increased catalytic efficiency was obtained. The steroidal saponins exhibited remarkable antifungal activity against four widespread strains of human pathogenic fungi attributed to ergosterol-dependent damage of fungal cell membranes, and 2′-O-rhamnosylation appeared to correlate with strong antifungal effects. The findings elucidated the biosynthetic machinery for their production of steroidal saponins and revealed their potential as new antifungal agents. Six UDP-glycosyltransferases involved in the biosynthesis of steroidal saponins in Paris polyphylla var. yunnanensis were characterized. The potential of steroidal saponins as antifungal agents was disclosed. [Display omitted]