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
• Main Authors: Yuegui Chen, Qin Yan, Yunheng Ji, Xue Bai, Desen Li, Rongfang Mu, Kai Guo, Minjie Yang, Yang Tao, Jonathan Gershenzon, Yan Liu, Shenghong Li
• Format: Article
• Language: English
• Published: Elsevier 2023-11-01
• Subjects: Paris polyphylla var. yunnanensis; Steroidal saponins; Glycosyltransferases; Sugar chain elongation; Antifungal activity
• Online Access: http://www.sciencedirect.com/science/article/pii/S221138352300196X

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.