Biocatalytic Production of Piceatannol-4′-O-Glucoside Using a Novel Glycosyltransferase SoUGT from Saponaria officinalis

Piceatannol is a natural stilbene polyphenol with promising bioactivities, but its poor water solubility and low bioavailability limit industrial applications. In this study, a novel UDP-dependent glycosyltransferase, SoUGT, was identified from Saponaria officinalis for regioselective glycosylation of piceatannol. SoUGT belongs to the UGT72 subfamily and contains the conserved PSPG (Plant Secondary Product Glycosyltransferase) motif typical of plant O-glycosyltransferases. Molecular docking analysis predicted several residues, including Tyr143, Val120, Ala121, and Val123, that may contribute to substrate binding and positioning. GST fusion significantly improved soluble expression and catalytic activity in Escherichia coli. The enzyme showed optimal activity at 50 °C and pH 8.5, with good thermal stability and solvent tolerance, predominantly producing piceatannol-4′-O-glucoside. To reduce UDP-glucose cost, a cellobiose-based regeneration system was developed. Under optimized conditions, the engineered strain produced 380.84 mg/L piceatannol-4′-O-glucoside within 48 h, achieving a 78.77% conversion rate.