Enzymatic biosynthesis of novel bavachin glucosides via Bacillus UDP-glycosyltransferase

Abstract

A UDP-glycosyltransferase (YjiC) from Bacillus licheniformis was exploited for the glycosylation of bavachin. The in vitro glycosylation reaction generated three novel bavachin glucosides, which were structurally characterized as bavachin-4′-O-β-d-glucopyranoside (1), bavachin-7-O-β-d-glucopyranoside (2), and bavachin-4′,7-di-O-β-d-glucopyranoside (3) based on spectroscopic techniques. To enhance product yield, the reaction time, buffer pH, and UDP-glucose concentration were optimized. The water-solubility of compounds 1, 2, and 3 was approximately 5.18, 56.22, and 84.17 times higher than that of bavachin, respectively. In addition, compounds 1-3 displayed the highest stability at pH 8.8 and were stable up to 70°C for 30min. Furthermore, the biological activities of bavachin and compounds 1-3 were assayed. Bavachin showed moderate cytotoxicity against four human cancer cell lines while the three glycosylation products displayed weak activity. The results demonstrate that the UDP-glycosyltransferase (YjiC) has the capacity to synthesis bavachin glucosides and that glycosylation of bavachin enhances its water-solubility and stability.