Identification of a Novel Glycosyltransferase CaUGT Specifically Targeting the C-30 Position of Glycyrrhetinic Acid and Development of an Efficient Enzymatic Biotransformation System.

Abstract

Glycyrrhetinic acid (GA) is a major bioactive ingredient of licorice with extensive pharmacological functions, while its strong hydrophobicity and low permeability severely restrict practical application. Enzymatic glycosylation serves as a mild method to enhance GA solubility and bioactivity, yet few reported glycosyltransferases can specifically modify the C30 carboxyl group of GA. In this study, a novel glycosyltransferase gene CaUGT was identified and cloned from Cardamine amara subsp. amara. The recombinant GST-CaUGT achieved optimal expression under 2% dextrin, 0.2 mM IPTG and 25 °C induction temperature. The enzyme exhibited the highest activity at 25 °C and pH 6.0, with high thermal and pH stability. It displayed a strict regioselectivity toward the GA C30 carboxyl, with a Km of 0.0501 mmol/L and a kcat of 52.3 s-1·M-1. A constructed two-enzyme cascade system produced 452.8 mg/L GA 30-O-glucoside with a space-time yield of 600.9 mg/L/h, providing an efficient biocatalytic route for triterpenoid carboxyl glycosylation.