Purification and characterization of a novel β-glucuronidase precisely converts glycyrrhizin to glycyrrhetinic acid 3-O-mono-β-D-glucuronide from plant endophytic Chaetomium globosum DX-THS3

Glycyrrhetinic acid monoglucuronide (GAMG) is an innovative functional sweetener with higher sweetness and stronger pharmacological activity than glycyrrhizin (GL). A novel S-glucuronidase (cg-GUS) was firstly screened from plant endophytic fungus Chaetomium globosum DX-THS3. The cg-GUS demonstrated the specify and highly transform glycyrrhizin (GL) to generate GAMG, and the maximum activity of S-glucuronidase at 45 degrees C and pH 6.0, displaying excellent thermostability and pH-stability. The K-m and V-max values of cg-GUS were 0.134 mM and 236.42 mM/min/mg, respectively, which showed the high chemical bond selectivity and biotransformation effi-ciency of cg-GUS. Meanwhile, the cg-GUS gene (1896 bp) was analyzed, and Gly-345, Ser-539, Gly-563, Ala-579, Ser-581 and Glu-619 in GH2 catalytic domain of cg-GUS are potential mutation position for result in high -efficient and substrate-specify of cg-GUS. Our results were indicated that cg-GUS is a biocatalyst for production of GAMG and potent application in food and medicinal industry. (C) 2020 Elsevier B.V. All rights reserved.