18α-Glycyrrhizin(18α-GL)is an oleanane-type saponin.18α-GL is less polar and more lipophilic than its diastereomer 18β-GL.Its stronger anti-toxic and anti-inflammatory effects and higher liver targeting make 18α-GL a major drug ingredient in the field of liver protection.However,the current preparation method of 18α-GL is highly polluting and has low efficiency.Therefore,there is an urgent need to develop a green and simple method to synthesize 18α-GL.Glycosyltransferases were heterologously expressed in yeast cells.Through whole-cell catalysis,glycosyltransferases cGuCSyGT was identified as being able to catalyze the specific synthesis of 18α-glycyrrhetinic acid 3-O-monoglucuronide(18α-GAMG)from 18α-glycyrrhetinic acid(18α-GA)and GgUGT1 was identified as being able to catalyze the specific synthesis of 18α-glycyrrhizin(18α-GL)from 18α-GAMG.We further employed protein structure prediction and molecular dynamics simulation to explore the reason why cGuCSyGT has lower catalytic activity for 18α-GA than 18β-GA.Finally,an optimal process for yeast catalytic synthesis of 18α-GAMG and 18α-GL was constructed by optimizing various parameters,including substrate addition concentration,chassis host cells,substrate addition time,catalytic time,medium component addition and substrate solvent.Thus,the production of 18α-GAMG and 18α-GL reached(36.38±1.87)mg/L and(39.32±0.75)mg/L,respectively.This research achieved the microbial catalytic synthesis of 18α-GAMG and 18α-GL,which will provide a theoretical basis and technical support for the total microbial synthesis of 1 8α-GL.
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