Licorice Triterpenoids artificially synthesized by Saccharomyces cerevisiae

Triterpenoids are a highly diverse group of natural products and used particularly as medicine. Here, a strategy combining stepwise metabolic engineering and transcriptional control was developed to strengthen triterpenoid biosynthesis in Saccharomyces cerevisiae. Consequently, efficient biosynthetic pathways for producing ß-amyrin and glycyrrhetinic acid, a commercially valuable compounds and precursors of triterpenoids, were constructed through expressing a plant-derived ß-amyrin and glycyrrhetinic acid synthase. Introducing a heterologous squalene monooxygenase greatly dragged intermediate metabolite squalene toward ß-amyrin and glycyrrhetinic acid. Increasing squalene pool by overexpressing IPP isomerase, FPP and squalene synthase further enhanced ß-amyrin and glycyrrhetinic acid synthesis of 49 folds and 21 folds. Through reconstructing the promoters with the binding site of transcription factor UPC2, directed transcriptional regulation on engineered pathway was availably achieved, resulting in ß-amyrin titer increased by 65 folds. Using ethanol fed-batch fermentation, ß-amyrin titer was finally improved up to 159 mg/L with a yield of 16.30 mg/g dry cell, almost 185 and 232 and folds of the initially engineered strain respectively.