Refactoring β-Amyrin synthesis in 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, an efficient biosynthetic pathway for producing β-amyrin, a commercially valuable compound and precursor of triterpenoids, was constructed through expressing a plant-derived β-amyrin synthase. Introducing a heterologous squalene monooxygenase greatly dragged intermediate metabolite squalene toward β-amyrin. Increasing squalene pool by overexpressing IPP isomerase, FPP, and squalene synthase further enhanced β-amyrin synthesis of 49-folds. Through reconstructing the promoters with the binding site of transcription factor UPC2, directed transcriptional regulation on engineered pathway was availably achieved, resulting in β-amyrin titer increased by 65-folds. Using ethanol fed-batch fermentation, β-amyrin titer was finally improved up to 138.80 mg/L with a yield of 16.30 mg/g dry cell, almost 185 and 232 and folds of the initially engineered strain, respectively.