Engineering of critical enzymes and pathways for improved triterpenoid biosynthesis in yeast

Triterpenoids represent a diverse group of phytochemicals, widely distributed in the plant kingdom with many biological activities. Recently, the heterologous production of triterpenoids in Saccharomyces cerevisiae has been successfully implemented by introducing various triterpenoids biosynthetic pathways. By engineering related enzymes as well as yeast metabolism, the yield of various triterpenoids is significantly improved from milligram-scale per liter to gram-scale level per liter. This achievement demonstrates that engineering of critical enzymes is considered as a potential strategy to overcome the main hurdles of translation of these potent natural products into the industry. Here, we review strategies for designing enzymes to improve the yield of triterpenoids in S. cerevisiae, which is mainly separated into three aspects: 1. elevating the supply of the precursor - 2,3-oxidosqualene, 2. optimizing triterpenoid-involved reactions, 3. lowering the competition of the native sterol pathway. And then we provide challenges and prospects on further enhancing the triterpenoid production in S. cerevisiae.