De Novo Biosynthesis of a Polyene-Type Ginsenoside Precursor Dammaradienol in <i>Saccharomyces cerevisiae</i>

Typical dammarane-type ginsenosides are well-known tetracyclic triterpenoids with significant pharmacological effects including antitumor, cardiovascular protection, and neuroprotection. Polyene-type ginsenosides exhibit stronger biological activities than common ginsenosides; however, their contents are low, and most are converted from ginsenosides through a series of processing steps, resulting in higher preparation costs. In this study, a dammaradienol synthase, AarOSC20433, was identified for the first time from <i>Artemisia argyi</i> H. Lév. & Vaniot (<i>A. argyi</i>). The high-yielding squalene strain constructed in this study was used as the chassis strain. Yeast heterologous biosynthesis of the polyene-type ginsenoside precursor dammaradienol was achieved via metabolic engineering strategies, including optimization of the terpene supply, increase in copy number of AarOSC20433, and rational enzyme design. Eventually, through replenishment and batch fermentation, the titer of dammaradienol reached 1.037 g/L (4.3 mg/L/OD), laying a solid foundation for the construction of a polyene-type ginsenoside cell factory.