Fusion of Ginseng Farnesyl Diphosphate Synthase and Centella asciatica Squalene Synthase Involved in Triterpenoid Biosynthesis

Farnesyl diphosphate synthase (FPS) is a key enzyme in isoprenoid biosynthesis, generating farnesyl diphosphate as the central precursor for the broad classes of sesquiterpenoids and triterpenoids. On the one hand, cyclization of farnesyl diphosphate catalysed by various sesquiterpene synthases leads to structurally diverse sesquiterpenoids, while on the other, dimerization catalysed by squalene synthase (SQS) yields squalene as the first intermediate in the production of triterpenoids. To optimize triterpenoid production, the activities of an FPS generating farnesyl diphosphate and an SQS converting it should be coupled. Here, we constructed a fusion protein combining a ginseng FPS and a Centella asiatica SQS via a short peptide (Gly-Ser-Gly) linker. Heterologous expression in Escherichia coli resulted in a soluble fusion protein detected by SDS-PAGE. The fusion protein had both FPS and SQS activities, at approximately 94% and 71% of the single enzyme levels respectively. This novel fusion protein will serve as a valuable tool for genetic engineering of triterpenoid compounds, including saponins.