From Monocyclization to Pentacyclization: A Versatile Plant Cyclase Produces Diverse Sesterterpenes with Anti‐Liver Fibrosis Potential

Abstract A prolific multi‐product sesterterpene synthase CbTPS1 is characterized from the medicinal Brassicaceae plant Capsella bursa‐pastoris. Twenty different sesterterpenes including 16 undescribed compounds, possessing 10 different mono‐/di‐/tri‐/tetra‐/penta‐carbocyclic skeletons, including the unique 15‐membered macrocyclic and 24(15→14)‐abeo‐capbuane scaffolds, are isolated and structurally elucidated from engineered Escherichia coli strains expressing CbTPS1. Site‐directed mutagenesis assisted by molecular dynamics simulations resulted in the variant L354M with up to 13.2‐fold increased sesterterpene production. These structurally diverse products suggest a comprehensive cyclization mechanism for plant sesterterpenes and provide compelling evidence for the initial cyclization of geranylfarnesyl diphosphate via a crucial 15‐membered monocyclic carbocation. The activities of these sesterterpenes against liver fibrosis is inferred from the inhibition of the transforming growth factor‐β/Smad signaling pathway and collagen synthesis. These findings greatly expand the chemical space and biological functions of sesterterpenes and provide new insights into the catalytic mechanism of terpene synthases.