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 L354 M 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.