Unusual (2,6)-bicyclo[3.1.1]heptane ring construction in fungal --bergamotene biosynthesis.

Bergamotenes are bicyclo[3.1.1]heptane sesquiterpenes found abundantly in plants and fungi. Known bergamotene derivatives all possess (2,6)-bergamotene backbone. In this study, two (+)--bergamotene derivatives ( and ) with unusual (2,6) configuration were isolated and elucidated from marine fungus sp. HLS206 The first (+)---bergamotene synthase NsBERS was characterized using genome mining and heterologous expression-based strategies. Based on homology search, we characterized another (+)---bergamotene synthase LsBERS from and an (+)--bisabolol synthase BcBOS from . We proposed that the cyclization mechanism of (+)--bergamotene involved - cyclization of left-handed helix farnesyl pyrophosphate by (6)-bisabolyl cation, which was supported by molecular docking. The biosynthesis-based volatiles (-) produced by heterologous fungal expression systems elicited significant electroantennographic responses of and , respectively, suggesting their potential in biocontrol of these pests. This work enriches diversity of sesquiterpenoids and fungal sesquiterpene synthases, providing insight into the enzymatic mechanism of formation of enantiomeric sesquiterpenes.