Fragrant Venezuelaenes A and B with A 5–5–6–7 Tetracyclic Skeleton: Discovery, Biosynthesis, and Mechanisms of Central Catalysts

A cryptic terpenoid biosynthetic gene cluster ven was characterized from the model actinomycetic strain Streptomyces venezuelae ATCC 15439 through a genome mining approach. Silent gene activation and heterologous expression of ven led to the discovery of two diterpene metabolites venezuelaene A ( 1 ) and B ( 2, 5-oxo-venezuelaene A), both of which bear a 5–5–6–7 tetracyclic skeleton and show fragrance. A class I diterpene synthase VenA with an atypical 115 DSFVSD 120 motif was revealed to catalyze the cyclization of geranylgeranyl pyrophosphate (GGPP) generated by the GGPP synthase VenD, giving rise to 1 . The unique cyclization mechanism was elucidated by 13 C-tracer NMR experiments. The oxidative transformation of 1 into 2 was also characterized to be mediated by the cytochrome P450 enzyme VenC.