Biosynthesis of fungal drimane-type sesquiterpene esters.
Drimane-type sesquiterpenes exhibit various biological activities and are widely present in eukaryotes. Here, we completely elucidated the biosynthetic pathway of the drimane-type sesquiterpene esters isolated from Aspergillus calidoustus and we discovered that it involves a drimenol cyclase having the same catalytic function previously only reported in plants. Moreover, since many fungal drimenol derivatives possess a γ-butyrolactone ring, we clarified the functions of the cluster-associated cytochrome P450 and FAD-binding oxidoreductase discovering that these two enzymes are solely responsible for the formation of those structures. Furthermore, swapping of the enoyl-reductase domain in the identified polyketide synthase led to the production of metabolites containing various polyketide chains with different levels of saturations. These findings have deepened our understanding of how fungi synthesize drimane-type sesquiterpenes and the corresponding esters.