Spiroluchuene A Synthase: A Cyclase from Aspergillus luchuensis Forming a Spirotetracyclic Diterpene

The diterpene synthase AlTS was identified from Aspergillus luchuensis. AlTS catalyses the formation of the diterpene hydrocarbon spiroluchuene A, which exhibits a novel skeleton characterised by a spirocyclic ring system. The cyclisation mechanism towards this compound was elucidated through isotopic labelling experiments in conjunction with DFT calculations and metadynamic simulations. The biosynthetic intermediate luchudiene, besides the derivative spiroluchuene B, was captured from an enzyme variant obtained through site‐directed mutagenesis. With its 10‐membered ring luchudiene is structurally related to germacrenes and can undergo a Cope rearrangement to luchuelemene. A diterpene synthase for spiroluchuene A exhibiting a novel skeleton was discovered from Aspergillus luchuensis. Enzyme engineering through site‐directed mutagenesis allowed for the isolation of spiroluchuene B and the intermediate spiroluchuene. The enzyme mechanism was deeply studied through isotopic labelling experiments, DFT calculations and metadynamic simulations. The thermal reactions of luchudiene were studied.