Scientific research on elucidation of terpene-cyclic reactions in the biosynthesis of bioactive microbial terpenoids.

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(1)We isolated (+)-cyatha-3,12-diene from an erinacine-producing fungus, and confirmed its stereostructure by semi-synthesis from erinacine P. The cyathane hydrocarbon could be obtained from GGDP by the cell-free system. From a fusicoccin-mass-producing fungus we isolated (+)-δ-araneosene as the presumed bicyclic hydrocarbon intermediate. (+)-Fusicocca-3(16),10(14)-diene was also isolated and its identification suggested the presence of a new fusicoccenyl cation in the biosynthetic pathway. (2)We identified two gene clusters responsible for diterpene biosynthesis by chromosome waling from GGDP synthase genes from Phomopsis amygdali. The gene clusters led us to successful isolation and characterization of two cDNAs encoding diterpene cyclases. (3)The gene cluster for aphidicolin biosynthesis has been identified by PCR-based genome walking using reported sequence of cDNA coding the diterpene cyclase. Based on non-enzymatic cyclization under various conditions and molecular orbital calculations, cyclization mechanism for construction of aphidicolane skeleton was proposed. (4)We have cloned two diterpene cyclase genes essential for biosynthesis of terpentecin. By using recombinant enzymes, it was revealed that one enzyme converted GGDP into a cyclized intermediate (terpentedienol diphosphate), and then it was transformed into terpentetriene by the other enzyme. (5)By using the site-specific mutants and the substrate analogs, we clearly demonstrated that the steric bulk size of active site residues has an important role in determining the folding conformation of squalene substrate during the polycyclization cascade.