Cyclopenase asqI

UniProtKB accession:  C8VJQ3

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UniProtKB description:  Cyclopenase; part of the gene cluster that mediates the biosynthesis of the aspoquinolone mycotoxins (PubMed:25251934, PubMed:30026518). Within the pathway, the cyclopenase asqI catalyzes the conversion of 4'-methoxycyclopenin into 4'-methoxyviridicatin (PubMed:30026518). Cyclopenin can also be converted into viridicatin by asqI (PubMed:30026518). The first step of the pathway is catalyzed by the nonribosomal peptide synthetase asqK that condenses anthranilic acid and O-methyl-L-tyrosine to produce 4'-methoxycyclopeptin. 4'-methoxycyclopeptin is then converted to 4'-methoxydehydrocyclopeptin by the ketoglutarate-dependent dioxygenase asqJ. AsqJ also converts its first product 4'-methoxydehydrocyclopeptin to 4'-methoxycyclopenin. The following conversion of 4'-methoxycyclopenin into 4'-methoxyviridicatin is catalyzed by the cyclopenase asqI. 4'-methoxyviridicatin is the precursor of quinolone natural products, and is further converted to quinolinone B. The prenyltransferase asqH1 then catalyzes the canonical Friedel-Crafts alkylation of quinolinone B with dimethylallyl cation to yield dimethylallyl quinolone, which is subjected to FAD-dependent dehydrogenation by the FAD-linked oxidoreductase asqF to yield conjugated aryl diene. The delta(3') double bond then serves as the site of the second alkylation with DMAPP catalyzed by the prenyltransferase asqH2 to yield a carbenium ion intermediate, which can be attacked by H(2)O to yield a styrenyl quinolone containing a C3'-hydroxyprenyl chain. The FAD-dependent monooxygenase asqG performs epoxidation of the terminal C7'-C8' olefin. Finally, after dehydratation of the epoxide at C3 by asqC, the quinolone epoxide rearrangement protein asqO catalyzes an enzymatic 3-exo-tet cyclization to yield the cyclopropyl-THF ring system in aspoquinolone (Probable).