FEATURES

FAMILY

DESCRIPTION

Also known as ASQJ_EMENI, asqJ. Iron/alpha-ketoglutarate-dependent dioxygenase; part of the gene cluster that mediates the biosynthesis of the aspoquinolone mycotoxins (PubMed:25251934, PubMed:26553478). The first stage is catalyzed by the nonribosomal pepdide synthetase asqK that condenses anthranilic acid and O-methyl-L-tyrosine to produce 4'-methoxycyclopeptin (PubMed:25251934). AsqK is also able to use anthranilic acid and L-phenylalanine as substrates to produce cyclopeptin, but at a tenfold lower rate (PubMed:25251934). 4'-methoxycyclopeptin is then converted to 4'-methoxydehydrocyclopeptin by the ketoglutarate-dependent dioxygenase asqJ through dehydrogenation to form a double bond between C-alpha and C-beta of the O-methyltyrosine side chain (PubMed:25251934, PubMed:26553478). AsqJ also converts its first product 4'-methoxydehydrocyclopeptin to 4'-methoxycyclopenin (PubMed:25251934). AsqJ is a very unique dioxygenase which is capable of catalyzing radical-mediated dehydrogenation and epoxidation reactions sequentially on a 6, 7-benzo-diazepinedione substrate in the 4'-methoxyviridicatin biosynthetic pathway (PubMed:25251934). AsqJ is also capable of converting cyclopeptin into dehydrocyclopeptin (PubMed:25251934). The following conversion of 4'-methoxycyclopenin into 4'-methoxyviridicatin is catalyzed by the cyclopenase asqI (PubMed:30026518). Cyclopenin can also be converted into viridicatin by asqI (PubMed:30026518). 4'-methoxyviridicatin is the precursor of quinolone natural products, and is further converted to quinolinone B (Probable). 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 (By similarity). 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 (By similarity). The FAD-dependent monooxygenase asqG performs epoxidation of the terminal C7'-C8' olefin (PubMed:30026518). 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 (PubMed:30026518). Homodimer.

EXTERNAL LINKS

asqJ

Iron/alpha-ketoglutarate-dependent dioxygenase asqJ

asqJ

Molecular Synopsis