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Dioxygenase AsqJ in complex with 2 and TrisDioxygenase AsqJ in complex with 2 and Tris
Structural highlights
FunctionASQJ_EMENI 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). The following conversion of 4'-methoxycyclopenin into 4'-methoxyviridicatin proceeds non-enzymatically (PubMed:25251934). AsqJ is also capable of converting cyclopeptin into dehydrocyclopeptin and cyclopenin in a sequential fashion (PubMed:25251934). Cyclopenin can be converted into viridicatin non-enzymatically (PubMed:25251934). 4'-methoxyviridicatin likely acts as a precursor of quinolone natural products, such as aspoquinolones, peniprequinolones, penigequinolones, and yaequinolones (PubMed:25251934). Further characterization of the remaining genes in the cluster has still to be done to determine the exact identity of quinolone products this cluster is responsible for biosynthesizing (PubMed:25251934).[1] [2] Publication Abstract from PubMedDioxygenases catalyze stereoselective oxygen atom transfer in metabolic pathways of biological, industrial, and pharmaceutical importance, but their precise chemical principles remain controversial. The alpha-ketoglutarate (alphaKG)-dependent dioxygenase AsqJ synthesizes biomedically active quinolone alkaloids via desaturation and subsequent epoxidation of a carbon-carbon bond in the cyclopeptin substrate. Here, we combine high-resolution X-ray crystallography with enzyme engineering, quantum-classical (QM/MM) simulations, and biochemical assays to describe a peroxidic intermediate that bridges the substrate and active site metal ion in AsqJ. Homolytic cleavage of this moiety during substrate epoxidation generates an activated high-valent ferryl (Fe(IV) = O) species that mediates the next catalytic cycle, possibly without the consumption of the metabolically valuable alphaKG cosubstrate. Our combined findings provide an important understanding of chemical bond activation principles in complex enzymatic reaction networks and molecular mechanisms of dioxygenases. Peroxy Intermediate Drives Carbon Bond Activation in the Dioxygenase AsqJ.,Auman D, Ecker F, Mader SL, Dorst KM, Brauer A, Widmalm G, Groll M, Kaila VRI J Am Chem Soc. 2022 Aug 18. doi: 10.1021/jacs.2c05650. PMID:35980821[3] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. See AlsoReferences
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