title: Bacterial 2,4-dioxygenases: new members of the alpha/beta hydrolase-fold superfamily of enzymes functionally related to serine hydrolases.
abstract: 1H-3-hydroxy-4-oxoquinoline 2,4-dioxygenase (Qdo) from Pseudomonas putida 33/1 and 1H-3-hydroxy-4-oxoquinaldine 2,4-dioxygenase (Hod) from Arthrobacter ilicis Rü61a catalyze an N-heterocyclic-ring cleavage reaction, generating N-formylanthranilate and N-acetylanthranilate, respectively, and carbon monoxide. Amino acid sequence comparisons between Qdo, Hod, and a number of proteins belonging to the alpha/beta hydrolase-fold superfamily of enzymes and analysis of the similarity between the predicted secondary structures of the 2,4-dioxygenases and the known secondary structure of haloalkane dehalogenase from Xanthobacter autotrophicus GJ10 strongly suggested that Qdo and Hod are structurally related to the alpha/beta hydrolase-fold enzymes. The residues S95 and H244 of Qdo were found to be arranged like the catalytic nucleophilic residue and the catalytic histidine, respectively, of the alpha/beta hydrolase-fold enzymes. Investigation of the potential functional significance of these and other residues of Qdo through site-directed mutagenesis supported the hypothesis that Qdo is structurally as well as functionally related to serine hydrolases, with S95 being a possible catalytic nucleophile and H244 being a possible catalytic base. A hypothetical reaction mechanism for Qdo-catalyzed 2,4-dioxygenolysis, involving formation of an ester bond between the catalytic serine residue and the carbonyl carbon of the substrate and subsequent dioxygenolysis of the covalently bound anionic intermediate, is discussed.
authors.affiliation: Mikrobiologie, Fachbereich 7, Carl von Ossietzky Universität Oldenburg, Oldenburg, Germany.
authors.forename: F
authors.initials: F
authors.lastname: Fischer
authors.forename: S
authors.initials: S
authors.lastname: Künne
authors.forename: S
authors.initials: S
authors.lastname: Fetzner
mesh_terms: D000595:Amino Acid Sequence; D001173:Arthrobacter / Q000201:enzymology; D001419:Bacteria / Q000201:enzymology*; D049308:Dioxygenases; D007700:Kinetics; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D010105:Oxygenases / Q000737:chemistry* / Q000378:metabolism; D017510:Protein Folding; D017433:Protein Structure, Secondary; D016958:Pseudomonas putida / Q000201:enzymology; D011994:Recombinant Proteins / Q000737:chemistry / Q000378:metabolism; D016415:Sequence Alignment; D017386:Sequence Homology, Amino Acid
chemical_list: D011994:Recombinant Proteins; D010105:Oxygenases; C101932:1H-3-hydroxy-4-oxoquinaldine 2,4-dioxygenase (decyclizing, CO-forming); D049308:Dioxygenases