title: Reactions catalyzed by 5-aminoimidazole ribonucleotide carboxylases from Escherichia coli and Gallus gallus: a case for divergent catalytic mechanisms.
abstract: A comparative investigation of the substrate requirements for the enzyme 5-aminoimidazole ribonucleotide (AIR) carboxylase from E. coli and G. gallus has been conducted using in vivo and in vitro studies. In Escherichia coli, two enzymes PurK and PurE are required for the transformation of AIR to 4-carboxy-5-aminoimidazole ribonucleotide (CAIR). The Gallus gallus PurCE is a bifunctional enzyme containing AIR carboxylase and 4-[(N-succinylamino)carbonyl]-5-aminoimidazole ribonucleotide (SAICAR) synthetase. The E. coli PurE and the C-terminal domain of the G. gallus PurCE protein maintain a significant degree of amino acid sequence identity and also share CAIR as a product of their enzymatic activities. The substrate requirements of AIR carboxylases from E. coli and G. gallus have been compared by a series of in vitro experiments. The carbamic acid, N5-carboxyaminoimidazole ribonucleotide (N5-CAIR) is a substrate for the E. coli PurE (Mueller et al., 1994) but not for the G. gallus AIR carboxylase. In contrast, AIR and CO2 are substrates for the G. gallus AIR carboxylase. The recognition properties of the two proteins were also compared using inhibition studies with 4-nitro-5- aminoimidazole ribonucleotide (NAIR). NAIR is a tight-binding inhibitor of the G. gallus AIR carboxylase (K(i) = 0.34 nM) but only a steady-state inhibitor (K(i) = 0.5 microM) of the E. coli PurE. These data suggest significant differences in the transition states for the reactions catalyzed by these two evolutionarily related enzymes.(ABSTRACT TRUNCATED AT 250 WORDS)
authors.affiliation: Department of Medicinal Chemistry and Pharmacognosy, Purdue University, West Lafayette, Indiana 47907-1333.
authors.forename: S M
authors.initials: SM
authors.lastname: Firestine
authors.forename: S W
authors.initials: SW
authors.lastname: Poon
authors.forename: E J
authors.initials: EJ
authors.lastname: Mueller
authors.forename: J
authors.initials: J
authors.lastname: Stubbe
authors.forename: V J
authors.initials: VJ
authors.lastname: Davisson
mesh_terms: D000620:Aminoimidazole Carboxamide / Q000031:analogs & derivatives / Q000378:metabolism; D000818:Animals; D001483:Base Sequence; D005075:Biological Evolution; D002245:Carbon Dioxide / Q000378:metabolism; D002262:Carboxy-Lyases / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D002384:Catalysis; D002645:Chickens / Q000235:genetics / Q000378:metabolism*; D004926:Escherichia coli / Q000201:enzymology* / Q000235:genetics / Q000254:growth & development; D005816:Genetic Complementation Test; D009682:Magnetic Resonance Spectroscopy; D008969:Molecular Sequence Data; D009593:Nitroimidazoles / Q000494:pharmacology; D010453:Peptide Synthases / Q000235:genetics / Q000378:metabolism*; D012265:Ribonucleotides / Q000378:metabolism / Q000494:pharmacology; D013379:Substrate Specificity; D014170:Transformation, Genetic
chemical_list: C084132:5-amino-1-(5'-phosphoribofuranosyl)-4-nitroimidazole; D009593:Nitroimidazoles; D012265:Ribonucleotides; D002245:Carbon Dioxide; C024828:aminoimidazole ribotide; D000620:Aminoimidazole Carboxamide; D002262:Carboxy-Lyases; C022378:phosphoribosylaminoimidazole carboxylase; D010453:Peptide Synthases; C022379:phosphoribosylaminoimidazole-succinocarboxamide synthetase; C031143:AICA ribonucleotide; C020635:SAICAR