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Human ?-amino-?-carboxymuconate-?-semialdehyde decarboxylase (ACMSD): a structural and mechanistic unveiling.

ABSTRACT: Human ?-amino-?-carboxymuconate-?-semialdehyde decarboxylase determines the fate of tryptophan metabolites in the kynurenine pathway by controlling the quinolinate levels for de novo nicotinamide adenine dinucleotide biosynthesis. The unstable nature of its substrate has made gaining insight into its reaction mechanism difficult. Our electron paramagnetic resonance (EPR) spectroscopic study on the Cu-substituted human enzyme suggests that the native substrate does not directly ligate to the metal ion. Substrate binding did not result in a change of either the hyperfine structure or the super-hyperfine structure of the EPR spectrum. We also determined the crystal structure of the human enzyme in its native catalytically active state (at 1.99 Å resolution), a substrate analogue-bound form (2.50 Å resolution), and a selected active site mutant form with one of the putative substrate binding residues altered (2.32 Å resolution). These structures illustrate that each asymmetric unit contains three pairs of dimers. Consistent with the EPR findings, the ligand-bound complex structure shows that the substrate analogue does not directly coordinate to the metal ion but is bound to the active site by two arginine residues through noncovalent interactions.

SUBMITTER: Huo L

PROVIDER: S-EPMC4289673 | biostudies-literature | 2015 Jan

REPOSITORIES: biostudies-literature

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Human α-amino-β-carboxymuconate-ε-semialdehyde decarboxylase (ACMSD): a structural and mechanistic unveiling.

Huo Lu L Liu Fange F Iwaki Hiroaki H Li Tingfeng T Hasegawa Yoshie Y Liu Aimin A

Proteins 20141121 1

Human α-amino-β-carboxymuconate-ε-semialdehyde decarboxylase determines the fate of tryptophan metabolites in the kynurenine pathway by controlling the quinolinate levels for de novo nicotinamide adenine dinucleotide biosynthesis. The unstable nature of its substrate has made gaining insight into its reaction mechanism difficult. Our electron paramagnetic resonance (EPR) spectroscopic study on the Cu-substituted human enzyme suggests that the native substrate does not directly ligate to the meta ...[more]

PMID: 25392945

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Project description:The 2-nitrobenzoic acid degradation pathway of Pseudomonas fluorescens strain KU-7 proceeds via a novel 3-hydroxyanthranilate intermediate. In this study, we cloned and sequenced a 19-kb DNA locus of strain KU-7 that encompasses the 3-hydroxyanthranilate meta-cleavage pathway genes. The gene cluster, designated nbaEXHJIGFCDR, is organized tightly and in the same direction. The nbaC and nbaD gene products were found to be novel homologs of the eukaryotic 3-hydroxyanthranilate 3,4-dioxygenase and 2-amino-3-carboxymuconate-6-semialdehyde decarboxylase, respectively. The NbaC enzyme carries out the oxidation of 3-hydroxyanthranilate to 2-amino-3-carboxymuconate-6-semialdehyde, while the NbaD enzyme catalyzes the decarboxylation of the latter compound to 2-aminomuconate-6-semialdehyde. The NbaC and NbaD proteins were overexpressed in Escherichia coli and characterized. The substrate specificity of the 23.8-kDa NbaC protein was found to be restricted to 3-hydroxyanthranilate. In E. coli, this enzyme oxidizes 3-hydroxyanthranilate with a specific activity of 8 U/mg of protein. Site-directed mutagenesis experiments revealed the essential role of two conserved histidine residues (His52 and His96) in the NbaC sequence. The NbaC activity is also dependent on the presence of Fe(2+) but is inhibited by other metal ions, such as Zn(2+), Cu(2+), and Cd(2+). The NbaD protein was overproduced as a 38.7-kDa protein, and its specific activity towards 2-amino-3-carboxymuconate-6-semialdehyde was 195 U/mg of protein. Further processing of 2-aminomuconate-6-semialdehyde to pyruvic acid and acetyl coenzyme A was predicted to proceed via the activities of NbaE, NbaF, NbaG, NbaH, NbaI, and NbaJ. The predicted amino acid sequences of these proteins are highly homologous to those of the corresponding proteins involved in the metabolism of 2-aminophenol (e.g., AmnCDEFGH in Pseudomonas sp. strain AP-3). The NbaR-encoding gene is predicted to have a regulatory function of the LysR family type. The function of the product of the small open reading frame, NbaX, like the homologous sequences in the nitrobenzene or 2-aminophenol metabolic pathway, remains elusive.

Dataset Information

Human ?-amino-?-carboxymuconate-?-semialdehyde decarboxylase (ACMSD): a structural and mechanistic unveiling.

Publications

Human α-amino-β-carboxymuconate-ε-semialdehyde decarboxylase (ACMSD): a structural and mechanistic unveiling.

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