Human α-amino-β-carboxymuconate-ε-semialdehyde decarboxylase (ACMSD): a structural and mechanistic unveiling.
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 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.
Department of Chemistry and the Center for Diagnostics and Therapeutics, Georgia State University, Atlanta, Georgia 30303.
Lu
L
Huo
Fange
F
Liu
Hiroaki
H
Iwaki
Tingfeng
T
Li
Yoshie
Y
Hasegawa
Aimin
A
Liu
D055162:Biocatalysis; D002262:Carboxy-Lyases / Q000737:chemistry* / Q000378:metabolism*; D020134:Catalytic Domain; D018360:Crystallography, X-Ray; D004578:Electron Spin Resonance Spectroscopy; D004926:Escherichia coli / Q000378:metabolism; D006801:Humans; D008958:Models, Molecular; D055503:Protein Multimerization; D013379:Substrate Specificity; D013696:Temperature; D015032:Zinc / Q000378:metabolism
D002262:Carboxy-Lyases; C024396:aminocarboxymuconate-semialdehyde decarboxylase; D015032:Zinc
Tryptophan metabolites; kynurenine; quaternary structure; quinolinate synthesis