2imd
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Structure of SeMet 2-hydroxychromene-2-carboxylate isomerase (HCCA isomerase)
OverviewOverview
The enzyme 2-hydroxychromene-2-carboxylic acid (HCCA) isomerase catalyzes, the glutathione (GSH)-dependent interconversion (Keq = 1.5) of HCCA and, trans-o-hydroxybenzylidene pyruvic acid (tHBPA) in the naphthalene, catabolic pathway of Pseudomonas putida. The dimeric protein binds one, molecule of GSH very tightly (Kd approximately 5 nM) and a second molecule, of GSH with much lower affinity (Kd approximately 2 to 11 muM). The enzyme, is unstable in the absence of GSH. The turnover number in the forward, direction (47 s-1 at 25 degrees C) greatly exceeds off rates for GSH (koff, approximately 10-3 to 10-2 s-1 at 10 degrees C), suggesting that GSH acts, as a tightly bound cofactor in the reaction. The crystal structure of the, enzyme at 1.7 A resolution reveals that the isomerase is closely related, to class kappa GSH transferases. Diffraction quality crystals could only, be obtained in the presence of GSH and HCCA/tHBPA. Clear electron density, is seen for GSH. Electron density for the organic substrates is located, near the GSH and is best modeled to include both HCCA and tHBPA at, occupancies of 0.5 for each. Although there is no electron density, connecting the sulfur of GSH to the organic substrates, the sulfur is, located very close (2.78 A) to C7 of HCCA. Taken together, the results, suggest that the isomerization reaction involves a short-lived covalent, adduct between the sulfur of GSH and C7 of the substrate.
About this StructureAbout this Structure
2IMD is a Single protein structure of sequence from Pseudomonas putida with , , , and as ligands. Active as Glutathione transferase, with EC number 2.5.1.18 Full crystallographic information is available from OCA.
ReferenceReference
2-Hydroxychromene-2-carboxylic Acid Isomerase: A Kappa Class Glutathione Transferase from Pseudomonas putida(,)(,)., Thompson LC, Ladner JE, Codreanu SG, Harp J, Gilliland GL, Armstrong RN, Biochemistry. 2007 Jun 12;46(23):6710-6722. Epub 2007 May 18. PMID:17508726
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