title: Thermodynamics of the ligandin function of human class Alpha glutathione transferase A1-1: energetics of organic anion ligand binding.
abstract: In addition to their catalytic functions, cytosolic glutathioneS-transferases (GSTs) are a major reserve of high-capacity binding proteins for a large variety of physiological and exogenous non-substrate compounds. This ligandin function has implicated GSTs in numerous ligand-uptake, -transport and -storage processes. The binding of non-substrate ligands to GSTs can inhibit catalysis. In the present study, the energetics of the binding of the non-substrate ligand 8-anilino-1-naphthalene sulphonate (ANS) to wild-type human class Alpha GST with two type-1 subunits (hGSTA1-1) and its DeltaPhe-222 deletion mutant were studied by isothermal titration calorimetry. The stoichiometry of binding to both proteins is one ANS molecule per GST subunit with a greater affinity for the wild-type (K(d)=65 microM) than for the DeltaPhe-222 mutant (K(d)=105 microM). ANS binding to the wild-type protein is enthalpically driven and it is characterized by a large negative heat-capacity change, DeltaC(p). The negative DeltaC(p) value for ANS binding indicates a specific interface with a significant hydrophobic component in the protein-ligand complex. The negatively charged sulphonate group of the anionic ligand is apparently not a major determinant of its binding. Phe-222 contributes to the binding affinity for ANS and the hydrophobicity of the binding site.
authors.affiliation: Protein Structure-Function Research Programme, School of Molecular and Cell Biology, University of the Witwatersrand, Johannesburg 2050, South Africa.
authors.forename: Yasien
authors.initials: Y
authors.lastname: Sayed
authors.forename: Judith A T
authors.initials: JA
authors.lastname: Hornby
authors.forename: Marimar
authors.initials: M
authors.lastname: Lopez
authors.forename: Heini
authors.initials: H
authors.lastname: Dirr
mesh_terms: D000817:Anilino Naphthalenesulfonates; D000838:Anions; D001665:Binding Sites; D002151:Calorimetry; D004734:Energy Metabolism; D005982:Glutathione Transferase / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D066298:In Vitro Techniques; D007527:Isoenzymes / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D008024:Ligands; D010649:Phenylalanine / Q000737:chemistry; D021122:Protein Subunits; D011994:Recombinant Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D017384:Sequence Deletion; D013816:Thermodynamics
chemical_list: D000817:Anilino Naphthalenesulfonates; D000838:Anions; D007527:Isoenzymes; D008024:Ligands; D021122:Protein Subunits; D011994:Recombinant Proteins; D010649:Phenylalanine; C027132:1-anilino-8-naphthalenesulfonate; D005982:Glutathione Transferase; C119995:glutathione S-transferase alpha