Porcine class pi glutathione S-transferase: anionic ligand binding and conformational analysis.

The equilibrium binding of the non-substrate ligands 8-anilino-1-naphthalene sulfonate and bromosulfophthalein to porcine class pi glutathione S-transferase (pGSTP1-1) was studied using a variety of techniques (size-exclusion HPLC, steady-state fluorescence, second-derivative spectroscopy, and chemical modification of cysteines). Both ligands share the same binding site which has a highly hydrophobic surface. Occupation of the site inhibits catalytic function with glutathione and 1-chloro-2,4-dinitrobenzene in a non-competitive manner. Data obtained from different structural probes either located at strategic regions of pGSTP1-1 (Trp-28, Trp-38 and Cys-45) or distributed throughout the protein molecule (tyrosine residues) suggest that binding induces a microstructural change that impacts on the functional conformation of the active site.