Native dimer stabilizes the subunit tertiary structure of porcine class pi glutathione S-transferase.

Solvent-induced unfolding of porcine class pi glutathione S-transferase (pGST P1-1), a homodimeric protein, was monitored under equilibrium conditions using different physicochemical parameters (tryptophan fluorescence, anisotropy, degree of tyrosine exposure, binding of 8-anilino-1-naphthalenesulphonic acid, size-exclusion HPLC). The coincidence of unfolding curves obtained with functional (enzyme activity) and structural probes (anisotropy), the absence of thermodynamically stable intermediates such as a folded monomer (determined by binding of 8-anilino-1-naphthalenesulphonic acid and size-exclusion HPLC), and the dependence of pGST P1-1 stability upon protein concentration (measured with structural and functional probes), indicate a cooperative and concerted two-state unfolding transition between native dimeric pGST P1-1 and unfolded monomeric enzyme.