ON THE REACTION-MECHANISM OF CLASS-PI GLUTATHIONE-S-TRANSFERASE

Theoretical calculations were performed to examine the ionization of t he phenolic group of Tyr7 and the thiol group of glutathione Sn aqueou s solution and in the protein class-pi glutathione S-transferase (GST- Pi), Three model systems were considered for simulations in the protei n environment: the free enzyme, the complex between glutathione: and t he enzyme, and the complex between 1-chloro-2.4-dinitrobenzene, glutat hione, and the enzyme, The structures derived from Molecular Dynamics simulations were compared with the crystallographic data available for the complex between the inhibitor S-(p-nitrobenzyl)glutathione and GS T-Pi, the glutathione-bound form of GST-Pi, and the free enzyme carbox ymethylated in Cys47. Free-energy per turbation techniques were used t o determine the thermodynamics quantities for ionization of the phenol and thiol groups, The functional implications of Tyr7 in the activati on of the glutathione thiol group are discussed in the light of presen t results, which in agreement with previous studies suggest that Tyr7 in un-ionized form contributes to the catalytic process of glutathione S-transferase, the thiolate anion being stabilized by hydrogen bond w ith Tyr7 and by interactions with hydrating water molecules. (C) 1997 Wiley-Liss, Inc.