On the reaction mechanism of class Pi glutathione S-transferase

• Published in: Proteins, structure, function, and bioinformatics Vol. 28; no. 4; pp. 530 - 542
• Main Authors: Orozco, Modesto, Vega, Cristina, Parraga, Antonio, García-Sáez, Isabel, Coll, Miquel, Walsh, Sinead, Mantle, Timothy J., Luque, F. Javier
• Format: Journal Article
• Language: English
• Published: Hoboken Wiley Subscription Services, Inc., A Wiley Company 01.08.1997
• Subjects: Animals; Computer Simulation; Dinitrochlorobenzene - chemistry; Dinitrochlorobenzene - metabolism; enzyme mechanism; free energy perturbation; Glutathione - chemistry; Glutathione - metabolism; glutathione S-transferase; Glutathione S-Transferase pi; Glutathione Transferase - chemistry; GST class Pi; Isoenzymes - chemistry; Mice; Models, Molecular; molecular dynamics; Protein Conformation; Thermodynamics; X-ray diffraction
• ISSN: 0887-3585; 1097-0134
• DOI: 10.1002/(SICI)1097-0134(199708)28:4<530::AID-PROT7>3.0.CO;2-D

Theoretical calculations were performed to examine the ionization of the phenolic group of Tyr7 and the thiol group of glutathione in aqueous solution and in the protein class‐pi glutathione S‐transferase (GST‐Pi). Three model systems were considered for simulations in the protein environment: the free enzyme, the complex between glutathione and the enzyme, and the complex between 1‐chloro‐2.4‐dinitrobenzene, glutathione, 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 GST‐Pi, the glutathione‐bound form of GST‐Pi, and the free enzyme carboxymethylated in Cys47. Free‐energy perturbation techniques were used to determine the thermodynamics quantities for ionization of the phenol and thiol groups. The functional implications of Tyr7 in the activation of the glutathione thiol group are discussed in the light of present 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 with Tyr7 and by interactions with hydrating water molecules. Proteins 28:530–542, 1997 © 1997 Wiley‐Liss, Inc.