THE 3-DIMENSIONAL STRUCTURE OF A CLASS-PI GLUTATHIONE-S-TRANSFERASE COMPLEXED WITH GLUTATHIONE - THE ACTIVE-SITE HYDRATION PROVIDES INSIGHTS INTO THE REACTION-MECHANISM

The structure of mouse liver glutathione S-transferase P1-1 complexed with its substrate glutathione (GSH) has been determined by X-ray diff raction analysis. No conformational changes in the glutathione moiety or in the protein, other than small adjustments of some side chains, a re observed when compared with glutathione adduct complexes. Our struc ture confirms that the role of Tyr-7 is to stabilize the thiolate by h ydrogen bonding and to position it in the right orientation. A compari son of the enzyme-GSH structure reported here with previously describe d structures reveals rearrangements in a well-defined network of water molecules in the active site. One of these water molecules (WO), iden tified in the unliganded enzyme (carboxymethylated at Cys-47), is disp laced by the binding of GSH, and a further water molecule (W4) is disp laced following the binding of the electrophilic substrate and the for mation of the glutathione conjugate. The possibility that one of these water molecules participates in the proton abstraction from the gluta thione thiol is discussed.