Structural analysis of human alpha-class glutathione transferase A1-1 in the apo-form and in complexes with ethacrynic acid and its glutathione conjugate

• DOI: 10.1016/s0969-2126(01)00206-4
• Publication Date: 2004-07-23T19:10:35Z
• Authors: Alexander D Cameron; Irmgard Sinning; Guillaume L'Hermite; Birgit Olin; Philip G Board; Bengt Mannervik; T.Alwyn Jones
• Keywords: Tripeptide; Conjugate; Glutathione S-transferase

Glutathione transferases (GSTs) constitute a family of isoenzymes that catalyze the conjugation of the tripeptide glutathione with a wide variety of hydrophobic compounds bearing an electrophilic functional group. Recently, a number of X-ray structures have been reported which have defined both the glutathione- and the substrate-binding sites in these enzymes. The structure of the glutathione-free enzyme from a mammalian source has not, however, been reported previously.We have solved structures of a human alpha-class GST, isoenzyme A1-1, both in the unliganded form and in complexes with the inhibitor ethacrynic acid and its glutathione conjugate. These structures have been refined to resolutions of 2.5 A, 2.7 A and 2.0 A respectively. Both forms of the inhibitor are clearly present in the associated electron density.The major differences among the three structures reported here involve the C-terminal alpha-helix, which is a characteristic of the alpha-class enzyme. This helix forms a lid over the active site when the hydrophobic substrate binding site (H-site) is occupied but it is otherwise disordered. Ethacrynic acid appears to bind in a non-productive mode in the absence of the coenzyme glutathione.