title: Crystal structure of Glycine max glutathione transferase in complex with glutathione: investigation of the mechanism operating by the Tau class glutathione transferases.
abstract: Cytosolic GSTs (glutathione transferases) are a multifunctional group of enzymes widely distributed in Nature and involved in cellular detoxification processes. The three-dimensional structure of GmGSTU4-4 (Glycine max GST Tau 4-4) complexed with GSH was determined by the molecular replacement method at 2.7 A (1 A=0.1 nm) resolution. The bound GSH is located in a region formed by the beginning of alpha-helices H1, H2 and H3 in the N-terminal domain of the enzyme. Significant differences in the G-site (GSH-binding site) as compared with the structure determined in complex with Nb-GSH [S-(p-nitrobenzyl)-glutathione] were found. These differences were identified in the hydrogen-bonding and electrostatic interaction pattern and, consequently, GSH was found bound in two different conformations. In one subunit, the enzyme forms a complex with the ionized form of GSH, whereas in the other subunit it can form a complex with the non-ionized form. However, only the ionized form of GSH may form a productive and catalytically competent complex. Furthermore, a comparison of the GSH-bound structure with the Nb-GSH-bound structure shows a significant movement of the upper part of alpha-helix H4 and the C-terminal. This indicates an intrasubunit modulation between the G-site and the H-site (electrophile-binding site), suggesting that the enzyme recognizes the xenobiotic substrates by an induced-fit mechanism. The reorganization of Arg111 and Tyr107 upon xenobiotic substrate binding appears to govern the intrasubunit structural communication between the G- and H-site and the binding of GSH. The structural observations were further verified by steady-state kinetic analysis and site-directed mutagenesis studies.
authors.affiliation: Laboratory of Enzyme Technology, Department of Agricultural Biotechnology, Agricultural University of Athens, 75 Iera Odos Street, GR-11855-Athens, Greece.
authors.forename: Irene
authors.initials: I
authors.lastname: Axarli
authors.forename: Prathusha
authors.initials: P
authors.lastname: Dhavala
authors.forename: Anastassios C
authors.initials: AC
authors.lastname: Papageorgiou
authors.forename: Nikolaos E
authors.initials: NE
authors.lastname: Labrou
mesh_terms: D003460:Crystallization; D018360:Crystallography, X-Ray; D005978:Glutathione / Q000737:chemistry* / Q000378:metabolism; D005982:Glutathione Transferase / Q000737:chemistry* / Q000145:classification / Q000235:genetics; D016297:Mutagenesis, Site-Directed; D010940:Plant Proteins / Q000737:chemistry* / Q000145:classification / Q000235:genetics; D017433:Protein Structure, Secondary / Q000235:genetics; D017434:Protein Structure, Tertiary / Q000235:genetics; D013025:Glycine max / Q000737:chemistry* / Q000235:genetics; D016875:tau Proteins / Q000737:chemistry* / Q000145:classification
chemical_list: D010940:Plant Proteins; D016875:tau Proteins; D005982:Glutathione Transferase; D005978:Glutathione