title: Crystal structures and kinetic studies of human Kappa class glutathione transferase provide insights into the catalytic mechanism.
abstract: GSTs (glutathione transferases) are a family of enzymes that primarily catalyse nucleophilic addition of the thiol of GSH (reduced glutathione) to a variety of hydrophobic electrophiles in the cellular detoxification of cytotoxic and genotoxic compounds. GSTks (Kappa class GSTs) are a distinct class because of their unique cellular localization, function and structure. In the present paper we report the crystal structures of hGSTk (human GSTk) in apo-form and in complex with GTX (S-hexylglutathione) and steady-state kinetic studies, revealing insights into the catalytic mechanism of hGSTk and other GSTks. Substrate binding induces a conformational change of the active site from an 'open' conformation in the apo-form to a 'closed' conformation in the GTX-bound complex, facilitating formations of the G site (GSH-binding site) and the H site (hydrophobic substrate-binding site). The conserved Ser(16) at the G site functions as the catalytic residue in the deprotonation of the thiol group and the conserved Asp(69), Ser(200), Asp(201) and Arg(202) form a network of interactions with γ-glutamyl carboxylate to stabilize the thiolate anion. The H site is a large hydrophobic pocket with conformational flexibility to allow the binding of different hydrophobic substrates. The kinetic mechanism of hGSTk conforms to a rapid equilibrium random sequential Bi Bi model.
authors: State Key Laboratory of Molecular Biology and Research Center for Structural Biology, Institute of Biochemistry and Cell Biology, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, Shanghai 200031, China.
authors: Bing
authors: B
authors: Wang
authors: Yingjie
authors: Y
authors: Peng
authors: Tianlong
authors: T
authors: Zhang
authors: Jianping
authors: J
authors: Ding
mesh_terms: D000595:Amino Acid Sequence; D055162:Biocatalysis; D018360:Crystallography, X-Ray; D005982:Glutathione Transferase / Q000737:chemistry* / Q000378:metabolism*; D006801:Humans; D007700:Kinetics; D008958:Models, Molecular; D008969:Molecular Sequence Data; D011487:Protein Conformation; D017386:Sequence Homology, Amino Acid; D013329:Structure-Activity Relationship
chemical_list: D005982:Glutathione Transferase