西亚试剂：Crystal structures and kinetic studies of human kappa class

Crystal structures and kinetic studies of human kappa class glutathione transferase provide insights into the catalytic mechanism

Bing Wang, Yingjie Peng, Tianlong Zhang and Jianping Ding

Glutathione transferases (GSTs) are a family of enzymes that primarily catalyze nucleophilic addition of the thiol of glutathione (GSH) to a variety of hydrophobic electrophiles in the cellular detoxification of cytotoxic and genotoxic compounds. Kappa class GSTs (GSTks) are a distinct class for their unique cellular localization, function, and structure. We report here the crystal structures of human GSTk (hGSTk) in apo form and in complex with S-hexylglutathione (GTX) and the steady-state kinetic studies, revealing insights into the catalytic mechanism of hGSTk and other GSTks. The substrate binding induces 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 GSH-binding site (G site) and the hydrophobic substrate-binding site (H site). The conserved Ser16 at the G site functions as the catalytic residue in the deprotonation of the thiol group and the conserved Asp69, Ser200, Asp201, and Arg202 form a network of interactions with the g-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.