Crystal structure of γ-glutamylcysteine synthetase: Insights into the mechanism of catalysis by a key enzyme for glutathione homeostasis

• DOI: 10.1073/pnas.0403277101
• Publication Date: 2004-10-12T00:24:32Z
• Authors: Takao Hibi; Hiroshi Nii; Toru Nakatsu; Akira Kimura; Hiroaki Kato; Jun Hiratake; Jun'ichi Oda
• Keywords: Inhibitor protein; Transition state analog

γ-Glutamylcysteine synthetase (γGCS), a rate-limiting enzyme in glutathione biosynthesis, plays central role homeostasis and is target for development of potential therapeutic agents against parasites cancer. We have determined the crystal structures Escherichia coli γGCS unliganded complexed with sulfoximine-based transition-state analog inhibitor at resolutions 2.5 2.1 Å, respectively. In structure complex, bound phosphorylated sulfoximido nitrogen coordinated to three Mg 2+ ions. The cysteine-binding site was identified; it formed inductively transition state. structure, an open space exists around representative probably responsible competitive binding glutathione. Upon binding, side chains Tyr-241 Tyr-300 turn, forming hydrogen-bonding triad carboxyl group inhibitor's cysteine moiety, allowing this moiety fit tightly into concomitant accommodation its chain shallow pocket. This movement caused by conformational change switch loop (residues 240–249). Based on sites mammalian parasitic γGCSs were predicted multiple sequence alignment, although no significant identity between E. eukaryotic homologues. identification provides important information rational design novel inhibitors.