3-DIMENSIONAL STRUCTURE OF THE GLUTATHIONE SYNTHETASE FROM ESCHERICHIA-COLI-B AT 2.O-ANGSTROM RESOLUTION

Glutathione synthetase (γ-L-glutamyl-L-cysteine: glycine ligase (ADP-forming) EC 6.3.2.3: GSHase) catalyzes the synthesis of glutathione from γ-L-glutamyl-L-cysteine and Gly in the presence of ATP. The enzyme from Escherichia coli is a tetramer with four identical subunits of 316 amino acid residues. The crystal structure of the enzyme has been determined by isomorphous replacement and refined to a 2.0 Å resolution. Two regions, Gly 164 to Gly 167 and Ile226 to Arg241, are invisible on the electron density map. The refined model of the subunit includes 296 amino acid residues and 107 solvent molecules. The crystallographic R-factor is 18.6% for 17,914 reflections with F > 3σ between 6.0 Å and 2.0 Å. The structure consists of three domains: the N-terminal, central, and C-terminal domains. In the tetrameric molecule, two subunits that are in close contact form a tight dimer, two tight dimers forming a tetramer with two solvent regions. The ATP molecule is located in the cleft between the central and C-terminal domains. The ATP binding site is surrounded by two sets of the structural motif that belong to those respective domains. Each motif consists of an anti-parallel β-sheet and a glycine-rich loop.