Three-dimensional structure of glutathione S-transferase from Arabidopsis thaliana at 2.2 angstrom resolution: Structural characterization of herbicide-conjugating plant glutathione S-transferases and a novel active site architecture

• Published in: Journal of molecular biology 1996-01, Vol.255 (2), p.289-309
• Main Authors: Reinemer, P, Prade, L, Hof, P, Neuefeind, T, Huber, R, Zettl, R, Palme, K, Schell, J, Koelln, I
• Format: Article
• Language: English
• Subjects: Arabidopsis thaliana
• ISSN: 0022-2836
• DOI: 10.1006/jmbi.1996.0024

Glutathione S-transferases (GST) are a family of multifunctional enzymes involved in the metabolization of a broad variety of xenobiotics and reactive endogenous compounds. The interest in plant glutathione S-transferases may be attributed to their agronomic value, since it has been demonstrated that glutathione conjugation for a variety of herbicides is the major resistance and selectivity factor in plants. The three-dimensional structure of glutathione S-transferase from the plant Arabidopsis thaliana has been solved by multiple isomorphous replacement and multiwavelength anomalous dispersion techniques at 3 angstrom resolution and refined to a final crystallographic R-factor of 17.5% using data from 8 to 2.2 angstrom resolution. The enzyme forms a dimer of two identical subunits each consisting of 211 residues. Each subunit is characterized by the GST-typical modular structure with two spatially distinct domains. Domain I consists of a central four-stranded beta -sheet flanked on one side by two alpha -helices and on the other side by an irregular segment containing three short 3 sub(10)-helices, while domain II is entirely helical. The dimeric molecule is globular with a prominent large cavity formed between the two subunits. The active site is located in a cleft situated between domains I and II and each subunit binds two molecules of a competitive inhibitor S-hexylglutathione. Both hexyl moieties are oriented parallel and fill the H-subsite of the enzyme's active site. The glutathione peptide of one inhibitor, termed productive binding, occupies the G-subsite with multiple interactions similar to those observed for other glutathione S-transferases, while the glutathione backbone of the second inhibitor, termed unproductive binding, exhibits only weak interactions mediated by two polar contacts. A most striking difference from the mammalian glutathione S-transferases, which share a conserved catalytic tyrosine residue, is the lack of this tyrosine in the active site of the plant glutathione S-transferase.