Reinemer P, Prade L, Hof P, Neuefeind T, Huber R, Zettl R, Palme K, Schell J, Koelln I, Bartunik H D, Bieseler B
Bayer AG, GB Pflanzenschutz (PF-F Biotechnologie) Pflanzenschutzzentrum Monheim, Leverkusen, Germany.
J Mol Biol. 1996 Jan 19;255(2):289-309. 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 A resolution and refined to a final crystallographic R-factor of 17.5% using data from 8 to 2.2 A 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(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.
谷胱甘肽S-转移酶（GST）是一类多功能酶，参与多种外源性物质和内源性反应性化合物的代谢。对植物谷胱甘肽S-转移酶的关注可能归因于它们的农学价值，因为已经证明，植物对多种除草剂的谷胱甘肽结合作用是主要的抗性和选择性因素。通过多同晶置换和多波长反常色散技术，以3埃分辨率解析了来自拟南芥的谷胱甘肽S-转移酶的三维结构，并使用8至2.2埃分辨率的数据将其精修至最终晶体学R因子为17.5%。该酶由两个相同的亚基形成二聚体，每个亚基由211个残基组成。每个亚基具有谷胱甘肽S-转移酶典型的模块化结构，有两个空间上不同的结构域。结构域I由一个中央四链β-折叠组成，一侧由两个α-螺旋侧翼，另一侧由一个包含三个短3（10）-螺旋的不规则片段侧翼，而结构域II完全是螺旋结构。二聚体分子呈球状，在两个亚基之间形成一个突出的大腔。活性位点位于结构域I和II之间的裂隙中，每个亚基结合两个竞争性抑制剂S-己基谷胱甘肽分子。两个己基部分平行排列并填充酶活性位点的H亚位点。一种抑制剂的谷胱甘肽肽，称为有效结合，以与其他谷胱甘肽S-转移酶观察到的类似的多种相互作用占据G亚位点，而第二种抑制剂的谷胱甘肽主链，称为无效结合，仅通过两个极性接触表现出弱相互作用。与具有保守催化酪氨酸残基的哺乳动物谷胱甘肽S-转移酶最显著的区别是，植物谷胱甘肽S-转移酶的活性位点缺乏这种酪氨酸。
