6月28日，《生化期刊》（Biochemical Journal）在线发表了中科院上海生命科学研究院生物化学与细胞生物学研究所丁建平研究组关于人源kappa类谷胱甘肽转移酶（hGSTk）催化机制的最新研究成果。
谷胱甘肽转移酶（GST）是生物体内一类重要的解毒酶，主要催化将体内疏水毒性分子亲核加成到还原性谷胱甘肽（GSH）的反应，广泛存在于各类原核和真核生物中。Kappa类GST由于其独特的细胞定位、氨基酸序列和拓扑结构，被特别单独分类，以区别于被广泛研究的胞浆/可溶性/经典类GST。在以往的研究中，这类GSTk的催化机制还未得到清楚的阐述。
丁建平研究组博士生王冰等人解析了不结合底物与结合抑制剂S-hexylglutathione（GTX）的两种不同形式的hGSTk晶体结构，结合稳态酶动力学研究，揭示了hGSTk的催化机制。不同形式的hGSTk结构显示，在结合底物前后，hGSTk由“敞开”式构象变为“闭合”式构象，以形成完整的GSH结合位点（G位点）和疏水底物结合位点（H位点）。G位点保守的Ser16残基作为催化残基在反应中夺取GSH巯基的质子，而保守的Asp69、Ser200、Asp201和Arg202与GSH的g-谷氨酰羧基形成相互作用网络，稳定了GS-的电荷。hGSTk的H位点位于蛋白表面的大型疏水口袋，这个疏水口袋的构象具有高度灵活性，可以适应各种不同疏水底物的结合。酶动力学研究还表明，hGSTk在催化GSH和底物CDNB的连接反应中采取了快速平衡随机顺序双-双模型。研究结果还提示，其它GSTk酶可能采用同样的催化反应机制。
这一研究成果将有助于人们进一步理解不同类型的谷胱甘肽转移酶之间的进化关系，以及它们在体内的不同生物学功能。（生物谷Bioon.com）
生物谷推荐原文出处：
Biochemical Journal doi:10.1042/BJ20110753
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.
