6月28日,，《生化期刊》（Biochemical Journal）在線發(fā)表了中科院上海生命科學(xué)研究院生物化學(xué)與細(xì)胞生物學(xué)研究所丁建平研究組關(guān)于人源kappa類谷胱甘肽轉(zhuǎn)移酶（hGSTk）催化機(jī)制的最新研究成果,。
谷胱甘肽轉(zhuǎn)移酶（GST）是生物體內(nèi)一類重要的解毒酶,，主要催化將體內(nèi)疏水毒性分子親核加成到還原性谷胱甘肽（GSH）的反應(yīng)，廣泛存在于各類原核和真核生物中,。Kappa類GST由于其獨(dú)特的細(xì)胞定位,、氨基酸序列和拓?fù)浣Y(jié)構(gòu)，被特別單獨(dú)分類,，以區(qū)別于被廣泛研究的胞漿/可溶性/經(jīng)典類GST,。在以往的研究中，這類GSTk的催化機(jī)制還未得到清楚的闡述,。
丁建平研究組博士生王冰等人解析了不結(jié)合底物與結(jié)合抑制劑S-hexylglutathione（GTX）的兩種不同形式的hGSTk晶體結(jié)構(gòu),，結(jié)合穩(wěn)態(tài)酶動(dòng)力學(xué)研究，揭示了hGSTk的催化機(jī)制,。不同形式的hGSTk結(jié)構(gòu)顯示,，在結(jié)合底物前后，hGSTk由“敞開”式構(gòu)象變?yōu)?ldquo;閉合”式構(gòu)象,，以形成完整的GSH結(jié)合位點(diǎn)（G位點(diǎn)）和疏水底物結(jié)合位點(diǎn)（H位點(diǎn)）,。G位點(diǎn)保守的Ser16殘基作為催化殘基在反應(yīng)中奪取GSH巰基的質(zhì)子，而保守的Asp69,、Ser200,、Asp201和Arg202與GSH的g-谷氨酰羧基形成相互作用網(wǎng)絡(luò)，穩(wěn)定了GS-的電荷,。hGSTk的H位點(diǎn)位于蛋白表面的大型疏水口袋,，這個(gè)疏水口袋的構(gòu)象具有高度靈活性，可以適應(yīng)各種不同疏水底物的結(jié)合,。酶動(dòng)力學(xué)研究還表明,，hGSTk在催化GSH和底物CDNB的連接反應(yīng)中采取了快速平衡隨機(jī)順序雙-雙模型。研究結(jié)果還提示,，其它GSTk酶可能采用同樣的催化反應(yīng)機(jī)制,。
這一研究成果將有助于人們進(jìn)一步理解不同類型的谷胱甘肽轉(zhuǎn)移酶之間的進(jìn)化關(guān)系，以及它們?cè)隗w內(nèi)的不同生物學(xué)功能,。（生物谷Bioon.com）
生物谷推薦原文出處：
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.
