Enescu Mironel, Kassim Rima, Ramseyer Christophe, Cardey Bruno
Laboratoire Chrono Environnement UMR CNRS 6249, University of Franche-Comté, 16 route de Gray, 25030, Besançon Cedex, France,
J Biol Inorg Chem. 2015 Apr;20(3):555-62. doi: 10.1007/s00775-015-1240-z. Epub 2015 Jan 31.
Heat shock protein 33 (Hsp33) is activated in the presence of H2O2 by a very interesting redox switch based on a tetra-coordinated zinc-cysteine complex present in the fully reduced and inactive protein form. The oxidation of this zinc center by H2O2 induces formation of two S-S bridges and the zinc release followed by the protein unfolding. We report here a theoretical study of the step-by-step sequence of the overall process starting with the oxidation of the first cysteine residue and ending with the zinc release. Each reaction step is characterized by its Gibbs free energy barrier (∆G (‡)). It is predicted that the first reaction step consists in the oxidation of Cys263 by H2O2 which is by far the most reactive cysteine (∆G (‡) = 15.4 kcal mol(-1)). The next two reaction steps are the formation of the first S-S bridge between Cys263 and Cys266 (∆G (‡) = 13.6 kcal mol(-1)) and the oxidation of Cys231 by H2O2 (∆G (‡) = 20.4 kcal mol(-1)). It is then shown that the formation of the second S-S bridge (Cys231-Cys233) before the zinc release is most unlikely (∆G (‡) = 34.8 kcal mol(-1)). Instead, the release of zinc just after the oxidation of the third cysteine (Cys231) is shown to be thermodynamically (dissociation Gibbs free energy ∆G d = 6.0 kcal mol(-1)) and kinetically (reaction rate constant k d ≈ 10(6) s(-1)) favored. This result is in good agreement with the experimental data on the oxidation mechanism of Hsp33 zinc center available to date.
热休克蛋白33（Hsp33）在过氧化氢存在的情况下，通过一个非常有趣的氧化还原开关被激活，该开关基于完全还原且无活性的蛋白质形式中存在的四配位锌-半胱氨酸复合物。过氧化氢对这个锌中心的氧化诱导形成两个S-S桥，并导致锌释放，随后蛋白质展开。我们在此报告对整个过程逐步序列的理论研究，该过程从第一个半胱氨酸残基的氧化开始，到锌释放结束。每个反应步骤都以其吉布斯自由能垒（∆G(‡)）为特征。据预测，第一个反应步骤是过氧化氢氧化Cys263，Cys263是迄今为止反应性最强的半胱氨酸（∆G(‡)=15.4千卡·摩尔⁻¹）。接下来的两个反应步骤是Cys263和Cys266之间形成第一个S-S桥（∆G(‡)=13.6千卡·摩尔⁻¹）以及过氧化氢氧化Cys231（∆G(‡)=20.4千卡·摩尔⁻¹）。然后表明，在锌释放之前形成第二个S-S桥（Cys231-Cys233）的可能性极小（∆G(‡)=34.8千卡·摩尔⁻¹）。相反，在第三个半胱氨酸（Cys231）氧化后紧接着锌的释放，在热力学上（解离吉布斯自由能∆Gd = 6.0千卡·摩尔⁻¹）和动力学上（反应速率常数kd≈10⁶秒⁻¹）都是有利的。这一结果与迄今为止可得的关于Hsp33锌中心氧化机制的实验数据高度吻合。
