The ClC-type proteins, a large family of chloride transport proteins ubiquitously expressed in biological organisms, have been extensively studied for decades. Biological function of ClC proteins can be reflected by analyzing the binding situation of Cl− ions. We investigate ion binding properties of ClC-ec1 protein with the atomic molecular dynamics simulation approach. The calculated electrostatic binding energy results indicate that Cl− at the central binding site Scen has more binding stability than the internal binding site Sint. Quantitative comparison between the latest experimental heat release data isothermal titration calorimetry (ITC) and our calculated results demonstrates that chloride ions prefer to bind at Scen than Sint in the wild-type ClC-ec1 structure and prefer to bind at Sext and Scen than Sint in mutant E148A/E148Q structures. Even though the chloride ions make less contribution to heat release when binding to Sint and are relatively unstable in the Cl− pathway, they are still part contributors for the Cl− functional transport. This work provides a guide rule to estimate the importance of Cl− at the binding sites and how chloride ions have influences on the function of ClC proteins.

中文翻译：

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决定 ClC 蛋白功能转运的离子结合能

ClC 型蛋白质是一个大家族的氯离子转运蛋白，广泛存在于生物有机体中，几十年来已被广泛研究。ClC 蛋白的生物学功能可以通过分析 Cl− 离子的结合情况来反映。我们用原子分子动力学模拟方法研究了 ClC-ec1 蛋白的离子结合特性。计算出的静电结合能结果表明中央结合位点 Scen 处的 Cl- 比内部结合位点 Sint 具有更高的结合稳定性。最新的实验放热数据等温滴定量热法 (ITC) 与我们的计算结果之间的定量比较表明，在野生型 ClC-ec1 结构中，氯离子更喜欢在 Scen 处结合而不是在 Sint 处结合，并且在突变 E148A/E148Q 结构。尽管氯离子在与 Sint 结合时对热释放的贡献较小，并且在 Cl− 途径中相对不稳定，但它们仍然是 Cl− 功能传输的部分贡献者。这项工作提供了一个指导规则来估计 Cl− 在结合位点的重要性以及氯离子如何影响 ClC 蛋白的功能。