使用分子模拟研究电压门控钠离子通道的分子机理

Voltage-gated sodium (Nav) channels play essential roles in numerous biological activities, especially in the neuronal signaling. Dysfunction of the Nav channels typically leads to severe diseases including the epileptic seizures and cardiac arrhythmias. The proper function of Nav channels depends on two key properties of them: ion selection and voltage gating. The former characteristic requires the Nav channels to selectively control the transmembrane permeation of cations with similar chemical property (e.g., sodium and potassium ions), while the latter one allows those channels to open and close at various transmembrane electric potentials. Despite the successive determination of the crystal structures of four prokaryotic Nav channels, the molecular mechanism of neither ion selectivity nor voltage gating of mammalian Nav channels can be clearly illustrated solely from the static crystal structures, even if the sequence difference between prokaryotic and eukaryotic channels are neglected. In this project, we plan to elaborately explore the mechanism of ion selection and voltage gating in mammalian Nav channels. Starting from the prokaryotic crystal structures, we first mutate the key residues to model the structure of their mammalian counterparts, and then simulate the dynamics of these channels in silico. By combining equilibrium simulation and thermodynamic calculation, we hope to propose a molecular model to interpret how the Nav channels successfully discriminate sodium and potassium ions and how these channels change their conformations in response to the variation of transmembrane electric potentials. Additionally, we plan to study the interacting modes between some small antagonists and Nav channels, which may benefit the future drug development in treating the diseases related with the dysfunction of these channels.

电压门控钠离子（Nav）通道在神经信号传导中起重要作用。其功能丧失会导致诸如癫痫和心律失常等严重疾病。Nav通道正常行使功能需要其具备两个重要特性，即离子选择性和电压门控特性。离子选择性要求通道区别化学上相似的阳离子，电压门控特性则允许通道在不同跨膜电压下发生构象变化。虽然近年来陆续解析出四种原核生物Nav通道的晶体结构，但是这些静态的晶体结构很难给出足够的信息去揭示哺乳动物中Nav通道产生离子选择性和门控特性的分子机理。在本项目中，我们计划详细研究哺乳动物Nav通道的离子选择性和门控特性。从原核晶体结构出发，我们首先通过定点突变建立哺乳动物中相应通道的结构模型，然后通过计算机模拟研究其动态特性。通过结合平衡模拟与热力学计算，我们希望能提出合理的分子模型，阐释离子选择性和电压门控特性的分子机理。此外，我们还计划研究某些小分子拮抗剂与Nav通道的作用模式，从而指导将来的相关药物设计。

电压门控钠离子（Nav）通道在神经信号传导中起重要作用。Nav通道正常行使功能需要其具备两个重要特性，即离子选择性和电压门控特性。虽然近年来陆续解析出四种原核生物Nav通道的晶体结构，但是这些静态的晶体结构很难给出足够的信息去揭示哺乳动物中Nav通道产生离子选择性和门控特性的分子机理。在本项目中，我们使用分子动力学模拟详细研究了哺乳动物Nav通道的离子选择性和门控特性。从原核结构NavRh出发，我们首先搭建了DEKA和DERA突变体并研究了哺乳动物中DEKA模式对离子扩散和选择性的影响。我们发现，DEKA中的赖氨酸对维持离子选择性是必需的，将其突变为同源的精氨酸仍然会破会选择性。其原因是精氨酸侧链具有平面结构，而且正电荷分布较稀疏。此外，我们构建了开放的NavRh结构，并通过模拟离子转运过程成功预测了通道的电导。我们发现DEKA模式可以有效提高转运离子间的偶联，从而提高通道的离子转运效率。最后，我们研究了原核NavAb通道的电压感应结构域在通道激活时其构象变化过程。根据模拟轨迹，我们确定了反应路径，并严格计算了沿路径的自由能变化。