Different roles for aspartates and glutamates for cation permeation in bacterial sodium channels
Different roles for aspartates and glutamates for cation permeation in bacterial sodium channels
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DOI：
10.1016/j.bbamem.2018.11.011
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发表时间：
2019-02-01
影响因子：
3.4
通讯作者：
Roberts, Stephen K.
中科院分区：
文献类型：
--
作者：
Guardiani, Carlo;Fedorenko, Olena A.;Roberts, Stephen K.
离子通道选择性的关键驱动力由天冬氨酸（D）和谷氨酸（E）残基携带的选择性过滤器的负电荷表示。然而，D和E残基的结构效应和特定性质尚未得到广泛研究。为了研究这个问题，我们研究了在位置191和192的带电环中具有D和E的所有可能组合的NaChBac通道的突变体。电生理测量显示，只有当位置191被E占据时才有显著的Ca 2+电流。平衡分子动力学模拟显示存在两个结合位点，对应于带电环和另一个，更多的内部，在L190的水平。模拟结果表明，只有当191位残基是谷氨酸时，最里面的离子才能与191位残基相互作用。基于MD模拟，我们认为，在位置191的D导致高亲和力的Ca2+块网站从一个显着下降的自由能的结合之间移动的结合位点的离子，相比之下，自由能的变化是更渐进的，当E残基占据位置191，导致Ca2+渗透性。这种情况与Dang和McCleskey提出的通过结合亲和力逐步变化的离子通道选择性模型一致。我们的研究还强调了选择性过滤器的结构的重要性，这将有助于开发更详细的离子通道选择性的物理模型。
A key driving force for ion channel selectivity is represented by the negative charge of the Selectivity Filter carried by aspartate (D) and glutamate (E) residues. However, the structural effects and specific properties of D and E residues have not been extensively studied. In order to investigate this issue we studied the mutants of NaChBac channel with all possible combinations of D and E in the charged rings in position 191 and 192. Electrophysiological measurements showed significant Ca2+ currents only when position 191 was occupied by E. Equilibrium Molecular Dynamics simulations revealed the existence of two binding sites, corresponding to the charged rings and another one, more internal, at the level of L190. The simulations showed that the ion in the innermost site can interact with the residue in position 191 only when this is glutamate. Based on the MD simulations, we suggest that a D in position 191 leads to a high affinity Ca2+ block site resulting from a significant drop in the free energy of binding for an ion moving between the binding sites; in contrast, the free energy change is more gradual when an E residue occupies position 191, resulting in Ca2+ permeability. This scenario is consistent with the model of ion channel selectivity through stepwise changes in binding affinity proposed by Dang and McCleskey. Our study also highlights the importance of the structure of the selectivity filter which should contribute to the development of more detailed physical models for ion channel selectivity.