Ion Permeation in Potassium Selective and Non-selective Cation Channels

尽管有一个共同的架构，某些四聚体离子通道已经发展到选择不同的阳离子之间具有高特异性，而其他几乎没有选择性。这些不同的渗透特性的动力学和化学仍然知之甚少脊椎动物的离子通道。我们建议检查在这样的通道，在认知，感觉转导，和心脏节律的重要作用，与分子动力学模拟和功能实验紧密结合的离子运输。在AMPA型谷氨酸受体，我们将检查Ca 2+渗透和块，在脊椎动物大脑中的生物学关键过程。我们将使用最近推出的琥珀色和CHARMM兼容参数的钙离子。我们将验证这些结果与量子力学/分子力学（QM/MM）模拟。与AMPA通道一样，环核苷酸门控（CNG）通道在一价阳离子中是非选择性的。我们以前在细菌NaK通道中的工作揭示了K+传导需要4倍对称选择性过滤器（SF），而在Na+传导模拟中观察到不对称过滤器。我们将研究是否同样的机制也适用于CNG通道，视觉转导途径的关键组成部分。一个假定的开放结构的CNG通道现在已经成为可用的冷冻电子显微镜，使我们能够直接模拟K+和Na+的渗透在CNG channel.In我们的最终aim，我们将探讨结构对称性的离子SF和Na+/K+的选择性在K2 P通道之间的关系。TWIK-1通道是一种独特的K2 P通道，具有可变的离子选择性，预计会影响低钾血症下的心脏兴奋性。与其他K2 P信道相比，它具有高度非对称滤波器和非正则滤波器序列。TREK-1通道SF中的点突变，导致类似的不对称过滤器，引入异常的钠渗透性。在本项目中，我们将研究TWIK-1和TREK-1突变体的离子选择性的可变性机制，其通过小分子BL-1249的逆转，以及其与SF的对称性和动力学的相关性。

Despite a common architecture, certain tetrameric ion channels have evolved to select between different cations with high specificity, whereas others are barely selective. The dynamics and chemistry of these diverse permeation characteristics remain poorly understood for vertebrate ion channels. We propose to examine ion transport in such channels that have essential roles in cognition, sensory transduction, and cardiac rhythm, with a closely-knit combination of molecular dynamics simulations and functional experiments.In the AMPA-type glutamate receptor, we will examine Ca2+ permeation and block, a biologically critical process in the vertebrate brain. We will use recently introduced AMBER- and CHARMM-compatible parameters for Ca2+ ions. We will validate these results with quantum mechanics/molecular mechanics (QM/MM) simulations. Like the AMPA channel, the cyclic nucleotide- gated (CNG) channel is non-selective among monovalent cations. Our previous work in the bacterial NaK channel has revealed that K+-conduction requires a 4-fold symmetric selectivity filter (SF), while an asymmetric filter was observed in Na+-conducting simulations. We will investigate whether the same mechanism also applies to the CNG channel, a crucial component of the visual transduction pathway. A putative open structure of the CNG channel has now become available by cryo-electron microscopy, enabling us to directly simulate K+ and Na+ permeation in the CNG channel.In our final aim, we will probe the relationship between structural symmetry in the ion SF and Na+/K+ selectivity in K2P channels. The TWIK-1 channel is a unique K2P channel with variable ion selectivity, which is expected to impact cardiac excitability under hypokalemia. Compared to other K2P channels, it has a highly asymmetric filter and non-canonical filter sequence. A point mutation in the SF of the TREK-1 channel, resulting in a similar asymmetric filter, introduces aberrant sodium permeability. Within this project, we will investigate the mechanism of variability in the ion selectivity of TWIK-1 and the TREK-1 mutant, its reversion by the small molecule BL-1249, and its correlation to symmetry and dynamics of the SF.