Ion Permeation in Potassium Selective and Non-selective Cation Channels

尽管有一个共同的结构，某些四聚体离子通道已经进化到在不同的阳离子之间进行高度特异性的选择，而其他的几乎没有选择性。对于脊椎动物的离子通道，这些不同的渗透特性的动力学和化学仍然知之甚少。我们建议通过分子动力学模拟和功能实验的紧密结合来研究在认知、感觉转导和心律中起关键作用的这些通道中的离子传输。在AMPA型谷氨酸受体中，我们将检测钙离子的渗透和阻断，这是脊椎动物大脑中的一个生物学关键过程。我们将使用最近推出的与琥珀和CHARMM兼容的参数来处理钙离子。我们将用量子力学/分子力学(QM/MM)模拟来验证这些结果。与AMPA通道一样，环核苷酸门控(CNG)通道在单价阳离子中是非选择性的。我们以前在细菌NaK通道中的工作表明，K+传导需要4倍对称选择性过滤器(SF)，而在Na+传导模拟中观察到非对称过滤器。我们将研究同样的机制是否也适用于CNG通道，这是视觉转导通路的关键组成部分。通过低温电子显微镜，我们可以直接模拟K+和Na+在CNG通道中的渗透。在我们的最终目标中，我们将探索离子SF的结构对称性与K2P通道中Na+/K+选择性之间的关系。Twik-1通道是一种独特的具有可变离子选择性的K2P通道，它有望在低钾血症下影响心脏的兴奋性。与其他K2P信道相比，它具有高度不对称的滤波和非规范的滤波序列。Trek-1通道SF中的一个点突变导致了类似的不对称过滤器，导致了异常的钠通透性。在这个项目中，我们将研究twik-1和Trek-1突变体的离子选择性变化的机制，它被小分子BL-1249逆转，以及它与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.