Centre for Molecular Simulation, Department of Biological Sciences, University of Calgary, Calgary, AB T2N 1N4, Canada.
Department of Physiology and Membrane Biology, University of California, Davis, CA 95616.
Proc Natl Acad Sci U S A. 2020 Feb 11;117(6):2795-2804. doi: 10.1073/pnas.1909196117. Epub 2020 Jan 24.
The human -related gene (hERG1) channel conducts small outward K currents that are critical for cardiomyocyte membrane repolarization. The gain-of-function mutation N629D at the outer mouth of the selectivity filter (SF) disrupts inactivation and K-selective transport in hERG1, leading to arrhythmogenic phenotypes associated with long-QT syndrome. Here, we combined computational electrophysiology with Markov state model analysis to investigate how SF-level gating modalities control selective cation transport in wild-type (WT) and mutant (N629D) hERG1 variants. Starting from the recently reported cryogenic electron microscopy (cryo-EM) open-state channel structure, multiple microseconds-long molecular-dynamics (MD) trajectories were generated using different cation configurations at the filter, voltages, electrolyte concentrations, and force-field parameters. Most of the K permeation events observed in hERG1-WT simulations occurred at microsecond timescales, influenced by the spontaneous dehydration/rehydration dynamics at the filter. The SF region displayed conductive, constricted, occluded, and dilated states, in qualitative agreement with the well-documented flickering conductance of hERG1. In line with mutagenesis studies, these gating modalities resulted from dynamic interaction networks involving residues from the SF, outer-mouth vestibule, P-helices, and S5-P segments. We found that N629D mutation significantly stabilizes the SF in a state that is permeable to both K and Na, which is reminiscent of the SF in the nonselective bacterial NaK channel. Increasing the external K concentration induced "WT-like" SF dynamics in N629D, in qualitative agreement with the recovery of flickering currents in experiments. Overall, our findings provide an understanding of the molecular mechanisms controlling selective transport in K channels with a nonconventional SF sequence.
人类相关基因（hERG1）通道传导外向的小 K 电流，这对于心肌细胞膜复极化至关重要。位于选择性滤器（SF）外口的功能获得性突变 N629D 破坏 hERG1 的失活和 K 选择性转运，导致与长 QT 综合征相关的致心律失常表型。在这里，我们结合计算电生理学和 Markov 状态模型分析，研究 SF 水平门控模式如何控制野生型（WT）和突变型（N629D）hERG1 变体中的选择性阳离子转运。从最近报道的低温电子显微镜（cryo-EM）开放态通道结构开始，使用滤器中的不同阳离子构型、电压、电解质浓度和力场参数，生成了多个微秒长的分子动力学（MD）轨迹。在 hERG1-WT 模拟中观察到的大多数 K 渗透事件发生在微秒时间尺度内，受滤器中自发去水/复水动力学的影响。SF 区域显示出传导、收缩、阻塞和扩张状态，与 hERG1 有充分记录的闪烁电导定性一致。与突变研究一致，这些门控模式源自涉及 SF、外口前庭、P-螺旋和 S5-P 段的动态相互作用网络。我们发现 N629D 突变显著稳定了 SF 状态，使其对 K 和 Na 都具有通透性，这让人联想到非选择性细菌 NaK 通道中的 SF。增加外部 K 浓度会诱导 N629D 中的“WT 样”SF 动力学，定性上与实验中闪烁电流的恢复一致。总的来说，我们的研究结果提供了对控制具有非常规 SF 序列的 K 通道选择性转运的分子机制的理解。
