Department of Neurobiology, University of Chicago, Chicago, IL, USA.
Department of Biochemistry and Molecular Biology, University of Chicago, Chicago, IL, USA.
Nat Commun. 2023 Aug 21;14(1):5072. doi: 10.1038/s41467-023-40514-4.
The hinged-lid model was long accepted as the canonical model for fast inactivation in Nav channels. It predicts that the hydrophobic IFM motif acts intracellularly as the gating particle that binds and occludes the pore during fast inactivation. However, the observation in recent high-resolution structures that the bound IFM motif is located far from the pore, contradicts this preconception. Here, we provide a mechanistic reinterpretation of fast inactivation based on structural analysis and ionic/gating current measurements. We demonstrate that in Nav1.4 the final inactivation gate is comprised of two hydrophobic rings at the bottom of S6 helices. These rings function in series and close downstream of IFM binding. Reducing the volume of the sidechain in both rings leads to a partially conductive, leaky inactivated state and decreases the selectivity for Na ion. Altogether, we present an alternative molecular framework to describe fast inactivation.
铰链盖模型长期以来被认为是 Nav 通道快速失活的典型模型。它预测疏水性 IFM 基序在细胞内充当门控粒子，在快速失活过程中结合并阻塞孔道。然而，最近在高分辨率结构中的观察结果表明，结合的 IFM 基序位于远离孔道的位置，这与这种先入为主的观念相矛盾。在这里，我们基于结构分析和离子/门控电流测量提供了一种对快速失活的机制重新解释。我们证明在 Nav1.4 中，最终失活门由 S6 螺旋底部的两个疏水性环组成。这些环串联工作，并在 IFM 结合的下游关闭。减小两个环中侧链的体积会导致部分导通、渗漏失活状态，并降低对 Na 离子的选择性。总之，我们提出了一种替代的分子框架来描述快速失活。
