Cardiovascular Research Institute, University of California, San Francisco, CA, USA.
Department of Molecular Medicine, University of Pavia, Pavia, Italy.
Nat Struct Mol Biol. 2022 Jun;29(6):537-548. doi: 10.1038/s41594-022-00775-x. Epub 2022 Jun 2.
Every voltage-gated ion channel (VGIC) has a pore domain (PD) made from four subunits, each comprising an antiparallel transmembrane helix pair bridged by a loop. The extent to which PD subunit structure requires quaternary interactions is unclear. Here, we present crystal structures of a set of bacterial voltage-gated sodium channel (BacNa) 'pore only' proteins that reveal a surprising collection of non-canonical quaternary arrangements in which the PD tertiary structure is maintained. This context-independent structural robustness, supported by molecular dynamics simulations, indicates that VGIC-PD tertiary structure is independent of quaternary interactions. This fold occurs throughout the VGIC superfamily and in diverse transmembrane and soluble proteins. Strikingly, characterization of PD subunit-binding Fabs indicates that non-canonical quaternary PD conformations can occur in full-length VGICs. Together, our data demonstrate that the VGIC-PD is an autonomously folded unit. This property has implications for VGIC biogenesis, understanding functional states, de novo channel design, and VGIC structural origins.
每种电压门控离子通道（VGIC）都有一个由四个亚基组成的孔域（PD），每个亚基由一对反向平行的跨膜螺旋桥接一个环组成。PD 亚基结构需要四级相互作用的程度尚不清楚。在这里，我们展示了一组细菌电压门控钠离子通道（BacNa）“仅孔”蛋白的晶体结构，揭示了一系列令人惊讶的非典型四级排列，其中 PD 三级结构得以维持。这种与上下文无关的结构稳健性得到了分子动力学模拟的支持，表明 VGIC-PD 三级结构独立于四级相互作用。这种折叠发生在整个 VGIC 超家族以及各种跨膜和可溶性蛋白中。引人注目的是，PD 亚基结合 Fab 的特性表明，非典型的四级 PD 构象可以出现在全长 VGIC 中。总之，我们的数据表明 VGIC-PD 是一个自主折叠的单元。这一特性对 VGIC 的生物发生、功能状态的理解、从头设计通道以及 VGIC 的结构起源具有重要意义。
