MicroED structure of the NaK ion channel reveals a Na⁺ partition process into the selectivity filter.

ABSTRACT: Sodium (Na⁺) is a ubiquitous and important inorganic salt mediating many critical biological processes such as neuronal excitation, signaling, and facilitation of various transporters. The hydration states of Na⁺ are proposed to play critical roles in determining the conductance and the selectivity of Na⁺ channels, yet they are rarely captured by conventional structural biology means. Here we use the emerging cryo-electron microscopy (cryoEM) method micro-electron diffraction (MicroED) to study the structure of a prototypical tetrameric Na⁺-conducting channel, NaK, to 2.5 Å resolution from nano-crystals. Two new conformations at the external site of NaK are identified, allowing us to visualize a partially hydrated Na⁺ ion at the entrance of the channel pore. A process of dilation coupled with Na⁺ movement is identified leading to valuable insights into the mechanism of ion conduction and gating. This study lays the ground work for future studies using MicroED in membrane protein biophysics.

SUBMITTER: Liu S 

PROVIDER: S-EPMC6112790 | biostudies-literature | 2018

REPOSITORIES: biostudies-literature