# Closed State Structure of the Pore Revealed by Uncoupled Shaker K+ Channel

## TL;DR

Scientists discovered a new closed state structure of the Shaker potassium channel using a modified version that reveals how the channel's pore closes.

## Contribution

The study reveals a novel closed pore structure of the Shaker K+ channel through an uncoupling mutation and cryoEM.

## Key findings

- The uncoupled I384R mutant Shaker channel shows a fully closed pore with activated voltage sensors.
- Pore closure involves a 'roll and turn' movement of S6 helices, differing from traditional models.
- A noncanonical selectivity filter conformation was observed at G446, distinct from known states.

## Abstract

Voltage gated potassium (Kv) channels play key roles in physiological processes, from cellular excitability to immune response and are among the most important pharmaceutical targets1. Despite recent advances in the structural determination of Kv channels, the closed state structure of strictly coupled Kv1 family remains elusive. Here, we captured the structure of Shaker potassium channel with a closed pore by uncoupling its voltage sensor domains from the pore domains. Structural determination of the uncoupled I384R mutant by single particle cryoEM revealed a fully closed pore in the presence of activated, non-relaxed voltage sensors. Putative conformational transitions estimated from a fully open pore domain indicates a “roll and turn” movement along the length of the pore-forming S6 helices, in sharp contrast to canonical gating models based on limited movements of S6 2–4. These rotational and translational movement place two hydrophobic residues, one at inner cavity and the other at the bundle crossing region, directly at the permeation pathway, limiting the pore radius to less than 1 Å. Surprisingly, the selectivity filter was captured in a noncanonical state, partially expanded at G446, unlike previously described dilated5 or pinched6 filter conformations. Based on the present data we propose a reinterpretation of the mechanism of activation gating for strictly coupled Kv1 channels and the strictly coupled interactions that underlie different functional states.