# Two-step voltage-sensor activation of the human KV7.4 channel and effect of a deafness-associated mutation

## TL;DR

This study investigates how KV7.4 potassium channels in the inner ear open and how a specific mutation linked to hearing loss disrupts this process.

## Contribution

The study reveals a two-step voltage-sensor activation mechanism in KV7.4 channels and how a deafness-associated mutation affects this process.

## Key findings

- KV7.4 voltage-sensor activation involves multiple voltage-dependent transitions, some matching the kinetics of channel opening.
- The R216H mutation impairs VSD movement and channel opening by destabilizing the active VSD configuration.
- Molecular dynamics simulations confirm the mutation's effect on VSD destabilization.

## Abstract

KCNQ4-encoded KV7.4 voltage-gated potassium channels are expressed in hair-cells of the inner ear. Loss-of-function variants in KCNQ4 cause non-syndromic progressive hearing loss (DFNA2). KV7.4 pore opening requires voltage-dependent conformational changes (activation) of the voltage-sensor domains (VSDs); however, how fast charge displacement during VSD activation is coupled to slow channel opening is currently unclear. Here, we optically tracked KV7.4 VSD activation with voltage-clamp fluorometry, leveraging two fluorophores and pulsed excitation, and found that VSD activation comprises several voltage-dependent transitions, some with kinetics and voltage-dependence matching those of channel opening and closing. The DFNA2-causing R216H mutation impairs VSD movement and channel opening by destabilizing the active VSD configuration, a result confirmed by molecular dynamics simulations. We propose that the KV7.4 VSD activates in two steps: a fast movement representing a first transition to an intermediate activation state, followed by slower component(s) that fully activate the VSD and drive channel opening.

Kv7.4 channels regulate auditory function. Here, authors use electrophysiological, optical and computational methods to investigate the structural changes that drive Kv7.4-channel opening, and how these are impaired by a deafness-causing mutation