The S4–S5 Linker Acts as a Signal Integrator for hERG K+ Channel Activation and Deactivation Gating

Chai Ann Ng,Peter S Tan,Jamie I Vandenberg,Philip W Kuchel,Matthew D Perry,Adam P Hill,Bernard Attali

doi:10.1371/journal.pone.0031640

Abstract

Human ether-à-go-go-related gene (hERG) K+ channels have unusual gating kinetics. Characterised by slow activation/deactivation but rapid inactivation/recovery from inactivation, the unique gating kinetics underlie the central role hERG channels play in cardiac repolarisation. The slow activation and deactivation kinetics are regulated in part by the S4–S5 linker, which couples movement of the voltage sensor domain to opening of the activation gate at the distal end of the inner helix of the pore domain. It has also been suggested that cytosolic domains may interact with the S4–S5 linker to regulate activation and deactivation kinetics. Here, we show that the solution structure of a peptide corresponding to the S4–S5 linker of hERG contains an amphipathic helix. The effects of mutations at the majority of residues in the S4–S5 linker of hERG were consistent with the previously identified role in coupling voltage sensor movement to the activation gate. However, mutations to Ser543, Tyr545, Gly546 and Ala548 had more complex phenotypes indicating that these residues are involved in additional interactions. We propose a model in which the S4–S5 linker, in addition to coupling VSD movement to the activation gate, also contributes to interactions that stabilise the closed state and a separate set of interactions that stabilise the open state. The S4–S5 linker therefore acts as a signal integrator and plays a crucial role in the slow deactivation kinetics of the channel.

Highlights

The human ether-a-go-go-related gene encodes a voltagegated K+ channel, which passes a major repolarising current [1,2] during the cardiac action potential [3]
These unusual gating kinetics are critical both for the role human ether-a-go-go-related gene (hERG) channels play in normal cardiac repolarisation [3] as well as in suppression of premature beats in the period surrounding the termination of the action potential [5,6]
Solution structure of hERG S4–S5 linker An alignment of the S4–S5 linker region of hERG and Kv1.2 is shown in Fig. 1A with the peptide sequence used for structural studies shown in bold text

Summary

Introduction

The human ether-a-go-go-related gene (hERG) encodes a voltagegated K+ channel, which passes a major repolarising current (termed IKr) [1,2] during the cardiac action potential [3]. HERG channels have unusual gating kinetics characterised by slow transitions between the open and closed states but much more rapid transitions between the open and inactivated states [4,5] These unusual gating kinetics are critical both for the role hERG channels play in normal cardiac repolarisation [3] as well as in suppression of premature beats in the period surrounding the termination of the action potential [5,6]. Studies of hERG K+ channels have confirmed that each of these elements; the VSD [9,10,11], S4–S5 linker [12,13] and distal pore domain [14] play important roles in activation and deactivation gating of hERG channels. There has not, been a systematic and comprehensive analysis of the effects of mutations throughout the S4–S5 linker

Methods

Results

Conclusion