Identification of Residues Contributing to the VSD-PD Coupling in IKS Channels

Abstract

KCNQ1 and KCNE1 subunits together form the cardiac voltage-gated potassium IKs (KCNQ1/KCNE1) channel that regulates the repolarization of the ventricular action potential. Mutations in KCNQ1/KCNE1 channels are the most common cause of Long QT syndrome, which can cause cardiac arrhythmias and sudden cardiac deaths. The KCNQ1 subunit contains both a voltage-sensing domain (VSD) and a pore domain (PD). The opening of voltage-gated K+ channels generally involves three processes: movements in the VSD, the VSD-PD coupling, and activation of the PD. Although most studies have focused on the effects of KCNE1 on the voltage sensor and the pore of KCNQ1 channels, less attention has been paid to the role of KCNE1 in modulating the VSD-PD coupling. Objectives: This study seeks to identify residues that contribute to the VSD-PD coupling in KCNQ1/KCNE1 channels. It will give new insights into the modulations of KCNE1 on the KCNQ1 channel. The residues located at the VSD-PD interface were mutated to alanine one at a time. The mutant channel was expressed in Xenopus laevis oocytes. Voltage clamp fluorometry was conducted to simultaneously monitor the movement of the voltage-sensing domain (by fluorescence) and pore opening (by ionic current). We have found that some mutations change the VSD-PD coupling of KCNQ1/KCNE1 channels. These mutations partly abolish the effect of KCNE1 on the channel opening of KCNQ1 channels. Several residues lining the VSD-PD interface are highly important for the VSD-PD coupling in KCNQ1/KCNE1 channels. Identifying these residues is critical to elucidate the mechanism by which voltage sensor activation is coupled to channel opening in KCNQ1/KCNE1 channels. The study will help understanding why mutations at the VSD-PD interface cause cardiac arrhythmias and possibly lead to the design of novel anti-arrhythmic treatments to prevent sudden deaths.