The human ether-à-go-go-related gene (hERG) potassium channel is a key contributor to cardiac repolarization, characterized by its unique gating kinetics of slow activation and rapid C-type inactivation. As in other Kv channels, voltage sensors in hERG move upon changes in the transmembrane electric field, with upward displacement coupled to channel activation. However, the structural basis of the hERG electromechanical coupling between sensor, gate and selectivity filter remains poorly understood. A single mutant in the S4-S5 linker, D540K, has been shown to confer hERG with an unusual dual gating polarity, as conductance increases both upon depolarizing and hyperpolarizing voltage changes. Here, we determined the cryo-EM structure of hERG D540K at 0 mV in detergent micelles. Compared to the wildtype hERG structure in its open-state, D540K displays a significant counterclockwise rotation of the voltage sensor domains (VSDs) relative to its pore domain. Based on this observation, we suggest that this rotation impinges upon the S4-S5 linker-S6 interface. Charge-swapping mutants, D540K/R665D and D540K/R665E, evaluated by whole cell patch clamp, reduced hyperpolarization-dependent reopening and restored native function of hERG channels. This suggests an important role for electrostatic interactions between D540 at the S4-S5 linker and R665 in the C-terminal end of S6 in stabilizing the closed conformation in the VSD down state. D540K would disrupt the S4-S5-S6 coupling via electrostatic repulsion with R665, thus flipping gating. Overall, our findings point to the importance of cooperativity between the S4-S5 linker and the S6 domain in modulating the gating polarity of hERG. Understanding the mechanisms behind the electromechanical decoupling could provide valuable insight into hERG’s physiological function and its potential clinical impacts on arrhythmias.
Tong et al. (Sun,) studied this question.