Noncanonical electromechanical coupling paths in the cardiac hERG channel.

Abstract

The human ether-a-go-go-related gene (hERG) codes for a Kv channel involved in the delayed rectifier current that determines the plateau period of the cardiac action potential. During the cardiac action potential, this channel rapidly recovers from inactivation, to cease the action potential. hERG displays marked inward rectification, a mechanism due to an extremely fast pore inactivation and shown not to be related to the activation process. Moreover, hERG operates seamlessly without a covalent interaction between the voltage sensor (VSD) and the pore (PD), suggesting the presence of an alternative communication between VSD and PD, without the S4-S5 linker. Such mechanism has been shown in Shaker K+ channel, a domain-swapped channel, but it is yet to be determined in non-domain-swapped channels, like hERG. Here, we used a combination of mutagenesis and molecular dynamics simulations/network analysis to identify a chain of residues coupling the VSD to PD that involves S4∴S1 and S1∴S5 subunit interfaces. The role of each residue (T425, P426, A527, H562, W563, A565, W568, A614, Y616, F617, and T618) in the identified noncanonical paths was quantified by performing betweenness centrality analysis and tested using electrophysiological assays combined with leucine-scanning mutagenesis. To provide unequivocal evidence of the noncanonical path and the agreement between the computational prediction and experimental data, we plotted the betweenness centrality and the minimal distance of each mutant along the noncanonical paths against the free-energy perturbation of activation and of inactivation. These plots showed a good agreement between computational and experimental results, demonstrating that the residues identified are part of the noncanonical electromechanical coupling in hERG. Altogether, our work identifies the presence of allosteric, noncanonical gating paths in the hERG channel and shed new light on the elusive activation and inactivation mechanisms of non-domain-swapped channels. Support: NIH-GM030376, ERC:803213.