Molecular Determinants of C-type Inactivation for the hERG Channel and Its Disease-associated Mutants

Abstract

C-type inactivation is a time-dependent process observed in many K+ channels whereby prolonged activation by an external stimulus leads to a reduction in ionic conduction. The extremely fast C-type inactivation of the voltage-gated potassium channel hERG plays a critical role in the repolarization of cardiac cells, with malfunction having a direct impact on human health. For instance, a number of mutations in hERG have been identified to cause various forms of Long/Short QT Syndromes. Yet, understanding at the molecular level is limited, as the conformational change underlying C-type inactivation in the hERG channel has remained elusive. Molecular dynamics simulations show that the fast C-type inactivation in hERG is associated with an asymmetrical constricted-like conformation of the selectivity filter. Furthermore, molecular dynamics free energy landscape calculations reveal the molecular basis for the functional behavior for several disease-associated or functionally documented mutations, i.e., N628D, S631A, F627Y, S620T, and G628C/S631C. The high correlation between the functional data and the calculated free energy landscapes strongly supports the conclusions drawn from the simulations. The simulations point to several key residue-residue contacts responsible for the structural and functional impact of these mutations. The broader significance of one of these key contacts is then confirmed in protein sequence coevolution analysis based on a large number of sequences, supporting the notion that the features underlying C-type inactivation in hERG are universally conserved within the potassium channels family.