Pathological turret mutations in the cardiac sodium channel cause long-range pore disruption

Abstract

The voltage-gated sodium channel Nav1.5 initiates the cardiac action potential. Germline mutations that disrupt Nav1.5 activity predispose affected individuals to inherited cardiopathologies. Some of these Nav1.5 mutations alter amino acids in extracellular turret domains DII and DIII. Yet the mechanism is unclear. In the rat Nav1.5 structure determined by cryogenic electron microscopy, the wild-type residues corresponding to these mutants form a complex salt-bridge between the DII and DIII turret interface. Furthermore, adjacent aromatic residues form cation-{pi} interactions with the complex salt-bridge. Here, we examine this region using site-directed mutagenesis, electrophysiology and in silico modeling. We confirm functional roles for the salt-bridges and the aromatic residues. We show that their disruption perturbs the geometry of both the DEKA selectivity ring and the inner pore vestibule that are crucial for sodium ion permeability. Our findings provide insights into a class of pathological mutations occurring not only in Nav1.5 but also in other sodium channel isoforms too. Our work illustrates how the sodium channel structures now being reported can be used to formulate and guide novel functional hypotheses.