Uncoupling sodium channel dimers rescues the phenotype of a pain‐linked Nav1.7 mutation

BACKGROUND & PURPOSE The voltage-gated sodium channel Nav1.7 is essential for adequate perception of painful stimuli. Mutations in the encoding gene, SCN9A, cause various pain syndromes in human patients. The hNav1.7/A1632E mutant causes symptoms of erythromelalgia and paroxysmal extreme pain disorder (PEPD), and its main gating change is a strongly enhanced persistent current. On the basis of recently published 3D structures of voltage-gated sodium channels, we investigated how the inactivation particle binds to the channel, how this mechanism is interfered with by the hNav1.7/A1632E mutation, and how dimerization modifies function of the pain-linked mutation. EXPERIMENTAL APPROACH We applied atomistic molecular simulations to demonstrate the effect of the mutation on channel fast inactivation. Native polyacrylamide gel electrophoresis (PAGE) was used to demonstrate channel dimerization and patch-clamp measurements revealed a link between functional channel dimerization and the impairment of fast inactivation by the hNav1.7/A1632E mutation. KEY RESULTS We demonstrate that the enhanced persistent current of hNav1.7/A1632E is due to impaired binding of the inactivation particle, which inhibits the proper function of the recently proposed allosteric fast inactivation mechanism. We show that hNav1.7 forms dimers and that the disease-associated persistent current of hNav1.7/A1632E depends on the channel's functional dimerization status: Expression of the synthetic peptide difopein, a 14-3-3 inhibitor known to functionally uncouple dimers, significantly decreased hNav1.7/A1632E-induced persistent currents. CONCLUSION Functional uncoupling of mutant hNav1.7/A1632E channel dimers rescues its defective allosteric fast inactivation mechanism. Our findings support the concept of sodium channel dimerization and reveal its potential relevance for human pain syndromes.