Engineering the way to selective inhibition of human Nav1.7: a target for pain

Human voltage gated sodium (hNav) channels have been implicated in a multitude of debilitating cardiovascular and neurological disorders. The high degree of sequence identity shared by the nine human Nav channel isoforms present a significant challenge in designing selective channel blockers. These Nav channels also remain recalcitrant to high-resolution structural studies because of their dynamic and complex multi-domain architecture. By exploiting the established portability of the voltage-sensor domains (VSDs) and the evolutionary relationship between human and homotetrameric bacterial Nav channels, we have established a robust protein-engineering strategy that has allowed us first ever insights into the molecular structure of the fourth VSD (VSD4) domain from hNav1.7 in complex with isoform-selective small molecule antagonists. hNav1.7 is essential for pain perception and hence serves as an attractive target for development of novel analgesics. GX-936 and related inhibitors bind to the activated state of VSD4, where their anionic aryl sulfonamide warhead engages the fourth arginine gating charge on the S4 helix. These antagonists inhibit Nav1.7 through a ?voltage sensor trapping? mechanism by opposing the deactivation of VSD4, which in turn stabilizes inactivated states of the channel. Our structure reveals non-conserved residues on the S2 and S3 helices of hNav1.7 (VSD4) that form key determinants of isoform selectivity. In addition, we have observed a unique tripartite phospholipid-antagonist-VSD4 interaction, which furthers the role of membrane bilayers in modulating ion channel function and pharmacology. Our results shed light on the molecular basis of voltage sensing and establish a structural blueprint to design selective Nav channel antagonists for treating pain and other diseases