Structural basis for high-voltage activation and subtype-specific inhibition of human Na1.8.

The dorsal root ganglia-localized voltage-gated sodium (Na) channel Na1.8 represents a promising target for developing next-generation analgesics. A prominent characteristic of Na1.8 is the requirement of more depolarized membrane potential for activation. Here we present the cryogenic electron microscopy structures of human Na1.8 alone and bound to a selective pore blocker, A-803467, at overall resolutions of 2.7 to 3.2 Å. The first voltage-sensing domain (VSD) displays three different conformations. Structure-guided mutagenesis identified the extracellular interface between VSD and the pore domain (PD) to be a determinant for the high-voltage dependence of activation. A-803467 was clearly resolved in the central cavity of the PD, clenching S6. Our structure-guided functional characterizations show that two nonligand binding residues, Thr397 on S6 and Gly1406 on S6, allosterically modulate the channel's sensitivity to A-803467. Comparison of available structures of human Na channels suggests the extracellular loop region to be a potential site for developing subtype-specific pore-blocking biologics.