Crystal structure of a voltage-gated sodium channel in two potentially inactivated states

Abstract

In excitable cells, voltage-gated sodium (NaV) channels activate to initiate action potentials and then undergo fast and slow inactivation processes that terminate their ionic conductance. Inactivation is a hallmark of NaV channel function and is critical for control of membrane excitability, but the structural basis for this process has remained elusive. Here we report crystallographic snapshots of the wild-type NaVAb channel from Arcobacter butzleri captured in two potentially inactivated states at 3.2 Å resolution. Compared to previous structures of NaVAb channels with cysteine mutations in the pore-lining S6 helices (ref. 4), the S6 helices and the intracellular activation gate have undergone significant rearrangements: one pair of S6 helices has collapsed towards the central pore axis and the other S6 pair has moved outward to produce a striking dimer-of-dimers configuration. An increase in global structural asymmetry is observed throughout our wild-type NaVAb models, reshaping the ion selectivity filter at the extracellular end of the pore, the central cavity and its residues that are analogous to the mammalian drug receptor site, and the lateral pore fenestrations. The voltage-sensing domains have also shifted around the perimeter of the pore module in wild-type NaVAb, compared to the mutant channel, and local structural changes identify a conserved interaction network that connects distant molecular determinants involved in NaV channel gating and inactivation. These potential inactivated-state structures provide new insights into NaV channel gating and novel avenues to drug development and therapy for a range of debilitating NaV channelopathies.