Abstract
Voltage-gated sodium (Na(V)) channels mediate a plethora of electrical activities. Na(V) channels govern cellular excitability in response to depolarizing stimuli. Inactivation is an intrinsic property of Na(V) channels that regulates cellular excitability by controlling the channel availability. The fast inactivation, mediated by the Ile-Phe-Met (IFM) motif and the N-terminal helix (N-helix), has been well-characterized. However, the molecular mechanism underlying Na(V) channel slow inactivation remains elusive. Here, we demonstrate that the removal of the N-helix of Na(V)Eh (Na(V)Eh(ΔN)) results in a slow-inactivated channel, and present cryo-EM structure of Na(V)Eh(ΔN) in a potential slow-inactivated state. The structure features a closed activation gate and a dilated selectivity filter (SF), indicating that the upper SF and the inner gate could serve as a gate for slow inactivation. In comparison to the Na(V)Eh structure, Na(V)Eh(ΔN) undergoes marked conformational shifts on the intracellular side. Together, our results provide important mechanistic insights into Na(V) channel slow inactivation.