Structural mechanism of voltage-gated sodium channel slow inactivation.

Voltage-gated sodium (Na) channels mediate a plethora of electrical activities. Na channels govern cellular excitability in response to depolarizing stimuli. Inactivation is an intrinsic property of Na 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 channel slow inactivation remains elusive. Here, we demonstrate that the removal of the N-helix of NaEh (NaEh) results in a slow-inactivated channel, and present cryo-EM structure of NaEh 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 NaEh structure, NaEh undergoes marked conformational shifts on the intracellular side. Together, our results provide important mechanistic insights into Na channel slow inactivation.