Structural mechanism of voltage-gated sodium channel slow inactivation.

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.