Structural basis of human Slo2.2 channel gating and modulation

The sodium-activated Slo2.2 channel is abundantly expressed in the brain, playing a critical role in regulating neuronal excitability. The Na+-binding site and the underlying mechanisms of Na+-dependent activation remain unclear. Here, we present cryoelectron microscopy (cryo-EM) structures of human Slo2.2 in closed, open, and inhibitor-bound form at resolutions of 2.6-3.2 A, revealing gating mechanisms of Slo2.2 regulation by cations and a potent inhibitor. The cytoplasmic gating ring domain of the closed Slo2.2 harbors multiple K+ and Zn2+ sites, which stabilize the channel in the closed conformation. The open Slo2.2 structure reveals at least two Na+-sensitive sites where Na+ binding induces expansion and rotation of the gating ring that opens the inner gate. Furthermore, a potent inhibitor wedges into a pocket formed by pore helix and S6 helix and blocks the pore. Together, our results provide a comprehensive structural framework for the investigation of Slo2.2 channel gating, Na+ sensation, and inhibition.