A gating hinge in Na⁺ channels: A molecular switch for electrical signaling

Voltage-gated sodium channels are members of a large family with similar pore structures. The mechanism of opening and closing is unknown, but structural studies suggest gating via bending of the inner pore helix at a glycine hinge. Here we provide functional evidence for this gating model for the bacterial sodium channel NaChBac. Mutation of glycine 219 to proline, which would strongly favor bending of the α helix, greatly enhances activation by shifting its voltage dependence -51 mV and slowing deactivation by 2000-fold. The mutation also slows voltage-dependent inactivation by 1200-fold. The effects are specific because substitutions of proline at neighboring positions and substitutions of other amino acids at position 219 have much smaller functional effects. Our results fit a model in which concerted bending at glycine 219 in the S6 segments of NaChBac serves as a gating hinge. This gating motion may be conserved in most members of this large ion channel protein family.