Figure 3. The activation gate and the pore in resting, activated, and inactivated states^7–10.

a, Solvent accessible surface of Na_VAb in the resting/closed state (left), adapted from¹⁰. Interactions between the S4-S5 linker and S6 near the activation gate in the resting state (right). b, Solvent accessible surface of Na_VAb in the activated/open state (left), adapted from¹⁰. Interactions between the S4-S5 linker and S6 near the activation gate in the activated state (right). The pore is tightly closed at the activation gate in the resting/closed state (red, panel a) but wide open in the activated/open state (green, panel b). The movement of the S4-S5 linker from the resting/closed state to the activated/open state unbends the elbow and causes an exchange of interactions between the S4-S5 linker residues (red) and the S6 residues (blue), which surround the activation gate formed by the S6 segments. c, Solvent accessible surface of Na_VAb in the slow-inactivated/closed state (left). Interactions between the S4-S5 linker and S6 near the activation gate in the slow-inactivated state (right). d, Structural transition between pre-open and inactivated states viewed in cross-section at three levels of the pore: top, ion selectivity filter; center S4 is green, central cavity; bottom, activation gate, adapted from⁸.