SPM binding and pore block. (A) Ion permeation events per unit time under depolarizing (Sims. 31–46, blue) and hyperpolarizing (Sims. 51–58, red) conditions, and in the presence of SPM. Inset: Molecular structure of SPM. (B) Ion transitions across the SF (top) and SPM position relative to the D173 center of mass (C_α atoms; bottom) at three different depolarizing voltages (Sims. 48, 39, and 32). (C) Simulation snapshots (Sim. 39) revealing sequential SPM (in cyan) binding resulting in pore block, with potassium ions individually colored. (D) Voltage-dependent SPM binding (Fig. S4 A) and SPM residence times at the pore cavity-SF region (bottom; Sims. 31–46). (E) Ion permeation events as a function of simulation time in the presence (red, Sim. 47) and absence (black, Sim. 12) of SPM at low voltage (155 mV), where SPM is only weakly bound, and mostly to the CTD.