Model of lipid-dependent activation mechanism and SPM pore block. Closed conformation: In the absence of negatively charged lipids, positively charged R/K residues near the activation gate engage in salt bridge interactions with negatively charged IH residues and TM1 backbone residues, thereby stabilizing the closed, deactivated channel conformation. Open conformation: In the presence of negatively charged PIP₂ and POPS lipid molecules in the membrane, three key sequential structural changes lead to pore opening and channel activation: (1) the R/K-rich region loses interaction with negatively charged IH residues in exchange for interactions with PIP₂ molecules at the primary lipid-binding site, which leads to disengagement of the IH from the pore domain, allowing the IH to move radially away from the pore axis; (2) the CTD then moves towards the pore domain and CTD residues R219 and K220 of the secondary lipid-binding site interact with POPS lipid molecules, permitting G-loop residue E304 to interact with the R/K-rich region; and (3) slight rotation and splaying of inner TM helices occurs, leading to pore opening. Blocked conformation: Under depolarizing conditions (V > 0), SPM (grey/blue) is recruited by the CTD and sequentially translocates toward the pore cavity-SF region, where it displaces approximately five cavity/SF-bound potassium ions as it binds above the D173 rectification controller, blocking the ion permeation pathway.