Asymmetric assembly underlies activation mechanism of neuronal GIRK1/2 channels

G protein-gated inwardly rectifying potassium (GIRK; Kir3) channels are principal effectors of inhibitory GPCR signaling. Here we combine cryo-electron microscopy, single-molecule imaging, electrophysiology and molecular dynamics to define the architecture and activation of neuronal GIRK1/2 channels. GIRK1/2 preferentially assembles as an asymmetric heterotetramer containing one GIRK1 and three GIRK2 subunits. Three PIP₂ molecules bound to GIRK2 promote partial cytoplasmic-domain docking, whereas engagement of a fourth PIP₂ by GIRK1 completes docking and opens the helix bundle crossing gate. GIRK1 also remodels the electrostatic environment beneath the selectivity filter, where its E141 and D173 residues create a permeation module that enhances K⁺ conduction. The GIRK1-selective activator ML297 binds at the GIRK1–GIRK2 interface and controls both permeation and gating. These findings establish how asymmetric assembly couples sequential lipid-dependent gating to efficient K⁺ permeation and GIRK1-dependent pharmacological activation.