Cryo-EM analysis of PIP₂ regulation in mammalian GIRK channels

G-protein-gated inward rectifier potassium (GIRK) channels are regulated by G proteins and PIP₂. Here, using cryo-EM single particle analysis we describe the equilibrium ensemble of structures of neuronal GIRK2 as a function of the C8-PIP₂ concentration. We find that PIP₂ shifts the equilibrium between two distinguishable structures of neuronal GIRK (GIRK2), extended and docked, towards the docked form. In the docked form the cytoplasmic domain, to which G_βγ binds, becomes accessible to the cytoplasmic membrane surface where G_βγ resides. Furthermore, PIP₂ binding reshapes the G_βγ binding surface on the cytoplasmic domain, preparing it to receive G_βγ. We find that cardiac GIRK (GIRK1/4) can also exist in both extended and docked conformations. These findings lead us to conclude that PIP₂ influences GIRK channels in a structurally similar manner to Kir2.2 channels. In Kir2.2 channels, the PIP₂-induced conformational changes open the pore. In GIRK channels, they prepare the channel for activation by G_βγ.