Cryo-EM analysis of PIP2 regulation in mammalian GIRK channels
Yiming Niu, Xiao Tao, Kouki K Touhara, Roderick MacKinnon
Abstract
G-protein-gated inward rectifier potassium (GIRK) channels are regulated by G proteins and PIP 2 . Here, using cryo-EM single particle analysis we describe the equilibrium ensemble of structures of neuronal GIRK2 as a function of the C8-PIP 2 concentration. We find that PIP 2 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, PIP 2 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 PIP 2 influences GIRK channels in a structurally similar manner to Kir2.2 channels. In Kir2.2 channels, the PIP 2 -induced conformational changes open the pore. In GIRK channels, they prepare the channel for activation by G βγ .