Dynamic Role of the Tether Helix in PIP-dependent Gating of a G Protein-gated Potassium Channel

G protein-gated inwardly rectifying potassium (GIRK) channels control neuronal excitability in the brain and are implicated in several different neurological diseases. The anionic phospholipid phosphatidylinositol 4,5 bisphosphate (PIP) is an essential cofactor for GIRK channel gating, but the precise mechanism by which PIP opens GIRK channels remains poorly understood. Previous structural studies have revealed several highly conserved, positively charged residues in the "tether helix" (C-linker) that interact with the negatively charged PIP However, these crystal structures of neuronal GIRK channels in complex with PIP provide only snapshots of PIP's interaction with the channel and thus lack details about the gating transitions triggered by PIP binding. Here, our functional studies reveal that one of these conserved basic residues in GIRK2, Lys200 (6'K), supports a complex and dynamic interaction with PIP When Lys200 is mutated to an uncharged amino acid, it activates the channel by enhancing the interaction with PIP Atomistic molecular dynamic simulations of neuronal GIRK2 with the same 6' substitution reveal an open GIRK2 channel with PIP molecules adopting novel positions. This dynamic interaction with PIP may explain the intrinsic low open probability of GIRK channels and the mechanism underlying activation by G protein Gβγ subunits and ethanol.