Identification of the PIP₂-binding site on Kir6.2 by molecular modelling and functional analysis

ATP-sensitive potassium (K_ATP) channels couple cell metabolism to electrical activity by regulating K⁺ fluxes across the plasma membrane. Channel closure is facilitated by ATP, which binds to the pore-forming subunit (Kir6.2). Conversely, channel opening is potentiated by phosphoinositol bisphosphate (PIP₂), which binds to Kir6.2 and reduces channel inhibition by ATP. Here, we use homology modelling and ligand docking to identify the PIP₂-binding site on Kir6.2. The model is consistent with a large amount of functional data and was further tested by mutagenesis. The fatty acyl tails of PIP₂ lie within the membrane and the head group extends downwards to interact with residues in the N terminus (K39, N41, R54), transmembrane domains (K67) and C terminus (R176, R177, E179, R301) of Kir6.2. Our model suggests how PIP₂ increases channel opening and decreases ATP binding and channel inhibition. It is likely to be applicable to the PIP₂-binding site of other Kir channels, as the residues identified are conserved and influence PIP₂ sensitivity in other Kir channel family members.