The dynamic interplay of PIP 2 and ATP in the regulation of the K ATP channel.

ATP-sensitive potassium (K ATP ) channels couple the intracellular ATP concentration to insulin secretion. K ATP channel activity is inhibited by ATP binding to the Kir6.2 tetramer and activated by phosphatidylinositol 4,5-bisphosphate (PIP 2 ). Here, we use molecular dynamics simulation, electrophysiology and fluorescence spectroscopy to show that ATP and PIP 2 occupy different binding pockets that share a single amino acid residue, K39. When both ligands are present, simulations suggest that K39 shows a greater preference to co-ordinate with PIP 2 than with ATP. They also predict that a neonatal diabetes mutation at K39 (K39R) increases the number of hydrogen bonds formed between K39 and PIP 2 , potentially accounting for the reduced ATP inhibition observed in electrophysiological experiments. Our work suggests that PIP 2 and ATP interact allosterically to regulate K ATP channel activity. KEY POINTS: The K ATP channel is activated by the binding of phosphatidylinositol 4,5-bisphosphate (PIP 2 ) lipids and inactivated by the binding of ATP. K39 has the potential to bind to both PIP 2 and ATP. A mutation to this residue (K39R) results in neonatal diabetes. This study uses patch-clamp fluorometry, electrophysiology and molecular dynamics simulation. We show that PIP 2 competes with ATP for K39, and this reduces channel inhibition by ATP. We show that K39R increases channel affinity to PIP 2 by increasing the number of hydrogen bonds with PIP 2 , when compared with the wild-type K39. This therefore decreases K ATP channel inhibition by ATP.