Palmitoylation of the KATP channel Kir6.2 subunit promotes channel opening by regulating PIP2 sensitivity

A physiological role for long-chain acyl-CoA esters to activate ATP-sensitive K+ (K-ATP) channels is well established. Circulating palmitate is transported into cells and converted to palmitoyl-CoA, which is a substrate for palmitoylation. We found that palmitoyl-CoA, but not palmitic acid, activated the channel when applied acutely. We have altered the palmitoylation state by preincubating cells with micromolar concentrations of palmitic acid or by inhibiting protein thioesterases. With acyl-biotin exchange assays we found that Kir6.2, but not sulfonylurea receptor (SUR)1 or SUR2, was palmitoylated. These interventions increased the K-ATP channel mean patch current, increased the open time, and decreased the apparent sensitivity to ATP without affecting surface expression. Similar data were obtained in transfected cells, rat insulin-secreting INS-1 cells, and isolated cardiac myocytes. Kir6.2 Delta C36, expressed without SUR, was also positively regulated by palmitoylation. Mutagenesis of Kir6.2 Cys(166) prevented these effects. Clinical variants in KCNJ11 that affect Cys(166) had a similar gain-of-function phenotype, but was more pronounced. Molecular modeling studies suggested that palmitoyl-C-166 and selected large hydrophobic mutations make direct hydrophobic contact with Kir6.2-bound PIP2. Patch-clamp studies confirmed that palmitoylation of Kir6.2 at Cys(166) enhanced the PIP2 sensitivity of the channel. Physiological relevance is suggested since palmitoylation blunted the regulation of KATP channels by alpha 1-adrenoreceptor stimulation. The Cys(166) residue is conserved in some other Kir family members (Kir6.1 and Kir3, but not Kir2), which are also subject to regulated palmitoylation, suggesting a general mechanism to control the open state of certain Kir channels.