Mechanism of action of a sulphonylurea receptor SUR1 mutation (F132L) that causes DEND syndrome

Activating mutations in the genes encoding the ATP-sensitive potassium (K-ATP) channel subunits Kir6.2 and SUR1 are a common cause of neonatal diabetes. Here, we analyse the molecular mechanism of action of the heterozygous mutation F132L, which lies in the first set of transmembrane helices (TMD0) of SUR1. This mutation causes severe developmental delay, epilepsy and permanent neonatal diabetes (DEND syndrome). We show that the F132L mutation reduces the ATP sensitivity of K-ATP channels indirectly, by altering the intrinsic gating of the channel. Thus, the open probability is markedly increased when Kir6.2 is co-expressed with mutant TMD0 alone or with mutant SUR1. The F132L mutation disrupts the physical interaction between Kir6.2 and TMD0, but does not alter the plasmalemma channel density. Our results explain how a mutation in an accessory subunit can produce enhanced activity of the K-ATP channel pore (formed by Kir6.2). They also provide further evidence that interactions between TMD0 of SUR1 and Kir6.2 are critical for K-ATP channel gating and identify a residue crucial for this interaction at both physical and functional levels.