Sulphonylurea Receptors Regulate Kir6.2 Subunits Allosterically via a Salt Bridge in Cardiac K ATP Channels

Abstract

ATP sensitive potassium (KATP) channels play important roles in many tissues, coupling metabolic status to membrane potential. In heart, they comprise subunit hetero-octamers of Kir6.24/SUR2A4.A minimal sequence (residues 1294-1358) in nucleotide binding domain-2 of SUR2A has been indentified previously by us to bind Kir6.2 (Rainbow et. al. Biochem. J. 2004;379:173-181). Co-immunoprecipitation of chimaeras of Kir6.2/Kir2.1 with maltose binding protein (MBP)-tagged SUR2A(1294-1358) fragments identified the cognate binding domain in Kir6.2 (residues 315-390). Mutagenesis of charged residues in Kir6.2, D323K and K338E, conserved in Kir6.1 but not Kir2.1, was alone sufficient to significantly reduce co-immunoprecipitation of MBP-SUR2A(1294-1358) by ∼50 % (P 0.5).Together, these data provide evidence for the transmission of allosteric information via a salt bridge between SUR2AE1318 and Kir6.2K338 in cardiac KATP channels, while ATP-sensitivity remains unaltered.