Truncation of Kir6.2 produces ATP-sensitive K+ channels in the absence of the sulphonylurea receptor

Abstract

ATP-sensitive potassium channels (K-ATP channels) couple cell metabolism to electrical activity and are important in the physiology and pathophysiology of many tissues. In pancreatic beta-cells, K-ATP channels link changes in blood glucose concentration to insulin secretion. They are also the target for clinically important drugs such as sulphonylureas, which stimulate secretion, and the K+ channel opener diazoxide, which inhibits insulin release. Metabolic regulation of K-ATP channels is mediated by changes in intracellular ATP and Mg-ADP levels, which inhibit and activate the channel, respectively. The beta-cell K-ATP channel is a complex of two proteins: an inward-rectifier K+ channel subunit, Kir6.2, and the sulphonylurea receptor, SUR1. We show here that the primary site at which ATP acts to mediate K-ATP channel inhibition is located on Kir6.2, and that SUR1 is required for sensitivity to sulphonylureas and diazoxide and for activation by Mg-ADP.

ATP-sensitive K channel channel/enzyme multimer: Metabolic gating in the heart

“…Assembly of Kir6.2 with SUR enhances ATP-induced inhibition of the channel pore [25], and defines the tissue-specific burst kinetics of K ATP channel behavior [5,34,35]. Furthermore, fundamental K ATP channel properties, including stimulation by MgADP and potassium channel openers as well as inhibition by sulfonylurea drugs that are absent in truncated Kir6.2 channels, are rescued by co-expression of Kir6.2 with SUR [25,36].…”

“…The poreforming Kir6.2 subunits cannot readily traffic to the plasma membrane alone, without the regulatory SUR module, due to a C-terminal RKR endoplasmic reticulum retention signal [23,24]. When engineered to be expressed independently of SUR through truncation of the Cterminal amino acids, the Kir6.2 subunit was identified as critical for K ATP channel inhibition by intracellular ATP [25,26]. Although a conventional nucleotide binding motif has not been identified within the Kir6.2 sequence, photoaffinity labeling and scanning with sulfhydryl group reagents accomplished by mutagenesis identified that both N-and C-termini may contribute to recognition of ATP [27,28,29].…”

“…Furthermore, fundamental K ATP channel properties, including stimulation by MgADP and potassium channel openers as well as inhibition by sulfonylurea drugs that are absent in truncated Kir6.2 channels, are rescued by co-expression of Kir6.2 with SUR [25,36].…”

“…Indeed, the classical allosteric model was successfully applied to nucleotidedependent K ATP channel gating [15] which presumed that four identical binding sites for ATP and ADP co-exist within the octameric stoichiometry of the K ATP channel complex [22]; binding of ATP to the pore-forming Kir6.2 subunit inhibits channel opening [25,26], whereas binding of ADP to the corresponding regulatory SUR subunit antagonizes ATP-binding to Kir6.2 [43,81]. Although this classic allosteric model of channel regulation was in agreement with experimentally defined nucleotide-dependent gating (i.e.…”

Nucleotide-gated KATPchannels integrated with creatine and adenylate kinases: Amplification, tuning and sensing of energetic signals in the compartmentalized cellular environment

“…1) [13][14][15]. ATP maintains K ATP channel closure by binding to Kir6.2 [16,17], whereas ATP/ADP interactions with SUR secure the metabolic sensor function of the channel complex (Fig. 1A) [18][19][20].…”