SUR-dependent modulation of KATP channels by an N-terminal KIR6.2 peptide. Defining intersubunit gating interactions.
Ntp and Ctp, synthetic peptides based on the N- and C-terminal sequences of K(IR)6.0, respectively, were used to probe gating of K(IR)6.0/SUR K(ATP) channels. Micromolar Ntp dose-dependently increased the mean open channel probability in ligand-free solution (P(O(max))) and attenuated the ATP inhibition of K(IR)6.2/SUR1, but had no effect on homomeric K(IR)6.2 channels. Ntp (up to approximately 10(-4) m) did not affect significantly the mean open or "fast," K(+) driving force-dependent, intraburst closed times, verifying that Ntp selectively modulates the ratio of mean burst to interburst times. Ctp and Rnp, a randomized Ntp, had no effect, indicating that the effects of Ntp are structure specific. Ntp opened K(IR)6.1/SUR1 channels normally silent in the absence of stimulatory Mg(-) nucleotide(s) and attenuated the coupling of high-affinity sulfonylurea binding with K(ATP) pore closure. These effects resemble those seen with N-terminal deletions (DeltaN) of K(IR)6.0, and application of Ntp to DeltaNK(ATP) channels decreased their P(O(max)) and apparent IC(50) for ATP in the absence of Mg(2+). The results are consistent with a competition between Ntp and the endogenous N terminus for a site of interaction on the cytoplasmic face of the channel or with partial replacement of the deleted N terminus by Ntp, respectively. The K(IR) N terminus and the TMD0-L0 segment of SUR1 are known to control the P(O(max)). The L0 linker has been reported to be required for glibenclamide binding, and DeltaNK(IR)6.2/SUR1 channels exhibit reduced labeling of K(IR) with (125)I-azidoglibenclamide, implying that the K(IR) N terminus and L0 of SUR1 are in proximity. We hypothesize that L0 interacts with the K(IR) N terminus in ligand-inhibited K(ATP) channels and put forward a model, based on the architecture of BtuCD, MsbA, and the KcsA channel, in which TMD0-L0 links the MDR-like core of SUR with the K(IR) pore.
Babenko
Andrey P
AP
Department of Molecular and Cellular Biology, Baylor College of Medicine, Houston, Texas 77030, USA. ababenko@bcm.tmc.edu
Bryan
Joseph
J
D018528:ATP-Binding Cassette Transporters; D000255:Adenosine Triphosphate / Q000494:pharmacology; D000818:Animals; D019556:COS Cells; D003593:Cytoplasm / Q000378:metabolism; D018076:DNA, Complementary / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D004594:Electrophysiology; D017353:Gene Deletion; D007700:Kinetics; D008024:Ligands; D008954:Models, Biological; D018408:Patch-Clamp Techniques; D010455:Peptides / Q000737:chemistry; D015221:Potassium Channels / Q000378:metabolism*; D024661:Potassium Channels, Inwardly Rectifying / Q000378:metabolism*; D011485:Protein Binding; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D011955:Receptors, Drug; D064233:Sulfonylurea Receptors; D013997:Time Factors
D018528:ATP-Binding Cassette Transporters; D018076:DNA, Complementary; D008024:Ligands; D010455:Peptides; D015221:Potassium Channels; D024661:Potassium Channels, Inwardly Rectifying; D011955:Receptors, Drug; D064233:Sulfonylurea Receptors; D000255:Adenosine Triphosphate