Tandem function of nucleotide binding domains confers competence to sulfonylurea receptor in gating ATP-sensitive K+ channels.
Fundamental to the metabolic sensor function of ATP-sensitive K(+) (K(ATP)) channels is the sulfonylurea receptor. This ATP-binding cassette protein, which contains nucleotide binding domains (NBD1 and NBD2) with conserved Walker motifs, regulates the ATP sensitivity of the pore-forming Kir6.2 subunit. Although NBD2 hydrolyzes ATP, a property essential in K(ATP) channel gating, the role of NBD1, which has limited catalytic activity, if at all, remains less understood. Here, we provide functional evidence that cooperative interaction, rather than the independent contribution of each NBD, is critical for K(ATP) channel regulation. Gating of cardiac K(ATP) channels by distinct conformations in the NBD2 ATPase cycle, induced by gamma-phosphate analogs, was disrupted by point mutation not only of the Walker motif in NBD2 but also in NBD1. Cooling membrane patches to decelerate the intrinsic ATPase activity counteracted ATP-induced K(ATP) channel inhibition, an effect that mimicked stabilization of the MgADP-bound posthydrolytic state at NBD2 by the gamma-phosphate analog orthovanadate. Temperature-induced channel activation was abolished by mutations that either prevent stabilization of MgADP at NBD2 or ATP at NBD1. These findings provide a paradigm of K(ATP) channel gating based on integration of both NBDs into a functional unit within the multimeric channel complex.
Zingman
Leonid V
LV
Division of Cardiovascular Diseases, Department of Medicine, Mayo Clinic, Mayo Foundation, Rochester, Minnesota 55905, USA.
Hodgson
Denice M
DM
Bienengraeber
Martin
M
Karger
Amy B
AB
Kathmann
Eva C
EC
Alekseev
Alexey E
AE
Terzic
Andre
A
D018528:ATP-Binding Cassette Transporters; D000244:Adenosine Diphosphate / Q000378:metabolism; D000255:Adenosine Triphosphate / Q000378:metabolism*; D020816:Amino Acid Motifs; D000818:Animals; D019556:COS Cells; D002462:Cell Membrane / Q000378:metabolism; D006224:Cricetinae; D004247:DNA / Q000378:metabolism*; D004305:Dose-Response Relationship, Drug; D004594:Electrophysiology; D004926:Escherichia coli / Q000378:metabolism; D006168:Guinea Pigs; D008954:Models, Biological; D016297:Mutagenesis, Site-Directed; D009206:Myocardium / Q000378:metabolism; D017354:Point Mutation; D015221:Potassium Channels / Q000737:chemistry* / Q000378:metabolism*; D024661:Potassium Channels, Inwardly Rectifying / Q000378:metabolism; D011485:Protein Binding; D011487:Protein Conformation; D017434:Protein Structure, Tertiary; D011955:Receptors, Drug / Q000737:chemistry*; D011994:Recombinant Proteins / Q000378:metabolism; D064233:Sulfonylurea Receptors; D013997:Time Factors; D014162:Transfection
D018528:ATP-Binding Cassette Transporters; D015221:Potassium Channels; D024661:Potassium Channels, Inwardly Rectifying; D011955:Receptors, Drug; D011994:Recombinant Proteins; D064233:Sulfonylurea Receptors; D000244:Adenosine Diphosphate; D000255:Adenosine Triphosphate; D004247:DNA