The ATPase activities of sulfonylurea receptor 2A and sulfonylurea receptor 2B are influenced by the C-terminal 42 amino acids.
Unusually among ATP-binding cassette proteins, the sulfonylurea receptor (SUR) acts as a channel regulator. ATP-sensitive potassium channels are octameric complexes composed of four pore-forming Kir6.2 subunits and four regulatory SUR subunits. Two different genes encode SUR1 (ABCC8) and SUR2 (ABCC9), with the latter being differentially spliced to give SUR2A and SUR2B, which differ only in their C-terminal 42 amino acids. ATP-sensitive potassium channels containing these different SUR2 isoforms are differentially modulated by MgATP, with Kir6.2/SUR2B being activated more than Kir6.2/SUR2A. We show here that purified SUR2B has a lower ATPase activity and a 10-fold lower K(m) for MgATP than SUR2A. Similarly, the isolated nucleotide-binding domain (NBD) 2 of SUR2B was less active than that of SUR2A. We further found that the NBDs of SUR2B interact, and that the activity of full-length SUR cannot be predicted from that of either the isolated NBDs or NBD mixtures. Notably, deletion of the last 42 amino acids from NBD2 of SUR2 resulted in ATPase activity resembling that of NBD2 of SUR2A rather than that of NBD2 of SUR2B: this might indicate that these amino acids are responsible for the lower ATPase activity of SUR2B and the isolated NBD2 of SUR2B. We suggest that the lower ATPase activity of SUR2B may result in enhanced duration of the MgADP-bound state, leading to channel activation.
de Wet
Heidi
H
Department of Physiology, Anatomy and Genetics, University of Oxford, UK.
Fotinou
Constantina
C
Amad
Nawaz
N
Dreger
Matthias
M
Ashcroft
Frances M
FM
D018528:ATP-Binding Cassette Transporters / Q000378:metabolism*; D000244:Adenosine Diphosphate / Q000378:metabolism / Q000494:pharmacology; D000251:Adenosine Triphosphatases / Q000037:antagonists & inhibitors / Q000378:metabolism*; D000595:Amino Acid Sequence; D000818:Animals; D001608:Beryllium / Q000494:pharmacology; D005459:Fluorides / Q000494:pharmacology; D024661:Potassium Channels, Inwardly Rectifying / Q000378:metabolism*; D051381:Rats; D011955:Receptors, Drug / Q000378:metabolism*; D011993:Recombinant Fusion Proteins / Q000302:isolation & purification / Q000378:metabolism; D064233:Sulfonylurea Receptors
D018528:ATP-Binding Cassette Transporters; C577509:Abcc8 protein, rat; C577512:Abcc9 protein, rat; D024661:Potassium Channels, Inwardly Rectifying; D011955:Receptors, Drug; D011993:Recombinant Fusion Proteins; D064233:Sulfonylurea Receptors; C035982:beryllium fluoride; D000244:Adenosine Diphosphate; D000251:Adenosine Triphosphatases; D001608:Beryllium; D005459:Fluorides