The mutation Y1206S increases the affinity of the sulphonylurea receptor SUR2A for glibenclamide and enhances the effects of coexpression with Kir6.2.
1. ATP-sensitive K(+) channels (K(ATP) channels) are tetradimeric complexes of inwardly rectifying K(+) channels (Kir6.x) and sulphonylurea receptors (SURs). The SURs SUR2A (cardiac) and SUR2B (smooth muscle) differ only in the last 42 amino acids. In SUR2B, the mutation Y1206S, located at intracellular loop 8, increases the affinity for glibenclamide (GBC) about 10-fold. Here, we examined whether the mutation Y1206S in SUR2A had effects similar to those in SUR2B.2. GBC bound to SUR2A with K(D)=20 nM; the mutation increased affinity approximately 5 x. 3. In cells, coexpression of SUR2A with Kir6.2 increased the affinity for GBC approximately 3 x; with the mutant, the increase was 9 x. 4. The mutation did not affect the affinity of SUR2A for openers; coexpression with Kir6.2 reduced opener affinity of wild-type and mutant SUR2A by about 2 x. 5. The negative allosteric interaction between the opener, P1075, and GBC at wild-type and mutant SUR2A was markedly affected by the presence of MgATP and by coexpression with Kir6.2. 6. In inside-out patches, GBC inhibited the wild-type Kir6.2/SUR2A and 2B channels with IC(50) values of 27 nM; the mutation shifted the IC(50) values to approximately 1 nM. 7. The data show that the mutation Y1206S increased the affinity of SUR2A for GBC and modulated the effects of coexpression. Overall, the changes were similar to those observed with SUR2B(Y1206S), suggesting that the differences in the last 42 carboxy-terminal amino acids of SUR2A and 2B are of limited influence on the binding of GBC and P1075 to the SUR2 isoforms.
Stephan
Damian
D
Department of Pharmacology and Toxicology, Medical Faculty, Pharmakologisches Institut/Abt. Molekularpharmakologie, University of Tübingen, Wilhelmstr. 56, Tübingen, D-72074 Germany.
Stauss
Eva
E
Lange
Ulf
U
Felsch
Holger
H
Löffler-Walz
Cornelia
C
Hambrock
Annette
A
Russ
Ulrich
U
Quast
Ulrich
U
D018528:ATP-Binding Cassette Transporters / Q000096:biosynthesis / Q000235:genetics* / Q000378:metabolism*; D000818:Animals; D004305:Dose-Response Relationship, Drug; D005905:Glyburide / Q000378:metabolism*; D051379:Mice; D009154:Mutation; D015221:Potassium Channels / Q000096:biosynthesis / Q000235:genetics* / Q000378:metabolism*; D024661:Potassium Channels, Inwardly Rectifying / Q000096:biosynthesis* / Q000235:genetics* / Q000378:metabolism*; D011485:Protein Binding / Q000235:genetics; D011955:Receptors, Drug / Q000096:biosynthesis / Q000235:genetics* / Q000378:metabolism*; D012694:Serine / Q000235:genetics*; D064233:Sulfonylurea Receptors; D014443:Tyrosine / Q000235:genetics*; D000099161:Kcnj11 Channel
D018528:ATP-Binding Cassette Transporters; D005905:Glyburide; D015221:Potassium Channels; D024661:Potassium Channels, Inwardly Rectifying; D011955:Receptors, Drug; D012694:Serine; D064233:Sulfonylurea Receptors; D014443:Tyrosine; D000099161:Kcnj11 Channel; C577511:Abcc9 protein, mouse