title: Role of the amino-terminal transmembrane domain of sulfonylurea receptor SUR2B for coupling to K(IR)6.2, ligand binding, and oligomerization.
abstract: ATP-sensitive K(+) (K(ATP)) channels consist of two types of subunits, K(IR)6.x that form the pore, and sulfonylurea receptors (SURs) that serve as regulatory subunits. SURs are ATP-binding cassette (ABC) proteins and contain, in addition to two nucleotide binding folds, the binding sites for channel openers such as diazoxide and P1075 and channel inhibitors such as glibenclamide (GBC) and repaglinide. Structurally, SURs differ from most eukaryotic ABC proteins by an additional amino-terminal transmembrane domain (TMD0); in case of SUR1, the subunit of the pancreatic K(ATP) channel, TMD0 serves as a major domain for association with K(IR). In this study we sought to elucidate the roles of TMD0 in SUR2B, the smooth muscle gating subunit, in the coupling between SUR2B and K(IR)6.2, in the self-association of SUR2B and in channel modulator binding to SUR2B. SUR2B has a weaker affinity for sulfonylureas thus SUR2B(Y1206S), with a higher affinity for GBC, but an equivalent opener binding was used. Association of SUR2B(YS)Δ, lacking TMD0, with K(IR)6.2 was shown by immunoprecipitation; however, no evidence for formation of functional channels was obtained. SUR2B(YS)Δ self-associates like SUR2B(YS) and binds GBC, repaglinide, and P1075 with slightly reduced affinities. The binding profile of the SUR2B(YS)Δ/K(IR)6.2 complex differs slightly but significantly from that of SUR2B(YS)Δ alone showing impaired allosteric coupling of binding sites. We conclude that TMD0 is not required for oligomerization of SUR2B, is of only minor importance in ligand binding, but is essential for both functional and allosteric coupling of SUR2B to K(IR)6.2.
authors.affiliation: Department of Pharmacology and Experimental Therapy, Institute of Experimental and Clinical Pharmacology and Toxicology, Eberhard-Karls-University Hospitals and Clinics, Wilhelmstr. 56, 72074, Tübingen, Germany.
authors.forename: Marcus
authors.initials: M
authors.lastname: Winkler
authors.forename: Petra
authors.initials: P
authors.lastname: Kühner
authors.forename: Ulrich
authors.initials: U
authors.lastname: Russ
authors.forename: David
authors.initials: D
authors.lastname: Ortiz
authors.forename: Joseph
authors.initials: J
authors.lastname: Bryan
authors.forename: Ulrich
authors.initials: U
authors.lastname: Quast
mesh_terms: D018528:ATP-Binding Cassette Transporters / Q000737:chemistry* / Q000502:physiology*; D000818:Animals; D001665:Binding Sites; D057809:HEK293 Cells; D006801:Humans; D008024:Ligands; D051379:Mice; D018408:Patch-Clamp Techniques; D024661:Potassium Channels, Inwardly Rectifying / Q000737:chemistry* / Q000502:physiology*; D017434:Protein Structure, Tertiary; D011869:Radioligand Assay; D011955:Receptors, Drug / Q000737:chemistry* / Q000502:physiology*; D064233:Sulfonylurea Receptors; D000099161:Kcnj11 Channel
chemical_list: D018528:ATP-Binding Cassette Transporters; D008024:Ligands; D024661:Potassium Channels, Inwardly Rectifying; D011955:Receptors, Drug; D064233:Sulfonylurea Receptors; D000099161:Kcnj11 Channel; C577507:ABCC8 protein, human; C577508:Abcc8 protein, mouse; C577511:Abcc9 protein, mouse
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