RT Journal Article
SR Electronic
T1 Testing the Bipartite Model of the Sulfonylurea Receptor Binding Site: Binding of A-, B-, and A + B-Site Ligands
JF Journal of Pharmacology and Experimental Therapeutics
JO J Pharmacol Exp Ther
FD American Society for Pharmacology and Experimental Therapeutics
SP 701
OP 708
DO 10.1124/jpet.107.123224
VO 322
IS 2
A1 Marcus Winkler
A1 Damian Stephan
A1 Susanne Bieger
A1 Petra Kühner
A1 Felix Wolff
A1 Ulrich Quast
YR 2007
UL http://jpet.aspetjournals.org/content/322/2/701.abstract
AB ATP-sensitive K+ (KATP) channels are composed of pore-forming subunits (Kir6.x) and of regulatory subunits, the sulfonylurea receptors (SURx). Subtypes of KATP channels are expressed in different organs. The sulfonylureas and glinides (insulinotropes) close the KATP channel in pancreatic β-cells and stimulate insulin secretion. The insulinotrope binding site of the pancreatic channel (Kir6.2/SUR1) consists of two overlapping (sub)-sites, site A, located on SUR1 and containing Ser1237 (which in SUR2 is replaced by Tyr1206), and site B, formed by SUR1 and Kir6.2. Insulinotropes bind to the A-, B-, or A + B-site(s) and are grouped accordingly. A-ligands are highly selective in closing the pancreatic channel, whereas B-ligands are nonselective and insensitive to the mutation S1237Y. We have examined the binding of insulinotropes representative of the three groups in [3H]glibenclamide competition experiments to determine the contribution of Kir6.x to binding affinity, the effect of the mutation Y1206S in site A of SUR2, and the subtype selectivity of the compounds. The results show that the bipartite nature of the SUR1 binding site applies also to SUR2. Kir6.2 as part of the B-site may interact directly or allosterically with structural elements common to all insulinotropes, i.e., the negative charge and/or the adjacent phenyl ring. The B-site confers a moderate subtype selectivity on B-ligands. The affinity of B-ligands is altered by the mutation SUR2(Y1206S), suggesting that the mutation affects the binding chamber of SUR2 as a whole or subsite A, including the region where the subsites overlap. The American Society for Pharmacology and Experimental Therapeutics