Effect of Two Amino Acids in TM17 of Sulfonylurea Receptor SUR1 on the Binding of ATP-Sensitive K+ Channel Modulators

  1. Annette Hambrock,
  2. Tülay Kayar,
  3. Demet Stumpp and
  4. Hartmut Osswald
  1. Department of Pharmacology and Toxicology, Medical Faculty, University of Tübingen, Tübingen, Germany
  1. Address correspondence and reprint requests to Annette Hambrock, Department of Pharmacology and Toxicology, Medical Faculty, University of Tübingen, Wilhelmstraße 56, D-72074 Tübingen, Germany. E-mail: annette.hambrock{at}uni-tuebingen.de

Abstract

The sulfonylurea receptor (SUR) is the important regulatory subunit of ATP-sensitive K+ channels. It is an ATP-binding cassette protein comprising 17 transmembrane helices. SUR is endowed with binding sites for channel blockers like the antidiabetic sulfonylurea glibenclamide and for the chemically very heterogeneous channel openers. SUR1, the typical pancreatic SUR isoform, shows much higher affinity for glibenclamide but considerably lower affinity for most openers than SUR2. In radioligand binding assays, we investigated the role of two amino acids, T1285 and M1289, located in transmembrane helix (TM)-17, in opener binding to SUR1. These amino acids were exchanged for the corresponding amino acids of SUR2. In competition experiments using [3H]glibenclamide as radioligand, SUR1(T1285L, M1289T) showed much higher affinity toward the cyanoguanidine openers pinacidil and P1075 than SUR1 wild type. The affinity for the thioformamide aprikalim was also markedly increased. In contrast, the affinity for the benzopyrans rilmakalim and levcromakalim was unaffected; however, the amount of displaced [3H]glibenclamide binding was nearly doubled. The binding properties of the opener diazoxide and the blocker glibenclamide were unchanged. In conclusion, mutation of two amino acids in TM17 of SUR1, especially of M1289, leads to class-specific effects on opener binding by increasing opener affinity or by changing allosteric coupling between opener and glibenclamide binding.

Footnotes

  • This article is based on a presentation at a symposium. The symposium and the publication of this article were made possible by an unrestricted educational grant from Servier.

    • Accepted May 12, 2004.
    • Received March 12, 2004.
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