Distinct subdomains of human endothelin receptors determine their selectivity to endothelinA-selective antagonist and endothelinB-selective agonists

Aiji Sakamoto, Masashi Yanagisawa, Tatsuya Sawamura, Taijiro Enoki, Toshio Ohtani, Takeshi Sakurai, Kazuwa Nakao, Teruhiko Toyo-oka, Tomoh Masaki

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Abstract

The endothelin (ET) family of peptides acts via two subtypes of G-protein-coupled heptahelical receptors termed ETA and ETB, which have distinct rank orders of affinity to endothelin receptor agonists and antagonists. To delineate which portions of the receptor molecules determine ligand selectivity, we have constructed a series of chimeras between human ETA and ETB receptors and characterized the chimeric receptors expressed in heterologous cell lines by competitive radioligand binding analysis and by measuring agonist-induced transients of intracellular Ca2+. We demonstrate that the binding determinant for the ETB-selective agonists ET-3, BQ3020, and IRL1620 resides within the region spanning the putative transmembrane helices IV-VI and the adjacent loop regions. In contrast, the transmembrane helices I, II, III, and VII plus the intervening loop regions specify the selectivity for BQ123, an ETA-selective antagonist. BQ123 exhibited no detectable agonistic activity in all wild-type and chimeric receptors tested. A chimeric receptor that has the transmembrane helices IV-VI (and adjacent loops) from the ETB receptor inserted into the remaining regions from the ETA receptor binds both the ETA-and ETB-selective ligands with high affinities. Moreover, BQ123 competitively inhibits the binding of the amino-terminally truncated ETB agonists, 125I-BQ3020 and 125I-IRL1620, to this chimeric receptor, suggesting that BQ123 is a mimic of the carboxyl-terminal linear portion of endothelins. These findings indicate that there are at least two separable ligand interaction subdomains within the endothelin receptors.

Original languageEnglish (US)
Pages (from-to)8547-8553
Number of pages7
JournalJournal of Biological Chemistry
Volume268
Issue number12
Publication statusPublished - Apr 25 1993

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ASJC Scopus subject areas

  • Biochemistry

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