Dependence of agonist activation on a conserved apolar residue in the third intracellular loop of the AT1 angiotensin receptor

László Hunyady, Meng Zhang, Gowraganahalli Jagadeesh, Márta Bor, Tamás Balla, Kevin J. Catt

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The coupling of agonist-activated seven transmembrane domain receptors to G proteins is known to involve the amino-terminal region of their third cytoplasmic loop. Analysis of the amino acids in this region of the rat type 1a angiotensin (AT(1a)) receptor identified Leu-222 as an essential residue in receptor activation by the physiological agonist, angiotensin II (Ang II). Nonpolar replacements for Leu-222 yielded functionally intact AT1 receptors, while polar or charged residues caused progressive impairment of Ang II- induced inositol phosphate generation. The decrease in agonist-induced signal generation was associated with a parallel reduction of receptor internalization, and was most pronounced for the Lys-222 mutant receptor. Although this mutant showed normal binding of the peptide antagonist, [Sar1,Ile8]Ang II, its affinity for Ang II was markedly reduced, consistent with its inability to adopt the high-affinity conformation. A search revealed that many G(q)-coupled receptors contain an apolar amino acid (frequently leucine) in the position corresponding to Leu-222 of the AT1 receptor. These findings suggest that such a conserved apolar residue in the third intracellular loop is a crucial element in the agonist-induced activation of the AT1 and possibly many other G protein-coupled receptors.

Original languageEnglish
Pages (from-to)10040-10045
Number of pages6
JournalProceedings of the National Academy of Sciences of the United States of America
Issue number19
Publication statusPublished - Sep 17 1996



  • G protein-coupled receptors
  • inositol phosphate signaling
  • receptor internalization
  • site-directed mutagenesis

ASJC Scopus subject areas

  • General

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