Extracellular Loop 2 of the Free Fatty Acid Receptor 2 Mediates Allosterism of a Phenylacetamide Ago-Allosteric Modulator

Nicola J. Smith, Richard J. Ward, Leigh A. Stoddart, Brian D. Hudson, Evi Kostenis, Trond Ulven, Joanne C. Morris, Christian Trankle, Irina G. Tikhonova, David R. Adams, Graeme Milligan

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57 Citations (Scopus)


Allosteric agonists are powerful tools for exploring the pharmacology of closely related G protein-coupled receptors that have nonselective endogenous ligands, such as the short chain fatty acids at free fatty acid receptors 2 and 3 (FFA2/GPR43 and FFA3/GPR41, respectively). We explored the molecular mechanisms mediating the activity of 4-chloro-alpha-(1-methylethyl)-N-2-thiazolylbenzeneacetamide (4-CMTB), a recently described phenylacetamide allosteric agonist and allosteric modulator of endogenous ligand function at human FFA2, by combining our previous knowledge of the orthosteric binding site with targeted examination of 4-CMTB structure-activity relationships and mutagenesis and chimeric receptor generation. Here we show that 4-CMTB is a selective agonist for FFA2 that binds to a site distinct from the orthosteric site of the receptor. Ligand structure-activity relationship studies indicated that the N-thiazolyl amide is likely to provide hydrogen bond donor/acceptor interactions with the receptor. Substitution at Leu(173) or the exchange of the entire extracellular loop 2 of FFA2 with that of FFA3 was sufficient to reduce or ablate, respectively, allosteric communication between the endogenous and allosteric agonists. Thus, we conclude that extracellular loop 2 of human FFA2 is required for transduction of cooperative signaling between the orthosteric and an as-yet-undefined allosteric binding site of the FFA2 receptor that is occupied by 4-CMTB.

Original languageEnglish
Pages (from-to)163-173
Number of pages11
JournalMolecular Pharmacology
Issue number1
Early online date15 Apr 2011
Publication statusPublished - 01 Jul 2011

ASJC Scopus subject areas

  • Pharmacology
  • Molecular Medicine


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