Extracellular ionic locks determine variation in constitutive activity and ligand potency between species orthologs of the free fatty acid receptors FFA2 and FFA3

Hudson, B.D. , Tikhonova, I.G., Pandey, S.K., Ulven, T. and Milligan, G. (2012) Extracellular ionic locks determine variation in constitutive activity and ligand potency between species orthologs of the free fatty acid receptors FFA2 and FFA3. Journal of Biological Chemistry, 287(49), pp. 41195-41209. (doi: 10.1074/jbc.M112.396259)

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Abstract

Free fatty acid receptors 2 and 3 (FFA2 and FFA3) are G protein-coupled receptors for short chain free fatty acids (SCFAs). They respond to the same set of endogenous ligands but with distinct rank-order of potency, such that acetate (C2) has been described as FFA2 selective while propionate (C3) is non-selective. Although C2 was confirmed to be selective for human FFA2 over FFA3, this ligand was not selective between the mouse orthologs. Moreover, although C3 was indeed not selective between the human orthologs it displayed clear selectivity for mouse FFA3 over mouse FFA2. This altered selectivity to C2 and C3 resulted from broad differences in SCFAs potency at the mouse orthologs. In studies to define the molecular basis for these observations marked variation in ligand-independent, constitutive activity was identified. The orthologs with higher potency for the SCFAs, human FFA2 and mouse FFA3, displayed high constitutive activity while the orthologs with lower potency for the agonist ligands, mouse FFA2 and human FFA3, did not. Sequence alignments of the 2nd extracellular loop identified single negatively charged residues in FFA2 and FFA3 not conserved between species and predicted to form ‘ionic lock’ interactions with arginine residues within the FFA2 or FFA3 agonist binding pocket to regulate constitutive activity and SCFA potency. Reciprocal mutation of these residues between species orthologs resulted in the induction (or repression) of constitutive activity, and in most cases also yielded corresponding changes in SCFA pote

Item Type:Articles
Status:Published
Refereed:Yes
Glasgow Author(s) Enlighten ID:Hudson, Dr Brian and Milligan, Professor Graeme
Authors: Hudson, B.D., Tikhonova, I.G., Pandey, S.K., Ulven, T., and Milligan, G.
College/School:College of Medical Veterinary and Life Sciences > Institute of Molecular Cell and Systems Biology
Journal Name:Journal of Biological Chemistry
Journal Abbr.:J Biol Chem.
Publisher:American Society for Biochemistry and Molecular Biology, Inc.
ISSN:0021-9258
ISSN (Online):1083-351X
Published Online:12 October 2012

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Project CodeAward NoProject NamePrincipal InvestigatorFunder's NameFunder RefLead Dept
519861Developing selective ligands for Free Fatty Acid Receptor 2 with novel pharmacological propertiesGraeme MilliganWellcome Trust (WELLCOME)089600/Z/09/ZRI NEUROSCIENCE & PSYCHOLOGY