The G Protein-Coupling Profile of Metabotropic Glutamate Receptors, as Determined with Exogenous G Proteins, Is Independent of Their Ligand Recognition Domain
- Marie-Laure Parmentier1,
- Cécile Joly,
- Sophie Restituito,
- Joël Bockaert,
- Yves Grau and
- Jean-Philippe Pin
- Mécanismes Moléculaires des Communications Cellulaires, UPR-9023 Centre National de la Recherche Scientifique, Institute National de la Santé et de la Recherche Médicale de Pharmacologie/Endocrinologie, 34094 Montpellier Cedex 05, France
Abstract
Metabotropic glutamate (mGlu), Ca2+-sensing, γ-aminobutyric acidB, and a large number of pheromone receptors constitute a peculiar family of G protein-coupled receptors. They possess a large extracellular domain that has been proposed to constitute their ligand binding domain. The aim of the current study was to examine whether this large ligand binding domain had any influence on the G protein-coupling selectivity of the receptor, and vice versa. We chose mGlu receptors, which are classified into three groups according to their sequence homology and pharmacology, as representatives of this receptor family. To define a G protein-coupling profile for these receptors, we used a set of exogenous phospholipase C-activating G proteins in the same way that synthetic ligands are used to define agonist and antagonist pharmacological profiles. This set includes Gα15, Gα16, Gαq, and chimeric Gαq proteins with the last few amino acids of either Gαi2 (Gαqi), Gαo(Gαqo), or Gαz (Gαqz). Cotransfection of mGlu receptors with these G proteins and examination of their coupling to phospholipase C revealed that group I, II, and III receptors have distinct G protein-coupling profiles. By swapping the extracellular domains of the most distantly related mGlu receptors (the rat group I mGlu1a and the Drosophila melanogaster group II DmGluA receptors), we show that the extracellular domain determines the agonist pharmacological profile and that this domain does not modify the G protein-coupling profile determined by the seven-transmembrane-domain region of mGlu receptors.
Footnotes
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Send reprint requests to: Dr. J.-P. Pin, CCIPE, 141 rue de la Cardonille, 34094 Montpellier, Cedex 5, France. E-mail:pin{at}ccipe.montp.inserm.fr
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↵1 Current affiliation: Department of Genetics, University of Cambridge, Cambridge CB2 3EH, UK.
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This work was supported by grants from the Centre Nationale de Recherche Scientifique, the European Community [Biomed2 (BMH4-CT96–0228) and Biotech2 (BIO4-CT96–0049) Programs], the French Ministry of Education, Research and Professional Insertion (ACC-SV5, Grant 9505077), the Fondation pour la Recherche Médicale, the Direction des Recherches et Etudes Techniques (DRET 91/161). and Bayer (France and Germany).
- Abbreviations:
- GPCR
- G protein-coupled receptor
- ACPD
- 1-amino-1,3-cyclopentane-dicarboxylate
- ACPT-I
- (1S,3R,4S)-1-aminocyclopentane-1,3,4-tricarboxylic acid
- DL-AP4
- dl-2-amino-4-phosphonobutanoate
- APDC
- 4-aminopyrrolidine-2,4-dicarboxylate
- L-CCGI
- (2S,3S,4S)-α-(carboxycyclopropyl)glycine
- DMEM
- Dulbecco’s modified Eagle’s medium
- DHPG
- (RS)-3,5-dihydroxyphenylglycine
- DCG IV
- (2S,1′R,2′R,3′R)-2-(2,3-dicarboxycyclopropyl)glycine
- IP
- inositol phosphate
- HEK
- human embryonic kidney
- LH
- luteinizing hormone
- mGlu
- metabotropic glutamate
- PBP
- periplasmic binding protein
- PLC
- phospholipase C
- L-SOP
- l-serine-O-phosphate
- 7TM
- seven transmembrane domain
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- Received October 2, 1997.
- Accepted January 2, 1998.
- The American Society for Pharmacology and Experimental Therapeutics
