title: Evidence for a single heptahelical domain being turned on upon activation of a dimeric GPCR.
abstract: G-protein-coupled receptors (GPCRs) have been shown to form dimers, but the relevance of this phenomenon in G-protein activation is not known. Among the large GPCR family, metabotropic glutamate (mGlu) receptors are constitutive dimers. Here we examined whether both heptahelical domains (HDs) are turned on upon full receptor activation. To that aim, we measured G-protein coupling efficacy of dimeric mGlu receptors in which one subunit bears specific mutations. We show that a mutation in the third intracellular loop (i3 loop) known to prevent G-protein activation in a single subunit decreases coupling efficacy. However, when a single HD is blocked in its inactive state using an inverse agonist, 2-methyl-6-(phenylethynyl)pyridine (MPEP), no decrease in receptor activity is observed. Interestingly, in a receptor dimer in which the subunit that binds MPEP is mutated in its i3 loop, MPEP enhances agonist-induced activity, reflecting a 'better' activation of the adjacent HD. These data are consistent with a model in which a single HD is turned on upon activation of such homodimeric receptors and raise important issues in deciphering the functional role of GPCR dimer formation for G-protein activation.
authors.affiliation: Department of Molecular Pharmacology, Institute of Experimental Medicine, Czech Academy of Science, Prague, Czech Republic.
authors.forename: Veronika
authors.initials: V
authors.lastname: Hlavackova
authors.forename: Cyril
authors.initials: C
authors.lastname: Goudet
authors.forename: Julie
authors.initials: J
authors.lastname: Kniazeff
authors.forename: Alice
authors.initials: A
authors.lastname: Zikova
authors.forename: Damien
authors.initials: D
authors.lastname: Maurel
authors.forename: Claire
authors.initials: C
authors.lastname: Vol
authors.forename: Johana
authors.initials: J
authors.lastname: Trojanova
authors.forename: Laurent
authors.initials: L
authors.lastname: Prézeau
authors.forename: Jean-Philippe
authors.initials: JP
authors.lastname: Pin
authors.forename: Jaroslav
authors.initials: J
authors.lastname: Blahos
mesh_terms: D002460:Cell Line; D019281:Dimerization; D018691:Excitatory Amino Acid Antagonists / Q000494:pharmacology; D006801:Humans; D066298:In Vitro Techniques; D007700:Kinetics; D008954:Models, Biological; D016297:Mutagenesis, Site-Directed; D017434:Protein Structure, Tertiary; D021122:Protein Subunits; D011725:Pyridines / Q000494:pharmacology; D018094:Receptors, Metabotropic Glutamate / Q000037:antagonists & inhibitors / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D011993:Recombinant Fusion Proteins / Q000037:antagonists & inhibitors / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D011994:Recombinant Proteins / Q000037:antagonists & inhibitors / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D014162:Transfection
chemical_list: D018691:Excitatory Amino Acid Antagonists; D021122:Protein Subunits; D011725:Pyridines; D018094:Receptors, Metabotropic Glutamate; D011993:Recombinant Fusion Proteins; D011994:Recombinant Proteins; C104077:metabotropic glutamate receptor type 1; C121465:6-methyl-2-(phenylethynyl)pyridine