title: High constitutive activity is an intrinsic feature of ghrelin receptor protein: a study with a functional monomeric GHS-R1a receptor reconstituted in lipid discs.
abstract: Despite its central role in signaling and the potential therapeutic applications of inverse agonists, the molecular mechanisms underlying G protein-coupled receptor (GPCR) constitutive activity remain largely to be explored. In this context, ghrelin receptor GHS-R1a is a peculiar receptor in the sense that it displays a strikingly high, physiologically relevant, constitutive activity. To identify the molecular mechanisms responsible for this high constitutive activity, we have reconstituted a purified GHS-R1a monomer in a lipid disc. Using this reconstituted system, we show that the isolated ghrelin receptor per se activates G(q) in the absence of agonist, as assessed through guanosine 5'-O-(thiotriphosphate) binding experiments. The measured constitutive activity is similar in its extent to that observed in heterologous systems and in vivo. This is the first direct evidence for the high constitutive activity of the ghrelin receptor being an intrinsic property of the protein rather than the result of influence of its cellular environment. Moreover, we show that the isolated receptor in lipid discs recruits arrestin-2 in an agonist-dependent manner, whereas it interacts with μ-AP2 in the absence of ligand or in the presence of ghrelin. Of importance, these differences are linked to ligand-specific GHS-R1a conformations, as assessed by intrinsic fluorescence measurements. The distinct ligand requirements for the interaction of purified GHS-R1a with arrestin and AP2 provide a new rationale to the differences in basal and agonist-induced internalization observed in cells.
authors: Institut des Biomolécules Max Mousseron, CNRS UMR 5247, Université de Montpellier 1, Faculté de Pharmacie, 15 avenue Charles Flahaut, BP 14491, 34093 Montpellier cedex 5, France.
authors: Marjorie
authors: M
authors: Damian
authors: Jacky
authors: J
authors: Marie
authors: Jean-Philippe
authors: JP
authors: Leyris
authors: Jean-Alain
authors: JA
authors: Fehrentz
authors: Pascal
authors: P
authors: Verdié
authors: Jean
authors: J
authors: Martinez
authors: Jean-Louis
authors: JL
authors: Banères
authors: Sophie
authors: S
authors: Mary
mesh_terms: D000818:Animals; D019390:Arrestins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D004789:Enzyme Activation; D029941:Fish Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D043802:GTP-Binding Protein alpha Subunits, Gq-G11 / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D016244:Guanosine 5'-O-(3-Thiotriphosphate) / Q000737:chemistry / Q000378:metabolism; D006801:Humans; D008055:Lipids / Q000737:chemistry*; D008565:Membrane Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D008567:Membranes, Artificial; D017434:Protein Structure, Tertiary; D054440:Receptors, Ghrelin / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D049833:Sepia
chemical_list: D019390:Arrestins; D029941:Fish Proteins; D008055:Lipids; D008565:Membrane Proteins; D008567:Membranes, Artificial; D054440:Receptors, Ghrelin; C103903:mu-adaptin-related protein 2; D016244:Guanosine 5'-O-(3-Thiotriphosphate); D043802:GTP-Binding Protein alpha Subunits, Gq-G11