title: G protein activation by the leukotriene B4 receptor dimer. Evidence for an absence of trans-activation.
abstract: There is compelling evidence that G protein-coupled receptors exist as homo- and heterodimers, but the way these assemblies function at the molecular level remains unclear. We used here the purified leukotriene B(4) receptor BLT1 stabilized in its dimeric state to analyze how a receptor dimer activates G proteins. For this, we produced heterodimers between the wild-type BLT1 and a BLT1/ALXR chimera. The latter is no longer activated by leukotriene B(4) but is still activated by ALXR agonists. In this heterodimer, agonist binding to either one of the two protomers induced asymmetric conformational changes within the receptor dimer. Of importance, no G protein activation was observed when using a dimer where the ligand-loaded protomer was not able to trigger GDP/GTP exchange due to specific mutations in its third intracellular loop, establishing that the conformation of the agonist-free protomer is not competent for G protein activation. Taken together, these data indicate that although ligand binding to one protomer in the heterodimer is associated with cross-conformational changes, a trans-activation mechanism where the ligand-free subunit would trigger GDP/GTP exchange cannot be considered in this case for G protein activation. This observation sheds light into the way GPCR dimers, in particular heterodimers, could activate their cognate G proteins.
authors.affiliation: Institut des Biomolécules Max Mousseron, CNRS UMR5247, Universités Montpellier 1 et 2, Montpellier, France.
authors.forename: Marjorie
authors.initials: M
authors.lastname: Damian
authors.forename: Sophie
authors.initials: S
authors.lastname: Mary
authors.forename: Aimée
authors.initials: A
authors.lastname: Martin
authors.forename: Jean-Philippe
authors.initials: JP
authors.lastname: Pin
authors.forename: Jean-Louis
authors.initials: JL
authors.lastname: Banères
mesh_terms: D002384:Catalysis; D019281:Dimerization; D019204:GTP-Binding Proteins / Q000737:chemistry / Q000378:metabolism*; D016244:Guanosine 5'-O-(3-Thiotriphosphate) / Q000378:metabolism; D006153:Guanosine Diphosphate / Q000737:chemistry; D006160:Guanosine Triphosphate / Q000737:chemistry; D006801:Humans; D007700:Kinetics; D007975:Leukotriene B4 / Q000737:chemistry*; D008024:Ligands; D008856:Microscopy, Fluorescence; D008954:Models, Biological; D008968:Molecular Conformation; D011485:Protein Binding; D015533:Transcriptional Activation
chemical_list: D008024:Ligands; D006153:Guanosine Diphosphate; D007975:Leukotriene B4; D016244:Guanosine 5'-O-(3-Thiotriphosphate); D006160:Guanosine Triphosphate; D019204:GTP-Binding Proteins