title: Oligomeric structure of the alpha1b-adrenoceptor: comparisons with rhodopsin.
abstract: The structural basis of the quaternary organization of rhodopsin has recently been explored and modeled. Because information obtained from studying rhodopsin has frequently been directly applicable to other G protein-coupled receptors we wished to ascertain if dimeric and/or oligomeric forms of the alpha(1b)-adrenoceptor could be observed and if so whether rhodopsin might provide insights into the quaternary structure of this receptor. Co-immunoprecipitation and both conventional and time-resolved fluorescence resonance energy transfer studies demonstrated quaternary structure of the alpha(1b)-adrenoceptor and, in concert with the reconstitution of fragments of this receptor, provided information on the molecular basis of these interactions. Development of three color fluorescence resonance energy transfer (FRET) allowed the imaging of alpha(1b)-adrenoceptor oligomers in single living cells. Mutation of hydrophobic residues in transmembrane domains I and IV of the receptor resulted in marked reduction in three color FRET suggesting an alteration in oligomeric organization and potential similarities with rhodopsin. The mutated alpha(1b)-adrenoceptor was unable to reach the cell surface, did not become terminally N-glycosylated and was unable to signal.
authors.affiliation: Molecular Pharmacology Group, Division of Biochemistry and Molecular Biology, Institute of Biomedical and Life Sciences, University of Glasgow, Glasgow G12 8QQ, Scotland, UK. g.milligan@bio.gla.ac.uk
authors.forename: Graeme
authors.initials: G
authors.lastname: Milligan
authors.forename: John D
authors.initials: JD
authors.lastname: Pediani
authors.forename: Meritxell
authors.initials: M
authors.lastname: Canals
authors.forename: Juan F
authors.initials: JF
authors.lastname: Lopez-Gimenez
mesh_terms: D000818:Animals; D002462:Cell Membrane / Q000378:metabolism; D019281:Dimerization; D006801:Humans; D009154:Mutation; D020836:Protein Structure, Quaternary; D018340:Receptors, Adrenergic, alpha-1 / Q000737:chemistry* / Q000235:genetics; D012243:Rhodopsin / Q000737:chemistry*; D012374:Rod Cell Outer Segment / Q000378:metabolism; D014785:Vision, Ocular / Q000502:physiology
chemical_list: C547716:ADRA1B protein, human; D018340:Receptors, Adrenergic, alpha-1; D012243:Rhodopsin