Multiple interactions between transmembrane helices generate the oligomeric alpha1b-adrenoceptor.
Combinations of coimmunoprecipitation, single-cell fluorescence resonance energy transfer, and cell-surface time-resolved fluorescence resonance energy transfer demonstrated protein-protein interactions and quaternary structure for the alpha(1b)-adrenoceptor. Self-association of transmembrane domain 1 and its interaction with the full-length receptor indicated a symmetrical interface provided by this domain. Lack of effect of mutation of the glycophorin-A dimerization-like region within this helix demonstrated that this did not provide the molecular mechanism. Multiple interactions were observed between the alpha(1b)-adrenoceptor and fragments derived from its sequence. Fragments comprising transmembrane domains 3 and 4 and transmembrane domains 5 and 6, but not transmembrane domain 7, were also able to interact with the full-length receptor. Transmembrane domain 7 failed to interact significantly with any element of the receptor and was not transported to the cell surface after coexpression with the full-length receptor. Symmetrical interactions were also noted between fragments incorporating transmembrane domain 4, but this segment of the receptor failed to interact with transmembrane domains 1 and 2 or transmembrane domains 5 and 6. Time-resolved fluorescence resonance energy transfer studies were also consistent with contributions of transmembrane domains 1 and/or 2 and transmembrane domains 3 and/or 4 to protein-protein interactions within the quaternary structure of the alpha(1b)-adrenoceptor, and with a contribution of transmembrane domains 5 and/or 6. These data are consistent with a complex oligomeric quaternary structure of the alpha(1b)-adrenoceptor in which major, symmetrical interactions may define intradimeric contacts with other contributions, providing interdimer contacts to generate oligomeric complexes akin to those observed for murine rhodopsin. A model derived from this was developed.
Carrillo
Juan J
JJ
Molecular Pharmacology Group, Division of Biochemistry and Molecular Biology, Institute of Biomedical and Life Sciences, University of Glasgow, Glasgow G12 8QQ, Scotland, United Kingdom.
López-Giménez
Juan F
JF
Milligan
Graeme
G
D000818:Animals; D002478:Cells, Cultured; D006224:Cricetinae; D019281:Dimerization; D006801:Humans; D008565:Membrane Proteins / Q000737:chemistry / Q000378:metabolism*; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D018340:Receptors, Adrenergic, alpha-1 / Q000737:chemistry / Q000378:metabolism*
C547716:ADRA1B protein, human; D008565:Membrane Proteins; D018340:Receptors, Adrenergic, alpha-1