TY - JOUR T1 - Multiple Interactions between Transmembrane Helices Generate the Oligomeric α<sub>1b</sub>-Adrenoceptor JF - Molecular Pharmacology JO - Mol Pharmacol SP - 1123 LP - 1137 DO - 10.1124/mol.104.001586 VL - 66 IS - 5 AU - Juan J. Carrillo AU - Juan F. López-Giménez AU - Graeme Milligan Y1 - 2004/11/01 UR - http://molpharm.aspetjournals.org/content/66/5/1123.abstract N2 - 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 α1b-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 α1b-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 α1b-adrenoceptor, and with a contribution of transmembrane domains 5 and/or 6. These data are consistent with a complex oligomeric quaternary structure of the α1b-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. ER -