title: Constitutive activation of a single effector pathway: evidence for multiple activation states of a G protein-coupled receptor.
abstract: A cysteine-to-phenylalanine mutation in the third transmembrane domain of the alpha 1B-adrenergic receptor constitutively activates the receptor, resulting in G protein coupling in the absence of agonist and activation of only a single effector pathway (phospholipase C but not phospholipase A2). This mutant receptor displays a higher affinity for the catecholamines, norepinephrine, and epinephrine, as well as for other phenethylamines, but not for imidazolines, a class of structurally distinct alpha agonists. Dose-response studies demonstrate a higher potency and intrinsic activity of phenethylamines for polyphosphoinositide turnover but not for arachidonic acid release. Imidazolines have wild-type potencies and intrinsic activities for both pathways. These data indicate that a single receptor subtype forms multiple conformations (i.e., exhibits induced conformational pleiotropy) for G protein interactions (high affinity states) that are specific for a particular G protein/effector pathway and that multiple binding sites exist for agonists, which promote or induce these specific interactions. Pharmacological diversity may, thus, be achieved through a single receptor by the development of compounds that induce a single activated conformer. This has major ramifications for the eventual development of signaling-specific therapeutics.
authors.affiliation: Department of Molecular Cardiology, Cleveland Clinic Research Institute, Ohio 44195, USA.
authors.forename: D M
authors.initials: DM
authors.lastname: Perez
authors.forename: J
authors.initials: J
authors.lastname: Hwa
authors.forename: R
authors.initials: R
authors.lastname: Gaivin
authors.forename: M
authors.initials: M
authors.lastname: Mathur
authors.forename: F
authors.initials: F
authors.lastname: Brown
authors.forename: R M
authors.initials: RM
authors.lastname: Graham
mesh_terms: D000317:Adrenergic alpha-Antagonists / Q000494:pharmacology; D000818:Animals; D016718:Arachidonic Acid / Q000378:metabolism; D001483:Base Sequence; D002460:Cell Line; D017931:DNA Primers; D019204:GTP-Binding Proteins / Q000378:metabolism*; D015544:Inositol 1,4,5-Trisphosphate / Q000096:biosynthesis; D007457:Iodine Radioisotopes; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D010627:Phenethylamines / Q000378:metabolism; D011224:Prazosin / Q000378:metabolism / Q000494:pharmacology; D011869:Radioligand Assay; D018340:Receptors, Adrenergic, alpha-1 / Q000378:metabolism*; D015398:Signal Transduction; D044024:Tetralones; D014316:Tritium; D010566:Virulence Factors, Bordetella / Q000494:pharmacology
chemical_list: D000317:Adrenergic alpha-Antagonists; D017931:DNA Primers; D007457:Iodine Radioisotopes; D010627:Phenethylamines; D018340:Receptors, Adrenergic, alpha-1; D044024:Tetralones; D010566:Virulence Factors, Bordetella; D014316:Tritium; D016718:Arachidonic Acid; C010652:BE 2254; D015544:Inositol 1,4,5-Trisphosphate; D019204:GTP-Binding Proteins; D011224:Prazosin