title: A role for amino acid residues in the third cytoplasmic loop in defining the ligand binding characteristics of the alpha2D-adrenergic receptor.
abstract: In this report, 5 amino acid residues (aa) in the third cytoplasmic loop of the alpha 2D-adrenergic receptor are identified which (individually or together) alter its ligand-binding characteristics. An important structural discrepancy exists in the third cytoplasmic loop of the alpha 2D-ARs encoded by the rat cDNA and the rat gene--five aa are different. The newly identified bovine receptor as well as the mouse receptor contained the 5 aa identical to that encoded by the rat cDNA. Site-directed mutation of these residues to those of the rat gene encoded receptor resulted in alteration of binding characteristics: significant changes in the ability of the mutant receptor to bind to a number of agonists and antagonists were observed--ranging from a decrease by half in the case of oxymetazoline, to near total loss of binding in the case of prazosin. Thus, the mutant receptor was no longer pure alpha 2D-AR. This indicated a hitherto unrealized role of the third cytoplasmic loop in defining the ligand-binding characteristics of the receptor, and also suggested that the rat gene sequence was most probably in error.
authors.affiliation: Department of Cell Biology, University of Medicine and Dentistry of New Jersey, Stratford 08084, USA.
authors.forename: V
authors.initials: V
authors.lastname: Venkataraman
authors.forename: T
authors.initials: T
authors.lastname: Duda
authors.forename: R K
authors.initials: RK
authors.lastname: Sharma
mesh_terms: D000595:Amino Acid Sequence; D000596:Amino Acids / Q000378:metabolism / Q000502:physiology*; D000818:Animals; D019556:COS Cells; D002417:Cattle; D003000:Clonidine / Q000031:analogs & derivatives / Q000494:pharmacology; D003593:Cytoplasm / Q000378:metabolism; D004837:Epinephrine / Q000494:pharmacology; D006801:Humans; D008024:Ligands; D051379:Mice; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D010109:Oxymetazoline / Q000494:pharmacology; D010646:Phentolamine / Q000494:pharmacology; D011224:Prazosin / Q000494:pharmacology; D011485:Protein Binding / Q000187:drug effects / Q000235:genetics; D051381:Rats; D018341:Receptors, Adrenergic, alpha-2 / Q000187:drug effects / Q000235:genetics / Q000502:physiology*; D016415:Sequence Alignment; D015016:Yohimbine / Q000494:pharmacology
chemical_list: D000596:Amino Acids; D008024:Ligands; D018341:Receptors, Adrenergic, alpha-2; D015016:Yohimbine; C016986:apraclonidine; D010109:Oxymetazoline; D003000:Clonidine; D011224:Prazosin; D004837:Epinephrine; D010646:Phentolamine