title: Ligand recognition of serine-cysteine amino acid exchanges in transmembrane domain 5 of alpha2-adrenergic receptors by UK 14,304.
abstract: Ligand binding of UK 14,304 reveals notable species (i.e., human-rodent) and receptor-subtype differences of alpha2-adrenergic receptors (alpha2-ARs). To study the molecular basis of the selectivity of UK 14,304, we compared a series of conservative serine-cysteine exchange mutants at ligand-accessible positions in transmembrane domain 5 of the human and mouse alpha2A-ARs. UK 14,304 bound with approximately 200-fold higher affinity to the human alpha2A-AR wild-type receptor compared with the human alpha2A-ARSer201 mutant, but only an approximately fivefold difference was seen with the corresponding mouse alpha2A-AR variant. These effects of cysteine-serine exchanges only involved the agonist low-affinity forms of the receptors, as the affinity of [3H]UK 14,304 for the agonist high-affinity receptor populations was not influenced. The apparent affinities of a set of eight structurally diverse alpha2-AR ligands (six agonists and two antagonists) were not influenced significantly by the cysteine-serine exchanges (except for oxymetazoline and yohimbine, with up to nine- and eightfold differences in affinity, respectively). We conclude that position 201 (a) plays a primary role in determining observed subtype/species selectivity of UK 14,304 in competitive antagonist radioligand binding assays and (b) does not determine the subtype selectivity of chlorpromazine.
authors.affiliation: Orion Pharma, University of Turku, Finland. victor.cockcroft@basf-pharma.co.uk
authors.forename: V
authors.initials: V
authors.lastname: Cockcroft
authors.forename: H
authors.initials: H
authors.lastname: Frang
authors.forename: M
authors.initials: M
authors.lastname: Pihlavisto
authors.forename: A
authors.initials: A
authors.lastname: Marjamäki
authors.forename: M
authors.initials: M
authors.lastname: Scheinin
mesh_terms: D000316:Adrenergic alpha-Agonists / Q000378:metabolism / Q000494:pharmacology*; D000317:Adrenergic alpha-Antagonists / Q000494:pharmacology; D000818:Animals; D001665:Binding Sites / Q000502:physiology; D001667:Binding, Competitive; D000068438:Brimonidine Tartrate; D016466:CHO Cells; D002746:Chlorpromazine / Q000378:metabolism / Q000494:pharmacology; D006224:Cricetinae; D003545:Cysteine / Q000378:metabolism*; D018492:Dopamine Antagonists / Q000378:metabolism / Q000494:pharmacology; D006801:Humans; D019329:Idazoxan / Q000031:analogs & derivatives / Q000378:metabolism / Q000494:pharmacology; D008024:Ligands; D051379:Mice; D008958:Models, Molecular; D008969:Molecular Sequence Data; D010109:Oxymetazoline / Q000378:metabolism / Q000494:pharmacology; D017434:Protein Structure, Tertiary; D011810:Quinoxalines / Q000378:metabolism / Q000494:pharmacology*; D011869:Radioligand Assay; D018341:Receptors, Adrenergic, alpha-2 / Q000737:chemistry / Q000378:metabolism*; D017386:Sequence Homology, Amino Acid; D012694:Serine / Q000378:metabolism*; D014162:Transfection; D014316:Tritium; D015016:Yohimbine / Q000378:metabolism / Q000494:pharmacology
chemical_list: D000316:Adrenergic alpha-Agonists; D000317:Adrenergic alpha-Antagonists; D018492:Dopamine Antagonists; D008024:Ligands; D011810:Quinoxalines; D018341:Receptors, Adrenergic, alpha-2; D014316:Tritium; D015016:Yohimbine; D012694:Serine; D000068438:Brimonidine Tartrate; D010109:Oxymetazoline; C058525:2-methoxyidazoxan; D003545:Cysteine; D002746:Chlorpromazine; D019329:Idazoxan