title: Antagonist conformations with the beta(2)-adrenergic receptor ligand binding pocket.
abstract: The interactions between beta-adrenergic receptor (beta AR) antagonists and the beta(2)AR were studied with the use of photoaffinity labels. A proteolytic map of the receptor was made and confirmed through amino-terminal amino acid sequencing by locating sites of derivatization. [125I]Iodoazidothiophenylalprenolol (IAPTA) is a photoaffinity derivative of the beta AR antagonist alprenolol with a photoactivatable group on the aryloxy end of the molecule. IAPTA exclusively derivatizes a peptide consisting of transmembrane domains (TMs) 6 and 7 of the hamster lung beta(2)AR, supporting the contention that TMs 6 and 7 interact with the aryloxy portion of the beta AR antagonist pharmacophore. The beta AR antagonist photoaffinity labels [125I]iodoazidobenzylpindolol (IABP), [125I]iodoazidophenyl CGP-12177A (IAPCGP), and [125I]iodocyanopindololdiazarene (ICYPdz) are similar in that their photoactive moieties are attached to the amino end of the antagonist pharmacophore. IABP derivatized TMs 5-7 and a peptide containing TM 1 to approximately equal extents. IAPCGP derivatized Tms 6 and 7 >> TM 5 = TM 4 = TMs 2 and 3 = TM 1. ICYPdz derivatized TM 1 >> TMs 6 and 7 > Tm 4. We conclude that the aryloxy end of the beta AR antagonist pharmacophore is highly constrained within TMs 6 and 7, whereas the amino terminus is much less constrained and able to assume multiple conformations. Molecular dynamics simulations predict that IABP, IAPCGP, and ICYPdz favor a folded conformation, with both ends close together. Derivatization of TMs 6 and 7 by IABP, IAPCGP, and ICYPdz suggests the folded conformation of these compounds in the ligand binding pocket.
authors.affiliation: Department of Pharmacology, University of Wisconsin School of Medicine, Madison, 53706, USA.
authors.forename: G H
authors.initials: GH
authors.lastname: Hockerman
authors.forename: M E
authors.initials: ME
authors.lastname: Girvin
authors.forename: C C
authors.initials: CC
authors.lastname: Malbon
authors.forename: A E
authors.initials: AE
authors.lastname: Ruoho
mesh_terms: D058672:Adrenergic beta-2 Receptor Antagonists; D000319:Adrenergic beta-Antagonists / Q000737:chemistry*; D000345:Affinity Labels; D000595:Amino Acid Sequence; D000818:Animals; D006224:Cricetinae; D008968:Molecular Conformation; D008969:Molecular Sequence Data; D008970:Molecular Weight; D010449:Peptide Mapping; D018343:Receptors, Adrenergic, beta-2 / Q000737:chemistry; D012697:Serine Endopeptidases / Q000494:pharmacology; D018411:Spodoptera; D014357:Trypsin / Q000494:pharmacology
chemical_list: D058672:Adrenergic beta-2 Receptor Antagonists; D000319:Adrenergic beta-Antagonists; D000345:Affinity Labels; D018343:Receptors, Adrenergic, beta-2; D012697:Serine Endopeptidases; C028344:glutamyl endopeptidase; D014357:Trypsin