title: Modeling and mutagenesis of the human alpha 1a-adrenoceptor: orientation and function of transmembrane helix V sidechains.
abstract: A 3-dimensional model of the seven transmembrane helical segments (TMs) of the human alpha 1a-adrenoceptor was initially built by analogy to the known structure of bacteriorhodopsin. However, the rotational orientation of TM V about its helical axis, and the roles of several TM V residues in ligand binding and receptor activation remained in question. Accordingly, we determined the effects of six site-specific mutations in TM V on binding affinity and functional potency of a structurally diverse series of agonists and antagonists. Mutation of Ser 192 and Phe 193 disrupted the binding of many of the tested ligands, as measured by displacement of [3H]prazosin. In addition, mutation of Ser 188, Ser 192, and Phe 193 disrupted receptor activation, as measured by [3H]inositol phosphate formation. On the basis of these results, a specific rotational orientation of TM V is proposed as part of a revised receptor model, which also takes into account more recently reported information about the structure of rhodopsin. This revised alpha 1a-adrenoceptor model accounts for direct interactions which are proposed between Ser 188 and Ser 192 and the meta and para hydroxyl groups of norepinephrine, respectively, in the G-protein coupled receptor state.
authors.affiliation: Department of Chemistry, Synaptic Pharmaceutical Corporation, Paramus, NJ 07652, USA.
authors.forename: J M
authors.initials: JM
authors.lastname: Wetzel
authors.forename: J A
authors.initials: JA
authors.lastname: Salon
authors.forename: J A
authors.initials: JA
authors.lastname: Tamm
authors.forename: C
authors.initials: C
authors.lastname: Forray
authors.forename: D
authors.initials: D
authors.lastname: Craig
authors.forename: H
authors.initials: H
authors.lastname: Nakanishi
authors.forename: W
authors.initials: W
authors.lastname: Cui
authors.forename: P J
authors.initials: PJ
authors.lastname: Vaysse
authors.forename: G
authors.initials: G
authors.lastname: Chiu
authors.forename: R L
authors.initials: RL
authors.lastname: Weinshank
authors.forename: P R
authors.initials: PR
authors.lastname: Hartig
authors.forename: T A
authors.initials: TA
authors.lastname: Branchek
authors.forename: C
authors.initials: C
authors.lastname: Gluchowski
mesh_terms: D000595:Amino Acid Sequence; D006801:Humans; D008958:Models, Molecular; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D011224:Prazosin / Q000494:pharmacology; D017433:Protein Structure, Secondary / Q000187:drug effects; D011869:Radioligand Assay; D018340:Receptors, Adrenergic, alpha-1 / Q000737:chemistry* / Q000187:drug effects / Q000235:genetics* / Q000502:physiology
chemical_list: D018340:Receptors, Adrenergic, alpha-1; D011224:Prazosin