title: Allosteric alpha 1-adrenoreceptor antagonism by the conopeptide rho-TIA.
abstract: A peptide contained in the venom of the predatory marine snail Conus tulipa, rho-TIA, has previously been shown to possess alpha1-adrenoreceptor antagonist activity. Here, we further characterize its pharmacological activity as well as its structure-activity relationships. In the isolated rat vas deferens, rho-TIA inhibited alpha1-adrenoreceptor-mediated increases in cytosolic Ca2+ concentration that were triggered by norepinephrine, but did not affect presynaptic alpha2-adrenoreceptor-mediated responses. In radioligand binding assays using [125I]HEAT, rho-TIA displayed slightly greater potency at the alpha 1B than at the alpha 1A or alpha 1D subtypes. Moreover, although it did not affect the rate of association for [3H]prazosin binding to the alpha 1B-adrenoreceptor, the dissociation rate was increased, indicating non-competitive antagonism by rho-TIA. N-terminally truncated analogs of rho-TIA were less active than the full-length peptide, with a large decline in activity observed upon removal of the fourth residue of rho-TIA (Arg4). An alanine walk of rho-TIA confirmed the importance of Arg4 for activity and revealed a number of other residues clustered around Arg4 that contribute to the potency of rho-TIA. The unique allosteric antagonism of rho-TIA resulting from its interaction with receptor residues that constitute a binding site that is distinct from that of the classical competitive alpha1-adrenoreceptor antagonists may allow the development of inhibitors that are highly subtype selective.
authors.affiliation: Institute for Molecular Bioscience and the School of Biomedical Sciences, The University of Queensland, St. Lucia 4072, Queensland, Australia.
authors.forename: Iain A
authors.initials: IA
authors.lastname: Sharpe
authors.forename: Linda
authors.initials: L
authors.lastname: Thomas
authors.forename: Marion
authors.initials: M
authors.lastname: Loughnan
authors.forename: Leonid
authors.initials: L
authors.lastname: Motin
authors.forename: Elka
authors.initials: E
authors.lastname: Palant
authors.forename: Daniel E
authors.initials: DE
authors.lastname: Croker
authors.forename: Dianne
authors.initials: D
authors.lastname: Alewood
authors.forename: Songhai
authors.initials: S
authors.lastname: Chen
authors.forename: Robert M
authors.initials: RM
authors.lastname: Graham
authors.forename: Paul F
authors.initials: PF
authors.lastname: Alewood
authors.forename: David J
authors.initials: DJ
authors.lastname: Adams
authors.forename: Richard J
authors.initials: RJ
authors.lastname: Lewis
mesh_terms: D058668:Adrenergic alpha-1 Receptor Antagonists; D000409:Alanine / Q000737:chemistry; D000495:Allosteric Site; D000595:Amino Acid Sequence; D000818:Animals; D001120:Arginine / Q000737:chemistry; D001665:Binding Sites; D001667:Binding, Competitive; D019556:COS Cells; D002462:Cell Membrane / Q000378:metabolism; D002478:Cells, Cultured; D020916:Conotoxins / Q000737:chemistry* / Q000378:metabolism*; D003553:Cystine / Q000737:chemistry; D004305:Dose-Response Relationship, Drug; D007700:Kinetics; D008297:Male; D008856:Microscopy, Fluorescence; D008958:Models, Molecular; D008969:Molecular Sequence Data; D009130:Muscle, Smooth / Q000166:cytology; D010452:Peptide Biosynthesis; D010455:Peptides / Q000737:chemistry / Q000378:metabolism; D011485:Protein Binding; D011487:Protein Conformation; D017434:Protein Structure, Tertiary; D051381:Rats; D017208:Rats, Wistar; D018340:Receptors, Adrenergic, alpha-1 / Q000737:chemistry*; D013329:Structure-Activity Relationship; D013997:Time Factors; D014649:Vas Deferens / Q000378:metabolism
chemical_list: D058668:Adrenergic alpha-1 Receptor Antagonists; D020916:Conotoxins; D010455:Peptides; D018340:Receptors, Adrenergic, alpha-1; C477745:conotoxin rho-TIA; D003553:Cystine; D001120:Arginine; D000409:Alanine