title: Azemiopsin from Azemiops feae viper venom, a novel polypeptide ligand of nicotinic acetylcholine receptor.
abstract: Azemiopsin, a novel polypeptide, was isolated from the Azemiops feae viper venom by combination of gel filtration and reverse-phase HPLC. Its amino acid sequence (DNWWPKPPHQGPRPPRPRPKP) was determined by means of Edman degradation and mass spectrometry. It consists of 21 residues and, unlike similar venom isolates, does not contain cysteine residues. According to circular dichroism measurements, this peptide adopts a β-structure. Peptide synthesis was used to verify the determined sequence and to prepare peptide in sufficient amounts to study its biological activity. Azemiopsin efficiently competed with α-bungarotoxin for binding to Torpedo nicotinic acetylcholine receptor (nAChR) (IC(50) 0.18 ± 0.03 μm) and with lower efficiency to human α7 nAChR (IC(50) 22 ± 2 μm). It dose-dependently blocked acetylcholine-induced currents in Xenopus oocytes heterologously expressing human muscle-type nAChR and was more potent against the adult form (α1β1εδ) than the fetal form (α1β1γδ), EC(50) being 0.44 ± 0.1 μm and 1.56 ± 0.37 μm, respectively. The peptide had no effect on GABA(A) (α1β3γ2 or α2β3γ2) receptors at a concentration up to 100 μm or on 5-HT(3) receptors at a concentration up to 10 μm. Ala scanning showed that amino acid residues at positions 3-6, 8-11, and 13-14 are essential for binding to Torpedo nAChR. In biological activity azemiopsin resembles waglerin, a disulfide-containing peptide from the Tropidechis wagleri venom, shares with it a homologous C-terminal hexapeptide, but is the first natural toxin that blocks nAChRs and does not possess disulfide bridges.
authors.affiliation: Shemyakin-Ovchinnikov Institute of Bioorganic Chemistry, Russian Academy of Sciences, Moscow 117997, Russia. utkin@mx.ibch.ru
authors.forename: Yuri N
authors.initials: YN
authors.lastname: Utkin
authors.forename: Christoph
authors.initials: C
authors.lastname: Weise
authors.forename: Igor E
authors.initials: IE
authors.lastname: Kasheverov
authors.forename: Tatyana V
authors.initials: TV
authors.lastname: Andreeva
authors.forename: Elena V
authors.initials: EV
authors.lastname: Kryukova
authors.forename: Maxim N
authors.initials: MN
authors.lastname: Zhmak
authors.forename: Vladislav G
authors.initials: VG
authors.lastname: Starkov
authors.forename: Ngoc Anh
authors.initials: NA
authors.lastname: Hoang
authors.forename: Daniel
authors.initials: D
authors.lastname: Bertrand
authors.forename: Joachim
authors.initials: J
authors.lastname: Ramerstorfer
authors.forename: Werner
authors.initials: W
authors.lastname: Sieghart
authors.forename: Andrew J
authors.initials: AJ
authors.lastname: Thompson
authors.forename: Sarah C R
authors.initials: SC
authors.lastname: Lummis
authors.forename: Victor I
authors.initials: VI
authors.lastname: Tsetlin
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D002851:Chromatography, High Pressure Liquid; D002942:Circular Dichroism; D008024:Ligands; D008297:Male; D051379:Mice; D008807:Mice, Inbred BALB C; D008969:Molecular Sequence Data; D010455:Peptides / Q000737:chemistry / Q000378:metabolism / Q000494:pharmacology*; D011978:Receptors, Nicotinic / Q000378:metabolism*; D017386:Sequence Homology, Amino Acid; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization; D014757:Viper Venoms / Q000737:chemistry* / Q000378:metabolism / Q000494:pharmacology
chemical_list: D008024:Ligands; D010455:Peptides; D011978:Receptors, Nicotinic; D014757:Viper Venoms; C576053:azemiopsin protein, Azemiops feae