title: Naturally occurring disulfide-bound dimers of three-fingered toxins: a paradigm for biological activity diversification.
abstract: Disulfide-bound dimers of three-fingered toxins have been discovered in the Naja kaouthia cobra venom; that is, the homodimer of alpha-cobratoxin (a long-chain alpha-neurotoxin) and heterodimers formed by alpha-cobratoxin with different cytotoxins. According to circular dichroism measurements, toxins in dimers retain in general their three-fingered folding. The functionally important disulfide 26-30 in polypeptide loop II of alpha-cobratoxin moiety remains intact in both types of dimers. Biological activity studies showed that cytotoxins within dimers completely lose their cytotoxicity. However, the dimers retain most of the alpha-cobratoxin capacity to compete with alpha-bungarotoxin for binding to Torpedo and alpha7 nicotinic acetylcholine receptors (nAChRs) as well as to Lymnea stagnalis acetylcholine-binding protein. Electrophysiological experiments on neuronal nAChRs expressed in Xenopus oocytes have shown that alpha-cobratoxin dimer not only interacts with alpha7 nAChR but, in contrast to alpha-cobratoxin monomer, also blocks alpha3beta2 nAChR. In the latter activity it resembles kappa-bungarotoxin, a dimer with no disulfides between monomers. These results demonstrate that dimerization is essential for the interaction of three-fingered neurotoxins with heteromeric alpha3beta2 nAChRs.
authors.affiliation: Shemyakin-Ovchinnikov Institute of Bioorganic Chemistry, Russian Academy of Sciences, Moscow, Russia.
authors.forename: Alexey V
authors.initials: AV
authors.lastname: Osipov
authors.forename: Igor E
authors.initials: IE
authors.lastname: Kasheverov
authors.forename: Yana V
authors.initials: YV
authors.lastname: Makarova
authors.forename: Vladislav G
authors.initials: VG
authors.lastname: Starkov
authors.forename: Olga V
authors.initials: OV
authors.lastname: Vorontsova
authors.forename: Rustam Kh
authors.initials: RKh
authors.lastname: Ziganshin
authors.forename: Tatyana V
authors.initials: TV
authors.lastname: Andreeva
authors.forename: Marina V
authors.initials: MV
authors.lastname: Serebryakova
authors.forename: Audrey
authors.initials: A
authors.lastname: Benoit
authors.forename: Ronald C
authors.initials: RC
authors.lastname: Hogg
authors.forename: Daniel
authors.initials: D
authors.lastname: Bertrand
authors.forename: Victor I
authors.initials: VI
authors.lastname: Tsetlin
authors.forename: Yuri N
authors.initials: YN
authors.lastname: Utkin
mesh_terms: D000818:Animals; D002850:Chromatography, Gel; D002851:Chromatography, High Pressure Liquid; D002942:Circular Dichroism; D003039:Cobra Neurotoxin Proteins / Q000737:chemistry* / Q000302:isolation & purification / Q000378:metabolism*; D019281:Dimerization; D004220:Disulfides / Q000737:chemistry* / Q000378:metabolism*; D017815:Elapidae; D006801:Humans; D008958:Models, Molecular; D017434:Protein Structure, Tertiary; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization
chemical_list: D003039:Cobra Neurotoxin Proteins; D004220:Disulfides; C025154:alpha-cobratoxin