Naturally occurring disulfide-bound dimers of three-fingered toxins: a paradigm for biological activity diversification.
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.
Osipov
Alexey V
AV
Shemyakin-Ovchinnikov Institute of Bioorganic Chemistry, Russian Academy of Sciences, Moscow, Russia.
Kasheverov
Igor E
IE
Makarova
Yana V
YV
Starkov
Vladislav G
VG
Vorontsova
Olga V
OV
Ziganshin
Rustam Kh
RKh
Andreeva
Tatyana V
TV
Serebryakova
Marina V
MV
Benoit
Audrey
A
Hogg
Ronald C
RC
Bertrand
Daniel
D
Tsetlin
Victor I
VI
Utkin
Yuri N
YN
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
D003039:Cobra Neurotoxin Proteins; D004220:Disulfides; C025154:alpha-cobratoxin