Naturally Occurring Disulfide-bound Dimers of Three-fingered Toxins
A PARADIGM FOR BIOLOGICAL ACTIVITY DIVERSIFICATION*
- Alexey V. Osipov‡,
- Igor E. Kasheverov‡,
- Yana V. Makarova‡,
- Vladislav G. Starkov‡,
- Olga V. Vorontsova‡,
- Rustam Kh. Ziganshin‡,
- Tatyana V. Andreeva‡,
- Marina V. Serebryakova§,
- Audrey Benoit¶,
- Ronald C. Hogg¶,
- Daniel Bertrand¶,
- Victor I. Tsetlin‡ and
- Yuri N. Utkin‡,1
- ‡Shemyakin-Ovchinnikov Institute of Bioorganic Chemistry, Russian Academy of Sciences, Moscow, 117997 Russia, §Scientific Research Institute of Physico-Chemical Medicine, Moscow, 119992 Russia, and ¶Department of Neuroscience, Centre Medical Universitaire, Medical Faculty, CH-1211 Geneva 4, Switzerland
- ↵1 To whom correspondence should be addressed: Shemyakin-Ovchinnikov Institute of Bioorganic Chemistry, Russian Academy of Sciences, ul. Miklukho-Maklaya 16/10, Moscow, 117997 Russia. Tel.: 007-495-3366522; Fax: 007-495-3355733; E-mail: utkin{at}mx.ibch.ru.
Abstract
Disulfide-bound dimers of three-fingered toxins have been discovered in the Naja kaouthia cobra venom; that is, the homodimer of α-cobratoxin (a long-chain α-neurotoxin) and heterodimers formed by α-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 α-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 α-cobratoxin capacity to compete with α-bungarotoxin for binding to Torpedo and α7 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 α-cobratoxin dimer not only interacts with α7 nAChR but, in contrast to α-cobratoxin monomer, also blocks α3β2 nAChR. In the latter activity it resembles κ-bungarotoxin, a dimer with no disulfides between monomers. These results demonstrate that dimerization is essential for the interaction of three-fingered neurotoxins with heteromeric α3β2 nAChRs.
Footnotes
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↵* This work was supported by Russian Foundation for Basic Research (Grants 08-04-00801, 06-04-48982, and 07-04-00741) and INTAS (Grant 05-1000008-7919). This work was also supported by the Swiss National Science Foundation (to R. H. and D. B.). The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked “advertisement” in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.
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The on-line version of this article (available at http://www.jbc.org) contains supplemental Figs. S1 and S2, Scheme SI, and Tables SI and SII.
- Received March 17, 2008.
- The American Society for Biochemistry and Molecular Biology, Inc.
