Naturally occurring disulfide-bound dimers of three-fingered toxins - A paradigm for biological activity diversification
Naturally occurring disulfide-bound dimers of three-fingered toxins - A paradigm for biological activity diversification
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DOI：
10.1074/jbc.m802085200
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发表时间：
2008-05-23
影响因子：
4.8
通讯作者：
Utkin, Yuri N.
中科院分区：
文献类型：
--
作者：
Osipov, Alexey V.;Kasheverov, Igor E.;Utkin, Yuri N.
在眼镜蛇蛇毒中发现了三指毒素的二硫键结合二聚体，即α-眼镜蛇毒素(一种长链α-神经毒素)的同源二聚体和α-眼镜蛇毒素与不同细胞毒素形成的杂二聚体。根据圆二色谱测量，二聚体中的毒素一般保持其三指折叠。在两种类型的二聚体中，α-眼镜蛇毒多肽环II中具有重要功能的二硫键26-30在两种类型的二聚体中都保持不变。生物活性研究表明，二聚体中的细胞毒素完全失去了细胞毒性。然而，这些二聚体保留了大部分与α-银环蛇毒素竞争结合鱼雷和α7烟碱型乙酰胆碱受体(NAChRs)以及凝固性淋巴毒素乙酰胆碱结合蛋白的能力。对非洲爪哇卵母细胞表达的神经元nAChRs的电生理实验表明，α-眼镜蛇毒二聚体不仅与α-7 nAChR相互作用，而且与α-眼镜蛇毒单体相反，还能阻断α-3-β2 nAChR。在后一种活性上，它类似于卡帕-银环蛇毒素，一种二聚体，在单体之间没有二硫键。这些结果表明，二聚化是三指神经毒素与异构体α3β2 nAChRs相互作用的关键。
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 alpha 7 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 alpha 7 nAChR but, in contrast to alpha-cobratoxin monomer, also blocks alpha 3 beta 2 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 alpha 3 beta 2 nAChRs.