Li Jing, Zhang Huayuan, Liu Jing, Xu Kangsen
School of Life Science, University of Science and Technology of China, Hefei 230026, Anhui province, People's Republic of China.
Biochem J. 2006 Sep 1;398(2):233-42. doi: 10.1042/BJ20060004.
Three-finger toxins are a family of low-molecular-mass toxins (<10 kDa) having very similar three-dimensional structures. In the present study, 19 novel cDNAs coding three-finger toxins were cloned from the venom gland of Ophiophagus hannah (king cobra). Alignment analysis showed that the putative peptides could be divided into six kinds of three-finger toxins: LNTXs (long-chain neurotoxins), short-chain neurotoxins, cardiotoxins (CTXs), weak neurotoxins, muscarinic toxins and a toxin with a free SH group. Furthermore, a phylogenetic tree was established on the basis of the toxin cDNAs and the previously reported similar nucleotide sequences from the same source venom. It indicated that three-finger-toxin genes in O. hannah diverged early in the course of evolution by long- and short-type pathways. Two LNTXs, namely rLNTX1 (recombinant LNTX1) and rLNTX3, were expressed and showed cytolytic activity in addition to their neurotoxic function. By comparing the functional residues, we offer some possible explanations for the differences in their neurotoxic function. Moreover, a plausible elucidation of the additonal cytolytic activity was achieved by hydropathy-profile analysis. This, to our knowledge, is the first observation that recombinant long chain alpha-neurotoxins have a CTX-like cytolytic activity.
三指毒素是一类低分子量毒素（<10 kDa），具有非常相似的三维结构。在本研究中，从眼镜王蛇的毒腺中克隆出19个编码三指毒素的新cDNA。序列比对分析表明，推测的肽段可分为六种三指毒素：长链神经毒素（LNTXs）、短链神经毒素、心脏毒素（CTXs）、弱神经毒素、毒蕈碱毒素和一种带有游离SH基团的毒素。此外，基于毒素cDNA和先前报道的来自同一来源毒液的相似核苷酸序列构建了系统发育树。结果表明，眼镜王蛇中的三指毒素基因在进化过程中通过长型和短型途径早期发生了分化。两种LNTXs，即重组LNTX1（rLNTX1）和rLNTX3，被表达出来，除了具有神经毒性功能外，还表现出细胞溶解活性。通过比较功能残基，我们对它们神经毒性功能的差异提供了一些可能的解释。此外，通过亲水性分析对额外的细胞溶解活性进行了合理的阐释。据我们所知，这是首次观察到重组长链α-神经毒素具有类似CTX的细胞溶解活性。
