Comparison of the hemolytic activity and solution structures of two snake venom cardiotoxin analogues which only differ in their N-terminal amino acid.
Comparison of the hemolytic activity and solution structures of two snake venom cardiotoxin analogues which only differ in their N-terminal amino acid.
复制标题
两种蛇毒心脏毒素类似物（仅 N 端氨基酸不同）的溶血活性和溶液结构的比较。
作者：
J. Jang;T. Krishnaswamy;S. Kumar;Gurunathan Jayaraman;P. Yang;Chin Yu
从台湾眼镜蛇（Naja naja atra）毒液中分离出的眼镜蛇毒素类似物IV（CTX IV）和II（CTX II）的氨基酸序列在N-末端有一个氨基酸不同。CTX II中N-末端的亮氨酸在CTX IV中被精氨酸取代。CTX IV是一种独特的蛇毒心脏毒素，因为它是迄今为止已知的唯一在N-末端氨基酸处具有带正电荷的残基的心脏毒素同种型。所有其他心脏毒素的N末端都有一个疏水性氨基酸（亮氨酸或异亮氨酸）。本研究的目的是了解阳离子残基的存在对心脏毒素的结构和功能特性的影响。比较CTX Ⅳ和CTX Ⅱ的溶血活性，前者的溶血活性至少是后者的两倍。CTX IV和CTX II的溶液结构，使用二维NMR光谱和动态模拟退火技术的比较表明，这两种毒素异构体的骨架折叠几乎是相似的。这两种心脏毒素同种型的二级结构元件由长的三链以及短的双链反平行β折叠组成。热变性实验表明，CTX IV的结构比CTX II更稳定。CTX IV和CTX II的三维结构的临界分析揭示了在CTX IV分子的凹侧上存在由带正电荷的残基组成的"阳离子"簇。在CTX II中没有发现由带正电荷的残基组成的类似簇。这两种心脏毒素的不同红细胞溶解活性归因于其三维结构中带正电荷的残基分布的差异。
Cardiotoxin analogues IV (CTX IV) and II (CTX II) isolated from the venom of Taiwan Cobra (Naja naja atra) differ in their amino acid sequence by a single amino acid at the N-terminal end. Leucine at the N-terminal end in CTX II is replaced by arginine in CTX IV. CTX IV is an unique snake venom cardiotoxin as it is the only cardiotoxin isoform known so far which possesses a positively charged residue at the N-terminal amino acid. All other cardiotoxins have a hydrophobic amino acid (leucine or isoleucine) at their N-terminal end. The aim of the present study is to understand the effect(s) of the presence of a cationic residue on the structure and functional properties of cardiotoxin(s). Comparison of the hemolytic activities of CTX IV and CTX II shows that lytic activity of the former is at least twice as that shown by the latter. Comparison of the solution structures of CTX IV and CTX II using two-dimensional NMR spectroscopy and dynamical simulated annealing technique reveals that the backbone fold of both the toxin isoforms is almost similar. The secondary structural elements in these two cardiotoxin isoforms consist of long, triple-stranded, as well as short, double-stranded, antiparallel beta-sheets. Thermal denaturation experiments showed that the structure of CTX IV is more stable than that of CTX II. Critical analysis of the three-dimensional structures of CTX IV and CTX II reveals the presence of a "cationic" cluster comprising of positively charged residues on the concave side of the CTX IV molecule. Similar clusters consisting of positively charged residues are not found in CTX II. The differential erythrocyte lytic activities of these two cardiotoxins are attributed to the difference(s) in the distribution of the positively charged residues in their three-dimensional structures.