Vogel C W, Smith C A, Müller-Eberhard H J
J Immunol. 1984 Dec;133(6):3235-41.
The functional analogy between cobra venom factor (CVF), the complement-activating protein in cobra venom, and C3b, the activated form of the third complement component, prompted us to conduct a comparative analysis of structural properties of the two proteins derived from two phylogenetically distant species. We subjected CVF and human C3 and its physiologic cleavage products, C3b and C3c, to a variety of biochemical analyses. We report here structural similarities of these proteins, which include similarities in amino acid composition, far and near UV circular dichroism spectra, secondary structure, band patterns and pI values from isoelectric focusing, immunochemical cross-reactivity, ultrastructural morphology, and amino-terminal amino acid sequences. Analysis of these data reveals that, structurally, CVF resembles C3c more than C3b. We conclude that CVF is not the product of a convergent evolution, but is, in all likelihood, derived from a common C3 ancestor protein.
眼镜蛇毒因子（CVF，眼镜蛇毒中的补体激活蛋白）与第三补体成分的活化形式C3b之间的功能相似性，促使我们对源自两个系统发育距离较远物种的这两种蛋白质的结构特性进行比较分析。我们对CVF、人C3及其生理裂解产物C3b和C3c进行了各种生化分析。我们在此报告这些蛋白质的结构相似性，包括氨基酸组成、远紫外和近紫外圆二色光谱、二级结构、等电聚焦的条带模式和pI值、免疫化学交叉反应性、超微结构形态以及氨基末端氨基酸序列的相似性。对这些数据的分析表明，在结构上，CVF与C3c的相似性超过C3b。我们得出结论，CVF不是趋同进化的产物，而极有可能源自共同的C3祖先蛋白。
