title: Cobra venom factor: structural homology with the third component of human complement.
abstract: 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.
mesh_terms: D000595:Amino Acid Sequence; D000596:Amino Acids / Q000032:analysis; D002942:Circular Dichroism; D003176:Complement C3 / Q000032:analysis / Q000276:immunology; D003179:Complement C3b / Q000032:analysis; D015932:Complement C3c; D003429:Cross Reactions; D004546:Elapid Venoms / Q000032:analysis / Q000276:immunology; D006801:Humans; D007525:Isoelectric Focusing; D008855:Microscopy, Electron, Scanning; D008970:Molecular Weight; D013438:Sulfhydryl Compounds / Q000032:analysis
chemical_list: D000596:Amino Acids; D003176:Complement C3; D004546:Elapid Venoms; D013438:Sulfhydryl Compounds; C016310:cobra venom factor; D003179:Complement C3b; D015932:Complement C3c