title: Chemical evidence for common genetic ancestry of complement components C3 and C5.
abstract: Sequence studies reveal a marked similarity between the partial primary structures of human C3a and C5a anaphylatoxins. Eight of the first 25 residues are identical when threonine at position 1 in C5a is aligned with glutamine at position 3 in C3a and one gap is inserted in the C3a sequence. A unique cysteinyl-cysteine sequence is conserved in the 2 molecules, which further suggests a genetic relatedness. Computer-generated alignment scores from comparison of the NH2-terminal portions of human C3a and C5a exceeded by 4 standard deviations the score from random permutations of these same sequences. This sequence similarity between the two anaphylatoxins suggests that the respective precursors, C3 and C5, had a common genetic ancestry. The proposed genetic relationship between C3 and C5 may express itself functionally through a similar molecular behavior in complement-dependent cytolysis.
mesh_terms: D000595:Amino Acid Sequence; D000596:Amino Acids / Q000032:analysis; D005075:Biological Evolution; D003176:Complement C3 / Q000096:biosynthesis; D003182:Complement C5 / Q000096:biosynthesis; D003165:Complement System Proteins / Q000096:biosynthesis; D006801:Humans; D014158:Transcription, Genetic
chemical_list: D000596:Amino Acids; D003176:Complement C3; D003182:Complement C5; D003165:Complement System Proteins