Title : Human complement component C3: cDNA coding
sequence and derived primary structure
Abstract :
- The complete cDNA coding sequence and derived amino acid sequence of human complement component C3 are presented
- The encoded precursor molecule contains a signal peptide of 22 amino acid residues , the beta chain (645 residues ), and the alpha chain (992 residues )
- The two chains are joined by four arginine residues not present in the mature protein
- Several functionally important sites have been localized, such as the thiolester site , the cleavage site liberating the anaphylatoxin, and two sites of cleavage by the serine protease factor I , as well as a peptide fragment with leukocyte mobilizing activity
- At least two carbohydrate attachment sites , one on each chain, have been identified
- Human C3 has 79% identity to mouse C3 at the nucleotide level and 77% identity at the amino acid level
- The protease alpha 2-macroglobulin and complement component C4 show considerable homology to C3, suggesting that the three proteins have evolved from a common ancestor