Complement component C2 is necessary for the formation of C3 convertase, the key enzyme of the classical pathway of complement activation. The single gene encoding C2 has been mapped within the major histocompatibility complex class III cluster of genes on the short arm of human chromosome 6, 421 bp telomeric of the gene encoding the structural and functional homolog of complement component C2 in the alternative pathway, complement factor B.
Studies on the expression of these related genes using primary hepatocyte cultures and monocytes stimulated by interleukin-1 and interferon -γ have indicated that they are transcriptionally regulated. However, stimulation of human mononuclear phagocytes by lipid A induced an increase in C2 mRNA without a net increase in complement C2 secretion,suggesting that post-transcriptional mechanisms may also be involved in regulating C2 gene expression.
Complement C2 shares homology with the classical serine proteinases, but is unusual in having a catalytic chain with a much extended N-terminus. Activation of the complement cascade triggers a number of biological effects that assist the clearance of immune complexes from the blood, including opsonization of particles, release of inflammatory peptides and lysis of cellular antigens.
Structural analysis of complement C2 has been hampered by the low concentration of the protein in plasma, and by its susceptibility to proteolysis during isolation, but sufficient amino acid sequence data were obtained to permit the use of mixed oligodeoxyribonucleotide probes to identify partial cDNA clones.
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2. Woods D E, et al. (1984). Isolation of a complementary DNA clone for the human complement protein C2 and its use in the identification of a restriction fragment length polymorphism. Journal of Clinical Investigation, 74(2), 634.