Complement component 2

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Protein C2 PDB 2i6q.png
Available structures
PDB Ortholog search: PDBe RCSB
Aliases C2, ARMD14, CO2, complement component 2, complement C2
External IDs MGI: 88226 HomoloGene: 45 GeneCards: C2
Gene location (Human)
Chromosome 6 (human)
Chr. Chromosome 6 (human)[1]
Chromosome 6 (human)
Genomic location for C2
Genomic location for C2
Band 6p21.33 Start 31,897,785 bp[1]
End 31,945,672 bp[1]
RNA expression pattern
PBB GE C2 203052 at fs.png
More reference expression data
Species Human Mouse
RefSeq (mRNA)


RefSeq (protein)


Location (UCSC) Chr 6: 31.9 – 31.95 Mb Chr 17: 34.86 – 34.9 Mb
PubMed search [3] [4]
View/Edit Human View/Edit Mouse

Complement C2 is a protein that in humans is encoded by the C2 gene.[5] The protein encoded by this gene is part of the classical pathway of the complement system, acting as a multi-domain serine protease. Deficiency of C2 has been associated with certain autoimmune diseases.[5]


In the classical and lectin pathways of complement activation, formation of the C3-convertase and C5-convertases requires binding of C2 to an activated surface-bound C4b in the presence of Mg2+; the resultant C4bC2 complex is then cleaved by C1s or MASP2 into C2a and C2b. It is thought that cleavage of C2 by C1s, while bound to C4b, results in a conformational rotation of C2b whereas the released C2a fragment may retain most of its original structure.

C2a is the larger, enzymatically active fragment which is incorporated into the C3 convertase in this pathway, C4b2a (NB: some sources now refer to the larger fragment of C2 as C2b, making the C3 convertase C4b2b). The smaller fragment, C2b (or C2a, depending on your source) is released into the fluid phase.[6]


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