Complement C2 is a
protein
Proteins are large biomolecules and macromolecules that comprise one or more long chains of amino acid residues. Proteins perform a vast array of functions within organisms, including catalysing metabolic reactions, DNA replication, respo ...
that in humans is encoded by the ''C2''
gene
In biology, the word gene (from , ; "...Wilhelm Johannsen coined the word gene to describe the Mendelian units of heredity..." meaning ''generation'' or ''birth'' or ''gender'') can have several different meanings. The Mendelian gene is a ba ...
.
The protein encoded by this gene is part of the
classical pathway of the
complement system
The complement system, also known as complement cascade, is a part of the immune system that enhances (complements) the ability of antibodies and phagocytic cells to clear microbes and damaged cells from an organism, promote inflammation, and at ...
, acting as a multi-domain serine protease. Deficiency of C2 has been associated with certain autoimmune diseases.
Function
In the
classical and
lectin
Lectins are carbohydrate-binding proteins that are highly specific for sugar groups that are part of other molecules, so cause agglutination of particular cells or precipitation of glycoconjugates and polysaccharides. Lectins have a role in rec ...
pathways of
complement activation
The complement system, also known as complement cascade, is a part of the immune system that enhances (complements) the ability of antibodies and phagocytic
Phagocytosis () is the process by which a cell uses its plasma membrane to engulf a ...
, formation of the
C3-convertase
C3 convertase (''C4bC2b'', formerly ''C4b2a'') belongs to family of serine proteases and is necessary in innate immunity as a part of the complement system which eventuate in opsonisation of particles, release of inflammatory peptides, C5 conv ...
and
C5-convertase
C5 convertase is an enzyme belonging to a family of serine proteases that play key role in the innate immunity. It participates in the complement system ending with cell death.
There are four different C5 convertases able to specifically con ...
s requires binding of C2 to an activated surface-bound
C4b in the presence of
Mg2+; the resultant C4bC2 complex is cleaved by
C1s
Complement component 1s (, '' C1 esterase'', ''activated complement C1s'', ''complement C overbar 1r'', ''C1s'') is a protein involved in the complement system. C1s is part of the C1 complex. In humans, it is encoded by the ''C1S'' gene.
C1s cle ...
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.
C2b is the smallest , enzymatically active, fragment of C3 convertase in this pathway, C4b2b (NB:
some sources now refer to the larger fragment of C2 as C2b, making the C3 convertase C4b2b, whereas older sources refer to the larger fragment of C2 as C2a, making the C3 convertase C4b2a). The smaller fragment, C2a (or C2b, depending on the source) is released into the fluid phase.
References
Further reading
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External links
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Complement system
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