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C1Q complex: Wikis

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complement component 1, q subcomponent, A chain
Identifiers
Symbol C1QA
Entrez 712
HUGO 1241
OMIM 120550
RefSeq NM_015991
UniProt P02745
Other data
Locus Chr. 1 p36.3-34.1
complement component 1, q subcomponent, B chain
Identifiers
Symbol C1QB
Entrez 713
HUGO 1242
OMIM 120570
RefSeq NM_000491
UniProt P02746
Other data
Locus Chr. 1 p36.3-34.1
complement component 1, q subcomponent, C chain
Identifiers
Symbol C1QC
Alt. symbols C1QG
Entrez 714
HUGO 1245
OMIM 120575
RefSeq NM_172369
UniProt P02747
Other data
Locus Chr. 1 p36.11

The C1q complex is potentially multivalent for attachment to the complement fixation sites of immunoglobulin.

The sites are on the CH2 domain of IgG and probably on the CH4 domain of IgM.

The appropriate peptide sequence of the complement fixing site might become exposed following complexing of the immunoglobulin, or the sites might always be available, but might require multiple attachment by C1q with critical geometry in order to achieve the necessary avidity.

Structure

C1q is a 400 kDa(1 kDa=1000 Da) protein formed from 18 peptide chains in 3 subunits of 6. Each 6 peptide subunit consists of a Y-shaped pair of triple peptide helices joined at the stem and ending in a globular non-helical head.

The 80 amino-acid helical component of each triple peptide contain many Gly-X-Y sequences,where X and Y are proline, isoleucine or hydroxylysine; they therefore strongly resemble collagen fibrils.

Function

The classical and alternative complement pathways.

It is assumed that the globular ends are the sites for multivalent attachment to the complement fixing sites in immune complexed immunoglobulin.

External links

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