C1Q complex

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complement component 1, q subcomponent, A chain
Identifiers
Symbol	C1QA
HUGO	1241
Entrez	712
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
HUGO	1242
Entrez	713
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 C1QG
HUGO	1245
Entrez	714
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.

[edit] Structure

C1q is a 400K(K=1000) 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.

[edit] Function

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

[edit] External links

• MeSH Complement+C1q