- C1Q complex
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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, it is thought, 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 400kDa 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
It is assumed that the globular ends are the sites for multivalent attachment to the complement fixing sites in immune complexed immunoglobulin. Patients suffering from Lupus erythematosus often have deficient expression of C1q.
External links
Proteins: complement system (C, L, A) Activators/enzymes EarlyMiddleLateInhibitors Complement receptors Categories:- Genes on chromosome 1
- Chromosome 1 gene stubs
- Complement system
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