C1Q complex

Jump to: navigation, search
complement component 1, q subcomponent, A chain
Identifiers
SymbolC1QA
Entrez712
HUGO1241
OMIM120550
RefSeqNM_015991
UniProtP02745
Other data
LocusChr. 1 p36.3-34.1
complement component 1, q subcomponent, B chain
Identifiers
SymbolC1QB
Entrez713
HUGO1242
OMIM120570
RefSeqNM_000491
UniProtP02746
Other data
LocusChr. 1 p36.3-34.1
complement component 1, q subcomponent, C chain
Identifiers
SymbolC1QC
Alt. symbolsC1QG
Entrez714
HUGO1245
OMIM120575
RefSeqNM_172369
UniProtP02747
Other data
LocusChr. 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 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 C1 protein, showing subunits C1r, C1s, and the C1q tails.

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




Linked-in.jpg