C1q α-polypeptide deficiency

Gene Information


HUGO name: C1QA


  • Complement component 1, q subcomponent, alpha polypeptide
  • Complement C1q subcomponent, A chain precursor


Reference sequences

Chromosomal location


Protein Information


Protein function:

C1q associates with the proenzymes C1r and C1s to yield C1, the first component of the serum complement system. The collagen-like regions of C1q interact with the Ca(2+)-dependent C1r(2)C1s(2) proenzyme complex, and efficient activation of C1 takes place on interaction of the globular heads of C1q with the Fc regions of IgG or IgM antibody present in immune complexes.


C1 is a calcium-dependent trimolecular complex of C1q, r and s in the molar ration of 1:2:2. The C1q subcomponent is composed of nine subunits, six of which are disulfide-linked dimers of the a and b chains, and three of which are disulfide-linked dimers of the c chain.

Post-translational modification:

O-linked glycan consists of glc-gal disaccharide.

Structures (PDB)


Collagen-like domain: 31-109

    C1q domain: 110-245

      Other features

      Signal peptide: 1-22

        Complement C1q subcomponent, a chain: 23-245

          Disulfide bond interchain (with c-29 in b chain): 26

            Other related resourses:


            Expression pattern for human

            Tissue Expression (%) Clones
            skin, melanocyte 16.46 1:520
            lung with fibrosis 11.57 2:1479
            esophagus 8.71 3:2949
            normal head/neck tissue 6.62 1:1292
            ovary, pooled 5.86 4:5846
            spleen 4.74 4:7229
            mixed 4.40 31:60341
            human eye anterior segment 4.33 1:1978
            germ cell 4.26 10:20077
            rpe and choroid 4.05 5:10565

            Animal models



            C. elegans