C1q β-polypeptide deficiency

Gene Information


HUGO name: C1QB


  • Complement component 1, q subcomponent, beta polypeptide
  • Complement C1q subcomponent, B 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. 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 glycans consist of glc-gal disaccharides.

Structures (PDB)


Collagen-like domain: 29-112

    C1Q domain: 113-251

      Other features

      Signal peptide: 1-25

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

          Other related resourses:


          Expression pattern for human

          Tissue Expression (%) Clones
          well-differentiated invasive carcinoma, floor of mouth 46.05 1:100
          thymus 10.26 1:449
          head/neck 8.82 1:522
          nasopharynx 7.13 1:646
          subchondral bone 3.46 1:1332
          pheochromocytoma 2.95 1:1560
          mixed 2.14 28:60341
          spleen 1.91 3:7229
          rpe and choroid 1.74 4:10565
          lung, 2 pooled neuroendocrine lung carcinoids 1.67 6:16549

          Animal models



          C. elegans