C4 binding protein α deficiency

Gene Information


HUGO name: C4BPA


  • C4BP
  • complement component 4 binding protein, alpha
  • complement component 4-binding protein, alpha
  • C4b-binding protein alpha chain precursor
  • Proline-rich protein
  • PRP


Reference sequences

Chromosomal location


Protein Information


Protein function:

C4BP controls the classical pathway of complement activation. It binds as a cofactor to C3b/C4b inactivator (C3bina), which then hydrolyzes the complement fragment C4b. It also accelerates the degradation of the C4bc2a complex (C3 convertase) by dissociating the complement fragment C2a. Alpha chain binds C4b. It interacts also with anticoagulant protein S and with serum amyloid P component.


Disulfide-linked complex of C4bp alpha and beta chains of 3 possible sorts: a 570 kda complex of 7 alpha chains and 1 beta chain, a 530 kda homoheptamer of alpha chains or a 500 kda complex of 6 alpha chains and 1 beta chain. The central body of the alpha chain homopolymer supports tentacles, each with the binding site for C4b at the end.


It is uncertain whether MET-1 or MET-17 is the initiator.

Structures (PDB)


Sushi 1 domain: 49-109

    Sushi 2 domain: 112-171

      Sushi 3 domain: 174-235

        Sushi 4 domain: 238-295

          Sushi 5 domain: 298-361

            Sushi 6 domain: 364-423

              Sushi 7 domain: 425-481

                Sushi 8 domain: 483-539

                  Other features

                  Signal peptide: 1-48

                    C4b-binding protein alpha chain: 49-597

                      Other related resourses:


                      Expression pattern for human

                      Tissue Expression (%) Clones
                      uterus, endometrium 29.36 2:1790
                      nose, olfactory epithelium 23.55 1:1116
                      corresponding non cancerous liver tissue 11.34 6:13909
                      liver 6.06 6:26031
                      hepatocellular carcinoma 5.54 3:14226
                      lung, 2 pooled neuroendocrine lung carcinoids 4.76 3:16549
                      pool, liver+spleen 4.29 10:61327
                      human lung epithelial cell lines untreated lps 6hr to lps 4.19 1:6278
                      lung metatastic chondrosarcoma 4.08 1:6448
                      human skeletal muscle 2.45 1:10746

                      Animal models



                      C. elegans