Biology:Complement component 4B

Generic protein structure example

Complement component 4B (Chido blood group) is a protein that in humans is encoded by the C4B gene.

This gene encodes the basic form of complement factor 4, part of the classical activation pathway. The protein is expressed as a single chain precursor which is proteolytically cleaved into a trimer of alpha, beta, and gamma chains prior to secretion. The trimer provides a surface for interaction between the antigen-antibody complex and other complement components. The alpha chain may be cleaved to release C4 anaphylatoxin, a mediator of local inflammation. Deficiency of this protein is associated with systemic lupus erythematosus. This gene localizes to the major histocompatibility complex (MHC) class III region on chromosome 6. Varying haplotypes of this gene cluster exist, such that individuals may have 1, 2, or 3 copies of this gene. In addition, this gene exists as a long form and a short form due to the presence or absence of a 6.4 kb endogenous HERV-K retrovirus in intron 9. [provided by RefSeq, Jul 2008].

See also

• Complement component 4
  • Complement component 4A
• HLA A1-B8-DR3-DQ2 haplotype
• Complement system
• Complement deficiency

Further reading

• "Molecular genetics of the human MHC complement gene cluster". Experimental and Clinical Immunogenetics 15 (4): 213–30. 1998. doi:10.1159/000019075. PMID 10072631. 
• "Modular variations of the human major histocompatibility complex class III genes for serine/threonine kinase RP, complement component C4, steroid 21-hydroxylase CYP21, and tenascin TNX (the RCCX module). A mechanism for gene deletions and disease associations". The Journal of Biological Chemistry 274 (17): 12147–56. Apr 1999. doi:10.1074/jbc.274.17.12147. PMID 10207042. 
• "A cluster of positively charged amino acids in the C4BP alpha-chain is crucial for C4b binding and factor I cofactor function". The Journal of Biological Chemistry 274 (27): 19237–45. Jul 1999. doi:10.1074/jbc.274.27.19237. PMID 10383431. 
• "C1q and C4b bind simultaneously to CR1 and additively support erythrocyte adhesion". Journal of Immunology 163 (9): 5056–63. Nov 1999. PMID 10528211. 
• "Elongation factor-1alpha as a homologous complement activator of Jurkat cells". International Journal of Molecular Medicine 6 (1): 87–92. Jul 2000. doi:10.3892/ijmm.6.1.87. PMID 10851272. 
• "Genetic polymorphism of C4 in man and localisation of a structural C4 locus to the HLA gene complex of chromosome 6". Nature 264 (5583): 253–4. Nov 1976. doi:10.1038/264253a0. PMID 1088823. 
• "Two clusters of acidic amino acids near the NH2 terminus of complement component C4 alpha'-chain are important for C2 binding". Journal of Immunology 165 (5): 2518–27. Sep 2000. doi:10.4049/jimmunol.165.5.2518. PMID 10946278. 
• "Frequencies of certain complement protein alleles and serum levels of anti-heat-shock protein antibodies in cerebrovascular diseases". Stroke: A Journal of Cerebral Circulation 31 (11): 2648–52. Nov 2000. doi:10.1161/01.STR.31.11.2648. PMID 11062289. 
• "Lack of evidence of a specific role for C4A gene deficiency in determining disease susceptibility among C4-deficient patients with systemic lupus erythematosus (SLE)". Clinical and Experimental Immunology 123 (1): 133–9. Jan 2001. doi:10.1046/j.1365-2249.2001.01438.x. PMID 11168010. 
• "Complement C4bC2 complex formation: an investigation by surface plasmon resonance". Biochimica et Biophysica Acta (BBA) - Protein Structure and Molecular Enzymology 1544 (1–2): 96–112. Jan 2001. doi:10.1016/S0167-4838(00)00208-9. PMID 11341920.