C1QA explained

Complement C1q subcomponent subunit A is a protein that in humans is encoded by the C1QA gene.^[1]

This gene encodes a major constituent of the human complement system subcomponent C1q. C1q associates with C1r and C1s in order to yield the first component of the serum complement system. Deficiency of C1q has been associated with lupus erythematosus and glomerulonephritis. C1q is composed of 18 polypeptide chains: six A-chains, six B-chains, and six C-chains. Each chain contains a collagen-like region located near the N terminus and a C-terminal globular region. The A-, B-, and C-chains are arranged in the order A-C-B on chromosome 1. This gene encodes the A-chain polypeptide of human complement subcomponent C1q.^[2]

Further reading

• Petry F . Molecular basis of hereditary C1q deficiency. . Immunobiology . 199 . 2 . 286–94 . 1999 . 9777412 . 10.1016/s0171-2985(98)80033-8.
• Thielens NM, Tacnet-Delorme P, Arlaud GJ . Interaction of C1q and mannan-binding lectin with viruses. . Immunobiology . 205 . 4–5 . 563–74 . 2003 . 12396016 . 10.1078/0171-2985-00155 .
• Reid KB . Isolation, by partial pepsin digestion, of the three collagen-like regions present in subcomponent Clq of the first component of human complement . Biochem. J. . 155 . 1 . 5–17 . 1976 . 10.1042/bj1550005 . 7240 . 1172796 .
• Reid KB . Complete amino acid sequences of the three collagen-like regions present in subcomponent C1q of the first component of human complement . Biochem. J. . 179 . 2 . 367–71 . 1979 . 10.1042/bj1790367 . 486087 . 1186634 .
• Krumdieck R, Höök M, Rosenberg LC, Volanakis JE . The proteoglycan decorin binds C1q and inhibits the activity of the C1 complex . J. Immunol. . 149 . 11 . 3695–701 . 1992 . 10.4049/jimmunol.149.11.3695 . 1431141 . free .
• Sellar GC, Blake DJ, Reid KB . Characterization and organization of the genes encoding the A-, B- and C-chains of human complement subcomponent C1q. The complete derived amino acid sequence of human C1q . Biochem. J. . 274 . 2. 481–90 . 1991 . 1706597 . 10.1042/bj2740481. 1150164 .
• Ebenbichler CF, Thielens NM, Vornhagen R . Human immunodeficiency virus type 1 activates the classical pathway of complement by direct C1 binding through specific sites in the transmembrane glycoprotein gp41 . J. Exp. Med. . 174 . 6 . 1417–24 . 1992 . 1744579 . 10.1084/jem.174.6.1417 . 2119058 . etal.
• Su H, Boackle RJ . Interaction of the envelope glycoprotein of human immunodeficiency virus with C1q and fibronectin under conditions present in human saliva . Mol. Immunol. . 28 . 8 . 811–7 . 1991 . 1875953 . 10.1016/0161-5890(91)90044-K .
• Busby TF, Ingham KC . NH2-terminal calcium-binding domain of human complement C1s- mediates the interaction of C1r- with C1q . Biochemistry . 29 . 19 . 4613–8 . 1990 . 2372546 . 10.1021/bi00471a016 .
• Bing DH, Almeda S, Isliker H . Fibronectin binds to the C1q component of complement . Proc. Natl. Acad. Sci. U.S.A. . 79 . 13 . 4198–201 . 1982 . 6981115 . 10.1073/pnas.79.13.4198 . 346605 . 1982PNAS...79.4198B . etal. free .
• Reid KB, Gagnon J, Frampton J . Completion of the amino acid sequences of the A and B chains of subcomponent C1q of the first component of human complement . Biochem. J. . 203 . 3 . 559–69 . 1982 . 10.1042/bj2030559 . 6981411 . 1158269 .
• Stoiber H, Thielens NM, Ebenbichler C . The envelope glycoprotein of HIV-1 gp120 and human complement protein C1q bind to the same peptides derived from three different regions of gp41, the transmembrane glycoprotein of HIV-1, and share antigenic homology . Eur. J. Immunol. . 24 . 2 . 294–300 . 1994 . 7507842 . 10.1002/eji.1830240203 . 24908489 . etal.
• Prohászka Z, Hidvégi T, Ujhelyi E . Interaction of complement and specific antibodies with the external glycoprotein 120 of HIV-1 . Immunology . 85 . 2 . 184–9 . 1995 . 7642209 . 1383879 . etal.
• Stoiber H, Ebenbichler CF, Thielens NM . HIV-1 rsgp41 depends on calcium for binding of human c1q but not for binding of gp120 . Mol. Immunol. . 32 . 5 . 371–4 . 1995 . 7739575 . 10.1016/0161-5890(94)00156-U . etal.
• Gulati P, Guc D, Lemercier C . Expression of the components and regulatory proteins of the classical pathway of complement in normal and diseased synovium . Rheumatol. Int. . 14 . 1 . 13–9 . 1994 . 7939135 . 10.1007/BF00302666 . 2144366 . etal.
• Gulati P, Lemercier C, Guc D . Regulation of the synthesis of C1 subcomponents and C1-inhibitor . Behring Inst. Mitt. . 93 . 196–203 . 1994 . 8172568 . etal.
• Ghebrehiwet B, Lim BL, Peerschke EI . Isolation, cDNA cloning, and overexpression of a 33-kD cell surface glycoprotein that binds to the globular "heads" of C1q . J. Exp. Med. . 179 . 6 . 1809–21 . 1994 . 8195709 . 10.1084/jem.179.6.1809 . 2191527 . etal.
• Thielens NM, Bally IM, Ebenbichler CF . Further characterization of the interaction between the C1q subcomponent of human C1 and the transmembrane envelope glycoprotein gp41 of HIV-1 . J. Immunol. . 151 . 11 . 6583–92 . 1994 . 10.4049/jimmunol.151.11.6583 . 8245486 . etal. free .
• Hidvégi T, Prohászka Z, Ujhelyi E . Studies on the mechanism of complement-mediated inhibition of antibody binding to HIV gp41 . Clin. Exp. Immunol. . 94 . 3 . 490–3 . 1994 . 8252810 . 10.1111/j.1365-2249.1993.tb08223.x. 1534428 . etal.

Notes and References

1. Sellar GC, Cockburn D, Reid KB . Localization of the gene cluster encoding the A, B, and C chains of human C1q to 1p34.1-1p36.3 . Immunogenetics . 35 . 3 . 214–6 . Mar 1992 . 1537612 . 10.1007/bf00185116. 26894430 .
2. Web site: Entrez Gene: C1QA complement component 1, q subcomponent, A chain.