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Gene Review

C1ra  -  complement component 1, r subcomponent A

Mus musculus

Synonyms: AI132558, C1r, Complement C1r-A subcomponent, Complement component 1 subcomponent r-A, mC1rA
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Disease relevance of C1r

  • We have expressed a truncated fragment of C1r protein without the N-terminal hydrophobic sequence in Escherichia coli and generated a polyclonal antibody against it [1].
  • FUT-175 also inhibited complement-mediated hemolysis, including both classical and alternative pathways, sites of inhibition being on C1r and C1s as evidenced by the intermediate-cell technique [2].

High impact information on C1r

  • This similarity extends to the serine protease component, which shares a similar modular construction and about 40% sequence identity with the C1r and C1s subcomponents of C1 [3].
  • Although homology in the amino acid sequence of P100 with that of human C1r and C1s subcomponents of C was less than 40%, a striking similarity in domain organization was found among these proteins, indicating that P100 is a new C4-activating serine protease structurally similar to C1r and C1s [4].
  • C1-Inh, which probably binds to C1r through the open end of the C1 cone, is too long asymmetric to be included within the cage [5].
  • One of these showed significant sequence homology with human complement C1r precursor [1].
  • Assignment of the complement serine protease genes C1r and C1s to chromosome 12 region 12p13 [6].

Biological context of C1r

  • The C1r and C1s loci also provide useful polymorphic DNA markers for the short arm of chromosome 12 [6].
  • Recent comparisons indicate a significant degree of sequence similarity between C1r and C1s and support the hypothesis that they are related by gene duplication [6].
  • The open reading frame of full-length cDNA clones encodes a pre-protein with a calculated molecular mass of 50.6 kDa which, except for an internal deletion of several modules, has a modular organization similar to that of C1r and shows 51% overall amino acid identity to corresponding regions of C1rA [7].
  • This review will initially summarize current information on the structure and function of C1r, with particular emphasis on the three-dimensional structure of its catalytic domain, which provides new insights into the activation mechanism of C1 [8].
  • C1r and C1s are highly specific serine proteases that initiate the classical pathway of complement activation [7].

Associations of C1r with chemical compounds

  • C1r and C1s are the serine proteases that form the catalytic unit of the C1 complex, the first component of complement [9].
  • A 100-kDa protein in the C4-activating component of Ra-reactive factor is a new serine protease having module organization similar to C1r and C1s [4].


  1. Identification of cDNA encoding a serine protease homologous to human complement C1r precursor from grafted mouse skin. Byun, S.J., Bahk, Y.Y., Ryoo, Z.Y., Kim, K.E., Hwang, H.Y., Lee, J.W., Yi, J.Y., Kim, T.Y. J. Invest. Dermatol. (2001) [Pubmed]
  2. Pharmacological studies of FUT-175, nafamstat mesilate. I. Inhibition of protease activity in in vitro and in vivo experiments. Aoyama, T., Ino, Y., Ozeki, M., Oda, M., Sato, T., Koshiyama, Y., Suzuki, S., Fujita, M. Jpn. J. Pharmacol. (1984) [Pubmed]
  3. Substrate specificities of the protease of mouse serum Ra-reactive factor. Ogata, R.T., Low, P.J., Kawakami, M. J. Immunol. (1995) [Pubmed]
  4. A 100-kDa protein in the C4-activating component of Ra-reactive factor is a new serine protease having module organization similar to C1r and C1s. Takayama, Y., Takada, F., Takahashi, A., Kawakami, M. J. Immunol. (1994) [Pubmed]
  5. Activation of the first component of human complement, C1, by monoclonal antibodies directed against different domains of subcomponent C1q. Kilchherr, E., Schumaker, V.N., Phillips, M.L., Curtiss, L.K. J. Immunol. (1986) [Pubmed]
  6. Assignment of the complement serine protease genes C1r and C1s to chromosome 12 region 12p13. Nguyen, V.C., Tosi, M., Gross, M.S., Cohen-Haguenauer, O., Jegou-Foubert, C., de Tand, M.F., Meo, T., Frézal, J. Hum. Genet. (1988) [Pubmed]
  7. A novel murine complement-related gene encoding a C1r-like serum protein. Circolo, A., Garnier, G., Volanakis, J.E. Mol. Immunol. (2003) [Pubmed]
  8. Structure, function and molecular genetics of human and murine C1r. Arlaud, G.J., Gaboriaud, C., Garnier, G., Circolo, A., Thielens, N.M., Budayova-Spano, M., Fontecilla-Camps, J.C., Volanakis, J.E. Immunobiology (2002) [Pubmed]
  9. Complement C1r and C1s genes are duplicated in the mouse: differential expression generates alternative isomorphs in the liver and in the male reproductive system. Garnier, G., Circolo, A., Xu, Y., Volanakis, J.E. Biochem. J. (2003) [Pubmed]
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