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PROSITE documentation PDOC00857C1q domain profile
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PURL: https://purl.expasy.org/prosite/documentation/PDOC00857
C1q is a subunit of the C1 enzyme complex that activates the serum complement system. It is composed of 9 disulfide-linked dimers of the chains A, B and C, which share a common structure which consist of a N-terminal nonhelical region, a triple helical (collagenous) region and a C-terminal globular head which is called the C1q domain. That domain consists of about 136 amino acids and has been found in the C-terminus of vertebrate secreted or membrane-bound proteins which are mostly short-chain collagens and collagen-like molecules [1,2,3,4]. These proteins are listed below:
- Complement C1q subcomponent chains A, B and C. 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.
- Vertebrate short-chain collagen type VIII, the major component of the basement membrane of corneal endothelial cells. It is composed of a triple helical domain in between a short N-terminal and a larger C-terminal globule which contains the C1q domain.
- Vertebrate collagen type X, which has the same structure than collagen type VIII. It is a product of hyperthrophic chondrotocytes.
- Bluegill inner-ear specific structural protein. This short-chain collagen forms a microstructural matrix within the otolithic membrane.
- Chipmunk hibernation-associated plasma proteins HP-20, HP-25 and HP-27. These proteins disappear from blood specifically during hibernation. They contain a collagen-like domain near the N-terminus and a C-terminal C1q domain.
- Human precerebellin, which is located within postsynaptic structures of Purkinje cells, probably membrane-bound. Cerebellin is involved in synaptic activity.
- Rat precerebellin-like glycoprotein, a probable membrane protein. The C1q domain is located at the C-terminal extracellular extremity.
- Human endothelial cell multimerin (ECM), a carrier protein for platelet factor V/VA.
- Vertebrate 30 Kd adipocyte complement-related protein (ACRP30), also known as ApM1 or AdipoQ.
- Vertebrate myonectin (CTRP15), a nutrient responsive myokine secreted by skeletal muscle to regulate whole-body fatty acid metabolism [5].
The C-terminal globular domain of the C1q subcomponents and collagen types VIII and X is important both for the correct folding and alignment of the triple helix and for protein-protein recognition events [6,7]. For collagen type X it has been suggested that the domain is important for initiation and maintenance of the correct assembly of the protein [8]. The globular head is a trimer of C1q domains. Each individual C1q adopts a 10-strand Jelly-roll fold arranged in two antiparallel 5-stranded β-sheets (see <PDB:4F3J>) [9]. There are two well conserved regions within the C1q domain: an aromatic motif is located within the first half of the domain, the other conserved region is located near the C-terminal extremity.
Expert(s) to contact by email:Reid K.B.M.;
Last update:March 2013 / Profile and text revised.
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PROSITE method (with tools and information) covered by this documentation:
| 1 | Authors | Smith K.F. Haris P.I. Chapman D. Reid K.B.M. Perkins S.J. |
| Title | Beta-sheet secondary structure of the trimeric globular domain of C1q of complement and collagen types VIII and X by Fourier-transform infrared spectroscopy and averaged structure predictions. | |
| Source | Biochem. J. 301:249-256(1994). | |
| PubMed ID | 8037678 |
| 2 | Authors | Brass A. Kadler K.E. Thomas J.T. Grant M.E. Boot-Handford R.P. |
| Title | The fibrillar collagens, collagen VIII, collagen X and the C1q complement proteins share a similar domain in their C-terminal non-collagenous regions. | |
| Source | FEBS Lett. 303:126-128(1992). | |
| PubMed ID | 1607009 |
| 3 | Authors | Petry F. Reid K.B.M. Loos M. |
| Title | Isolation, sequence analysis and characterization of cDNA clones coding for the C chain of mouse C1q. Sequence similarity of complement subcomponent C1q, collagen type VIII and type X and precerebellin. | |
| Source | Eur. J. Biochem. 209:129-134(1992). | |
| PubMed ID | 1396691 |
| 4 | Authors | Bork P. |
| Source | Unpublished observations (1995). |
| 5 | Authors | Seldin M.M. Peterson J.M. Byerly M.S. Wei Z. Wong G.W. |
| Title | Myonectin (CTRP15), a novel myokine that links skeletal muscle to systemic lipid homeostasis. | |
| Source | J. Biol. Chem. 287:11968-11980(2012). | |
| PubMed ID | 22351773 | |
| DOI | 10.1074/jbc.M111.336834 |
| 6 | Authors | Rosenbloom J. Endo R. Harsch M. |
| Source | J. Biol. Chem. 251:2070-2076(1976). |
| 7 | Authors | Engel J. Prockop D.J. |
| Title | The zipper-like folding of collagen triple helices and the effects of mutations that disrupt the zipper. | |
| Source | Annu. Rev. Biophys. Biophys. Chem. 20:137-152(1991). | |
| PubMed ID | 1867713 |
| 8 | Authors | Kwan A.P.L. Cummings C.E. Chapman J.A. Grant M.E. |
| Title | Macromolecular organization of chicken type X collagen in vitro. | |
| Source | J. Cell Biol. 114:597-604(1991). | |
| PubMed ID | 1860888 |
| 9 | Authors | Tu X. Palczewski K. |
| Title | Crystal structure of the globular domain of C1QTNF5: Implications for late-onset retinal macular degeneration. | |
| Source | J. Struct. Biol. 180:439-446(2012). | |
| PubMed ID | 22892318 | |
| DOI | 10.1016/j.jsb.2012.07.011 |
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