Complement C1q subcomponent subunit A (C1QA)
The protein contains 245 amino acids for an estimated molecular weight of 26017 Da.
C1q associates with the proenzymes C1r and C1s to yield C1, the first component of the serum complement system. The collagen-like regions of C1q interact with the Ca(2+)-dependent C1r(2)C1s(2) proenzyme complex, and 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. (updated: Oct. 10, 2018)
Protein identification was indicated in the following studies:
Methods
The following articles were analysed to gather the proteome content of erythrocytes.
The gene or protein list provided in the studies were processed using the ID mapping API of Uniprot in September 2018. The number of proteins identified and mapped without ambiguity in these studies is indicated below.
Only Swiss-Prot entries (reviewed) were considered for protein evidence assignation.
| Publication | Identification 1 | Uniprot mapping 2 | Not mapped / Obsolete | TrEMBL | Swiss-Prot |
|---|---|---|---|---|---|
| Goodman (2013) | 2289 (gene list) | 2278 | 53 | 20599 | 2269 |
| Lange (2014) | 1234 | 1234 | 7 | 28 | 1224 |
| Hegedus (2015) | 2638 | 2622 | 0 | 235 | 2387 |
| Wilson (2016) | 1658 | 1528 | 170 | 291 | 1068 |
| d'Alessandro (2017) | 1826 | 1817 | 2 | 0 | 1815 |
| Bryk (2017) | 2090 | 2060 | 10 | 108 | 1942 |
| Chu (2018) | 1853 | 1804 | 55 | 362 | 1387 |
1 as available in the article and/or in supplementary material
2 uniprot mapping returns all protein isoforms as one entry
The compilation of older studies can be retrieved from the Red Blood Cell Collection database.
The data and differentiation stages presented below come from the proteomic study and analysis performed by our partners of the GReX consortium, more details are available in their published work.
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| Variant | Description |
|---|---|
| dbSNP:rs17887074 |
Biological Process
Aging
Astrocyte activation
Cell-cell signaling
Complement activation
Complement activation, classical pathway
Complement-mediated synapse pruning
Innate immune response
Microglial cell activation
Neuron remodeling
Positive regulation of astrocyte activation
Positive regulation of microglial cell activation
Positive regulation of neuron death
Regulation of complement activation
Response to iron ion
Synapse organization
Synapse pruning
Vertebrate eye-specific patterning
Viral process
The reference OMIM entry for this protein is 120550
Complement component 1, q subcomponent, a chain; c1qa
Complement component 1, q subcomponent, alpha polypeptide
Complement component c1q, a chain
Serum c1q
DESCRIPTION
The first component of complement is a calcium-dependent complex of the 3 subcomponents C1q, C1r (613785), and C1s (120580). Subcomponent C1q binds to immunoglobulin complexes with resulting serial activation of C1r (enzyme), C1s (proenzyme), and the other 8 components of complement. C1q is composed of 3 different species of chains, called A, B (C1QB; 120570), and C (C1QC; 120575). For a review of the complement system and its components, see Degn et al. (2011).CLONING
Reid (1974) reported a partial amino acid sequence of 95 residues of the 191 residues in the oxidized A chain of human subcomponent C1q. This region of the A chain contains a repeating sequence of glycine-X-Y, where X is often proline and Y is often hydroxyproline, for 78 residues. The 5 hydroxylysine residues and 5 hydroxyproline residues in the oxidized A chain are all in these 78 residues and only in the Y position of the repeating sequence. Prolonged collagenase digestion of the oxidized A chain yielded a large, apparently C-terminal peptide containing most of the noncollagenous sequences present in the chain. Reid (1974) concluded that the A chain of C1q contains a collagen-like region that constitutes most of the N-terminal half of the chain. Hedge et al. (1987) isolated a cDNA clone for the A chain of C1q from a human monocyte cDNA library using a variety of synthetic oligonucleotides as probes.GENE FUNCTION
Bing et al. (1982) showed that fibronectin (see 135600) binds to C1q in the same manner that it binds collagen. A major function of fibronectins is in adhesion of cells to extracellular materials, such as solid substrata and matrices. Because fibronectin stimulates endocytosis and promotes clearance of particulate material from circulation, the results of Bing et al. (1982) suggest that fibronectin functions in clearance of C1q-coated material, such as immune complexes or cellular debris. Diebolder et al. (2014) found that specific noncovalent interactions between Fc segments of IgG antibodies resulted in the formation of ordered antibody hexamers after antigen binding on cells. These hexamers recruited and activated C1, the first component of complement, thereby triggering the complement cascade. The interactions between neighboring Fc segments could be manipulated to block, reconstitute, and enhance complement activation and killing of target cells, using all 4 human IgG subclasses. Diebolder et al. (2014) offered a general model for understanding antibody-mediated complement activation and the design of antibody therapeutics with enhanced efficacy.MAPPING
By somatic cell hybrid analysis, Hedge et al. (1987) assigned the gene for the A chain of C1q to chromosome 1p, where the gene for the B chain had been assigned previously. The genes for the A, B, and C chains of C1q are tandemly arranged 5-prime to 3-prime in the order A-C-B on a 24-kb stretch of DNA (Sellar et al., 1991). A and C are separated by 4 kb and B and C are separated by 11 kb. Hybridization of cDNA probes to a hybrid cell line containing the derived X chromosome from an X;1(q21.2;p34) translocation described in a female patient with Duchenne muscular dystrophy (Lindenbaum et al., 1979; Boyd et al., 1988) showed that the A and B genes are located in the region 1p36.3-p34.1 (Sellar et al., 1992).MOLECULAR GENETICS
In patients with C1q deficiency (613652), Topaloglu et al. (1996) and Petry et al. (1997) identified the same homoz ... More on the omim web site
Oct. 19, 2018: Protein entry updated
Automatic update: OMIM entry 120550 was added.
Oct. 19, 2018: Additional information
Initial protein addition to the database. This entry was referenced in Bryk and co-workers. (2017).