P02745 · C1QA_HUMAN
- ProteinComplement C1q subcomponent subunit A
- GeneC1QA
- StatusUniProtKB reviewed (Swiss-Prot)
- Organism
- Amino acids245 (go to sequence)
- Protein existenceEvidence at protein level
- Annotation score5/5
Function
function
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 Ca2+-dependent C1r2C1s2 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.
GO annotations
all annotations | all molecular function | virus receptor activity | dna binding | rna binding | cytoskeletal motor activity | catalytic activity | gtpase activity | structural molecule activity | transporter activity | cytoskeletal protein binding | lipid binding | cyclase activity | antioxidant activity | oxidoreductase activity | transferase activity | hydrolase activity | lyase activity | isomerase activity | ligase activity | protein tag activity | cargo receptor activity | histone binding | protein folding chaperone | translation regulator activity | nutrient reservoir activity | receptor ligand activity | molecular transducer activity | molecular adaptor activity | toxin activity | cell adhesion mediator activity | molecular function regulator activity | virus coreceptor activity | catalytic activity, acting on a protein | catalytic activity, acting on dna | catalytic activity, acting on rna | molecular carrier activity | transcription regulator activity | general transcription initiation factor activity | molecular sensor activity | molecular sequestering activity | atp-dependent activity | other molecular function | all biological process | mitotic cell cycle | cytokinesis | cytoplasmic translation | immune system process | muscle system process | circulatory system process | renal system process | respiratory system process | carbohydrate metabolic process | generation of precursor metabolites and energy | dna replication | dna repair | dna recombination | chromatin organization | dna-templated transcription | regulation of dna-templated transcription | trna metabolic process | protein folding | protein glycosylation | amino acid metabolic process | modified amino acid metabolic process | lipid metabolic process | vitamin metabolic process | sulfur compound metabolic process | intracellular protein transport | nucleocytoplasmic transport | autophagy | inflammatory response | mitochondrion organization | cytoskeleton organization | microtubule-based movement | peroxisome organization | lysosome organization | chromosome segregation | cell adhesion | establishment or maintenance of cell polarity | programmed cell death | photosynthesis | mrna metabolic process | snrna metabolic process | vesicle-mediated transport | reproductive process | digestive system process | signaling | cell differentiation | protein catabolic process | extracellular matrix organization | regulatory ncrna-mediated gene silencing | telomere organization | cell junction organization | wound healing | ribosome biogenesis | cilium organization | anatomical structure development | cell motility | nervous system process | endocrine process | protein maturation | transmembrane transport | nucleobase-containing small molecule metabolic process | hepaticobiliary system process | membrane organization | protein-containing complex assembly | cell wall organization or biogenesis | nitrogen cycle metabolic process | protein localization to plasma membrane | defense response to other organism | detoxification | meiotic nuclear division | mitotic nuclear division | mitochondrial gene expression | carbohydrate derivative metabolic process | other biological process | all cellular component | nuclear chromosome | extracellular region | extracellular space | cell wall | nucleus | nuclear envelope | nucleoplasm | chromosome | nucleolus | mitochondrion | lysosome | endosome | vacuole | peroxisome | endoplasmic reticulum | golgi apparatus | lipid droplet | microtubule organizing center | cytosol | ribosome | cytoskeleton | plasma membrane | cilium | plastid | thylakoid | external encapsulating structure | extracellular matrix | cytoplasmic vesicle | organelle | other cellular component | |||
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Aspect | Term | |
---|---|---|
Cellular Component | collagen trimer | |
Cellular Component | collagen-containing extracellular matrix | |
Cellular Component | complement component C1 complex | |
Cellular Component | complement component C1q complex | |
Cellular Component | extracellular region | |
Cellular Component | postsynapse | |
Cellular Component | synapse | |
Molecular Function | amyloid-beta binding | |
Biological Process | astrocyte activation | |
Biological Process | cell-cell signaling | |
Biological Process | complement activation | |
Biological Process | complement activation, classical pathway | |
Biological Process | complement-mediated synapse pruning | |
Biological Process | innate immune response | |
Biological Process | microglial cell activation | |
Biological Process | neuron remodeling | |
Biological Process | synapse organization | |
Biological Process | synapse pruning | |
Biological Process | vertebrate eye-specific patterning |
Keywords
- Biological process
Enzyme and pathway databases
Names & Taxonomy
Protein names
- Recommended nameComplement C1q subcomponent subunit A
Gene names
Organism names
- Organism
- Taxonomic lineageEukaryota > Metazoa > Chordata > Craniata > Vertebrata > Euteleostomi > Mammalia > Eutheria > Euarchontoglires > Primates > Haplorrhini > Catarrhini > Hominidae > Homo
Accessions
- Primary accessionP02745
- Secondary accessions
Proteomes
Organism-specific databases
Subcellular Location
Disease & Variants
Involvement in disease
C1q deficiency 1 (C1QD1)
- Note
- DescriptionAn autosomal recessive disorder caused by impaired activation of the complement classical pathway. It generally leads to severe immune complex disease characterized by recurrent skin lesions, chronic infections, an increased risk of systemic lupus erythematosus, and glomerulonephritis.
- See alsoMIM:613652
Features
Showing features for natural variant, mutagenesis.
Type | ID | Position(s) | Description | |||
---|---|---|---|---|---|---|
Natural variant | VAR_021090 | 23 | in dbSNP:rs17887074 | |||
Sequence: E → K | ||||||
Mutagenesis | 222 | Decreases binding to IgM and IgG. | ||||
Sequence: K → E |
Variants
We now provide the "Disease & Variants" viewer in its own tab.
The viewer provides 402 variants from UniProt as well as other sources including ClinVar and dbSNP.
Organism-specific databases
Miscellaneous
Chemistry
Genetic variation databases
PTM/Processing
Features
Showing features for signal, chain, disulfide bond, modified residue, glycosylation.
Type | ID | Position(s) | Description | |||
---|---|---|---|---|---|---|
Signal | 1-22 | |||||
Sequence: MEGPRGWLVLCVLAISLASMVT | ||||||
Chain | PRO_0000003517 | 23-245 | Complement C1q subcomponent subunit A | |||
Sequence: EDLCRAPDGKKGEAGRPGRRGRPGLKGEQGEPGAPGIRTGIQGLKGDQGEPGPSGNPGKVGYPGPSGPLGARGIPGIKGTKGSPGNIKDQPRPAFSAIRRNPPMGGNVVIFDTVITNQEEPYQNHSGRFVCTVPGYYYFTFQVLSQWEICLSIVSSSRGQVRRSLGFCDTTNKGLFQVVSGGMVLQLQQGDQVWVEKDPKKGHIYQGSEADSVFSGFLIFPSA | ||||||
Disulfide bond | 26 | Interchain (with C-29 in B chain) | ||||
Sequence: C | ||||||
Modified residue | 33 | 5-hydroxylysine | ||||
Sequence: K | ||||||
Glycosylation | 33 | O-linked (Gal...) hydroxylysine | ||||
Sequence: K | ||||||
Modified residue | 39 | 4-hydroxyproline | ||||
Sequence: P | ||||||
Modified residue | 45 | 4-hydroxyproline | ||||
Sequence: P | ||||||
Modified residue | 48 | 5-hydroxylysine | ||||
Sequence: K | ||||||
Glycosylation | 48 | O-linked (Gal...) hydroxylysine | ||||
Sequence: K | ||||||
Modified residue | 54 | 4-hydroxyproline | ||||
Sequence: P | ||||||
Modified residue | 57 | 4-hydroxyproline | ||||
Sequence: P | ||||||
Modified residue | 67 | 5-hydroxylysine | ||||
Sequence: K | ||||||
Glycosylation | 67 | O-linked (Gal...) hydroxylysine | ||||
Sequence: K | ||||||
Modified residue | 73 | 4-hydroxyproline | ||||
Sequence: P | ||||||
Modified residue | 79 | 4-hydroxyproline | ||||
Sequence: P | ||||||
Modified residue | 85 | 4-hydroxyproline | ||||
Sequence: P | ||||||
Modified residue | 100 | 5-hydroxylysine | ||||
Sequence: K | ||||||
Glycosylation | 100 | O-linked (Gal...) hydroxylysine | ||||
Sequence: K | ||||||
Glycosylation | 146 | N-linked (GlcNAc...) asparagine | ||||
Sequence: N |
Post-translational modification
O-linked glycans are assumed to be the Glc-Gal disaccharides typically found as secondary modifications of hydroxylated lysines in collagen-like domains.
Keywords
- PTM
Proteomic databases
PTM databases
Expression
Interaction
Subunit
C1 is a calcium-dependent trimolecular complex of C1q, R and S in the molar ration of 1:2:2. C1q subcomponent is composed of nine subunits, six of which are disulfide-linked dimers of the A and B chains, and three of which are disulfide-linked dimers of the C chain. Interacts (via C-terminus) with CD33; this interaction activates CD33 inhibitory motifs (PubMed:28325905).
Interacts with CR1 (via Sushi 24 and Sushi 25 domains) (PubMed:29563915, PubMed:9324355).
Antigen-bound IgM (via the Fc region) interacts with the globular domains of C1q component of the complement system, all three modules C1QA, C1QB and C1QC being involved in IgM binding; this interaction is multivalent. It initiates the classical complement pathway
Interacts with CR1 (via Sushi 24 and Sushi 25 domains) (PubMed:29563915, PubMed:9324355).
Antigen-bound IgM (via the Fc region) interacts with the globular domains of C1q component of the complement system, all three modules C1QA, C1QB and C1QC being involved in IgM binding; this interaction is multivalent. It initiates the classical complement pathway
(Microbial infection) Interacts with Staphylococcus aureus protein Cna; this interaction results in the inhibition of the classical complement pathway.
Binary interactions
Type | Entry 1 | Entry 2 | Number of experiments | Intact | |
---|---|---|---|---|---|
BINARY | P02745 | C1QB P02746 | 5 | EBI-1220209, EBI-2813376 | |
BINARY | P02745 | C1QBP PRO_0000018590 Q07021 | 6 | EBI-1220209, EBI-14032968 | |
BINARY | P02745 | SGTB Q96EQ0 | 3 | EBI-1220209, EBI-744081 | |
BINARY | P02745 | UBQLN2 Q9UHD9 | 6 | EBI-1220209, EBI-947187 |
Protein-protein interaction databases
Miscellaneous
Structure
Family & Domains
Features
Showing features for compositional bias, region, domain.
Type | ID | Position(s) | Description | |||
---|---|---|---|---|---|---|
Compositional bias | 27-48 | Basic and acidic residues | ||||
Sequence: RAPDGKKGEAGRPGRRGRPGLK | ||||||
Region | 27-114 | Disordered | ||||
Sequence: RAPDGKKGEAGRPGRRGRPGLKGEQGEPGAPGIRTGIQGLKGDQGEPGPSGNPGKVGYPGPSGPLGARGIPGIKGTKGSPGNIKDQPR | ||||||
Domain | 31-109 | Collagen-like | ||||
Sequence: GKKGEAGRPGRRGRPGLKGEQGEPGAPGIRTGIQGLKGDQGEPGPSGNPGKVGYPGPSGPLGARGIPGIKGTKGSPGNI | ||||||
Domain | 110-245 | C1q | ||||
Sequence: KDQPRPAFSAIRRNPPMGGNVVIFDTVITNQEEPYQNHSGRFVCTVPGYYYFTFQVLSQWEICLSIVSSSRGQVRRSLGFCDTTNKGLFQVVSGGMVLQLQQGDQVWVEKDPKKGHIYQGSEADSVFSGFLIFPSA |
Keywords
- Domain
Phylogenomic databases
Family and domain databases
Sequence
- Sequence statusComplete
- Sequence processingThe displayed sequence is further processed into a mature form.
- Length245
- Mass (Da)26,017
- Last updated1993-07-01 v2
- Checksum8FF6B6AE02D49C4C
Computationally mapped potential isoform sequences
There are 6 potential isoforms mapped to this entry
Entry | Entry name | Gene name | Length | ||
---|---|---|---|---|---|
X6RLJ0 | X6RLJ0_HUMAN | C1QA | 220 | ||
A0A8Q3SI41 | A0A8Q3SI41_HUMAN | C1QA | 77 | ||
A0A8Q3SI59 | A0A8Q3SI59_HUMAN | C1QA | 113 | ||
A0A8Q3SI63 | A0A8Q3SI63_HUMAN | C1QA | 120 | ||
A0A8Q3SI02 | A0A8Q3SI02_HUMAN | C1QA | 61 | ||
A0A8Q3SI08 | A0A8Q3SI08_HUMAN | C1QA | 62 |
Features
Showing features for compositional bias, sequence conflict.
Type | ID | Position(s) | Description | |||
---|---|---|---|---|---|---|
Compositional bias | 27-48 | Basic and acidic residues | ||||
Sequence: RAPDGKKGEAGRPGRRGRPGLK | ||||||
Sequence conflict | 97 | in Ref. 8; AA sequence | ||||
Sequence: P → K | ||||||
Sequence conflict | 103 | in Ref. 8; AA sequence | ||||
Sequence: K → P | ||||||
Sequence conflict | 172 | in Ref. 9; AA sequence | ||||
Sequence: C → N | ||||||
Sequence conflict | 178 | in Ref. 9; AA sequence | ||||
Sequence: S → W | ||||||
Sequence conflict | 240-243 | in Ref. 9; AA sequence | ||||
Sequence: LIFP → ILPGF |
Keywords
- Technical term
Sequence databases
Nucleotide Sequence | Protein Sequence | Molecule Type | Status | |
---|---|---|---|---|
AF135157 EMBL· GenBank· DDBJ | AAD32626.1 EMBL· GenBank· DDBJ | mRNA | ||
AY789471 EMBL· GenBank· DDBJ | AAV40828.1 EMBL· GenBank· DDBJ | Genomic DNA | ||
AL158086 EMBL· GenBank· DDBJ | CAI22892.1 EMBL· GenBank· DDBJ | Genomic DNA | ||
AK311980 EMBL· GenBank· DDBJ | BAG34919.1 EMBL· GenBank· DDBJ | mRNA | ||
AL158086 EMBL· GenBank· DDBJ | CAI22893.1 EMBL· GenBank· DDBJ | Genomic DNA | ||
CH471134 EMBL· GenBank· DDBJ | EAW95014.1 EMBL· GenBank· DDBJ | Genomic DNA | ||
BC030153 EMBL· GenBank· DDBJ | AAH30153.1 EMBL· GenBank· DDBJ | mRNA | ||
BC071986 EMBL· GenBank· DDBJ | AAH71986.1 EMBL· GenBank· DDBJ | mRNA |