C4A
Available structures PDB Ortholog search: PDBe RCSB List of PDB id codes 1HZF, 4FXG, 4FXK, 4XAM
Identifiers
Aliases	C4A, C4, C4A2, C4A3, C4A4, C4A6, C4AD, C4S, CO4, CPAMD2, RG, complement component 4A (Rodgers blood group), complement C4A (Rodgers blood group)
External IDs	OMIM: 120810 MGI: 88228 HomoloGene: 36030 GeneCards: C4A
Gene location (Human) Chr. Chromosome 6 (human)[1] Band 6p21.33 Start 31,982,052 bp[1] End 32,002,681 bp[1]
Gene location (Mouse) Chr. Chromosome 17 (mouse)[2] Band 17 B1|17 18.29 cM Start 34,947,354 bp[2] End 34,962,856 bp[2]
RNA expression pattern Bgee Human Mouse (ortholog) Top expressed in right lobe of liver right lobe of thyroid gland left lobe of thyroid gland tibial nerve anterior pituitary spleen kidney left uterine tube gallbladder substantia nigra Top expressed in zone of skin adrenal gland white adipose tissue synovial joint ankle joint spleen liver uterus esophagus urinary bladder More reference expression data BioGPS More reference expression data
Gene ontology Molecular function endopeptidase inhibitor activity complement component C1q complex binding serine-type endopeptidase activity Cellular component extracellular region plasma membrane extracellular exosome blood microparticle cell projection dendrite cell junction synapse axon neuronal cell body extracellular space endoplasmic reticulum lumen Biological process complement activation inflammatory response positive regulation of apoptotic cell clearance regulation of complement activation negative regulation of endopeptidase activity complement activation, classical pathway immune system process innate immune response proteolysis post-translational protein modification Sources:Amigo / QuickGO
Orthologs Species Human Mouse Entrez 720 12268 Ensembl ENSG00000244207 ENSG00000206340 ENSG00000244731 ENSG00000227746 ENSMUSG00000073418 UniProt P0C0L4 P01029 RefSeq (mRNA) NM_001252204 NM_007293 NM_009780 RefSeq (protein) NP_001239133 NP_009224 NP_033910 Location (UCSC) Chr 6: 31.98 – 32 Mb Chr 17: 34.95 – 34.96 Mb PubMed search [3] [4]
Wikidata
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Complement C4-A is a kind of the Complement component 4 protein that in humans is encoded by the C4A gene.^[5]

Function

This gene encodes the acidic form of complement factor 4, part of the classical activation pathway. The protein is expressed as a single chain precursor which is proteolytically cleaved into a trimer of alpha, beta, and gamma chains prior to secretion. The trimer provides a surface for interaction between the antigen-antibody complex and other complement components. The alpha chain may be cleaved to release C4 anaphylatoxin, a mediator of local inflammation. Deficiency of this protein is associated with systemic lupus erythematosus and type I diabetes mellitus.^{[6][7][8][9][10][11]} Excess production due to a copy number that is higher than normal has shown a high probability of a causal relationship with schizophrenia and bipolar disorder with psychosis, which could explain the hereditary nature of these illnesses.^[12] This gene localizes to the RCCX locus within the major histocompatibility complex (MHC) class III region on chromosome 6.^[13][14] Varying haplotypes of this gene cluster exist, such that individuals may have 1, 2, or 3 copies of this gene.^[5] Each copy of the gene, due to five adjacent nucleotide substitutions cause four amino acid changes and immunological subfunctionalization,^[15] can be of one of two types: C4A and C4B.^[16] Each gene contains 41 exons and has a dichotomous size variation between approximately 22 kb and 16 kb, with the longer variant being the result of the integration of the endogenous retrovirus HERV-K(C4) into intron 9.^[14]