c4a c4a complement c4-a is a kind of the complement component 4 protein that in humans is encoded by the c4a gene. c4aavailable structurespdbortholog search: pdbe rcsb list of pdb id codes1hzf, 4fxg, 4fxk, 4xamidentifiersaliasesc4a, c4, c4a2, c4a3, c4a4, c4a6, c4ad, c4s, co4, cpamd2, rg, complement component 4a (rodgers blood group), complement c4a (rodgers blood group)external idsomim: 120810 mgi: 88228 homologene: 36030 genecards: c4a gene location (human)chr.chromosome 6 (human)band6p21.33start31,982,052 bpend32,002,681 bpgene location (mouse)chr.chromosome 17 (mouse)band17 b1|17 18.29 cmstart34,947,354 bpend34,962,856 bprna expression patternbgeehumanmouse (ortholog)top expressed inright lobe of liverright lobe of thyroid glandleft lobe of thyroid glandtibial nerveanterior pituitaryspleenkidneyleft uterine tubegallbladdersubstantia nigratop expressed inzone of skinadrenal glandwhite adipose tissuesynovial jointankle jointspleenliveruterusesophagusurinary bladdermore reference expression databiogpsmore reference expression datagene ontologymolecular 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 / quickgoorthologsspecieshumanmouseentrez72012268ensemblensg00000244207ensg00000206340ensg00000244731ensg00000227746ensmusg00000073418uniprotp0c0l4p01029refseq (mrna)nm_001252204nm_007293nm_009780refseq (protein)np_001239133np_009224np_033910location (ucsc)chr 6: 31.98 – 32 mbchr 17: 34.95 – 34.96 mbpubmed searchwikidataview/edit humanview/edit mouse 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. 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. this gene localizes to the rccx locus within the major histocompatibility complex (mhc) class iii region on chromosome 6. varying haplotypes of this gene cluster exist, such that individuals may have 1, 2, or 3 copies of this gene. each copy of the gene, due to five adjacent nucleotide substitutions cause four amino acid changes and immunological subfunctionalization, can be of one of two types: c4a and c4b. 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.