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| Identifiers | |||||||||||||||||||||||||||||||||||||||||||||||||||
| Aliases | C4B, C4B1, C4B12, C4B2, C4B3, C4B5, C4BD, C4B_2, C4F, CH, CO4, CPAMD3, Complement component 4B, complement component 4B (Chido blood group), complement C4B (Chido blood group) | ||||||||||||||||||||||||||||||||||||||||||||||||||
| External IDs | OMIM:120820;MGI:88228;HomoloGene:36030;GeneCards:C4B;OMA:C4B - orthologs | ||||||||||||||||||||||||||||||||||||||||||||||||||
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| Wikidata | |||||||||||||||||||||||||||||||||||||||||||||||||||
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Complement component 4B (Chido blood group) is a kind of theComplement component 4protein that in humans is encoded by the C4Bgene.[5]
This gene encodes the basic form of complement factor 4, part of the classical activation pathway. The protein is expressed as a single chain precursor which isproteolytically cleaved into a trimer of alpha, beta, and gamma chains prior to secretion. The trimer provides a surface forinteraction between the antigen-antibody complex and other complement components. The alpha chain may be cleaved to release C4anaphylatoxin, a mediator of local inflammation. Deficiency of this protein is associated with systemiclupus erythematosus. This gene localizes to theRCCX locus within the majorhistocompatibility complex (MHC) class III region on chromosome 6.[6][7] Varyinghaplotypes of this gene cluster exist, such that individuals may have 1, 2, or 3 copies of this gene. In addition, this gene exists as a long form and a short form due to the presence or absence of a 6.4 kb endogenousHERV-K retrovirus inintron 9. [provided by RefSeq, Jul 2008].[5] Each copy of the gene, due to five adjacent nucleotide substitutions cause four amino acid changes and immunological subfunctionalization,[8] can be of one of two types:C4A andC4B.[9] Each gene contains 41exons 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.[7]
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