background:
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. This gene localizes to 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. Two transcript variants encoding different isoforms have been found for this gene. [provided by RefSeq, Nov 2011].
Function:
C4 plays a central role in the activation of the classical pathway of the complement system. It is processed by activated C1 which removes from the alpha chain the C4a anaphylatoxin.
Subunit:
This protein is synthesized as a single-chain precursor and, prior to secretion, is enzymatically cleaved to form a trimer of non-identical chains (alpha, beta and gamma).
Subcellular Location:
Secreted.
DISEASE:
Defects in C4A are the cause of complement component 4A deficiency (C4AD). A rare defect of the complement classical pathway associated with the development of autoimmune disorders, mainly systemic lupus with or without associated glomerulonephritis.
Similarity:
Contains 1 anaphylatoxin-like domain.
Contains 1 NTR domain.
Database links:
Entrez Gene: 100293534 Human
Entrez Gene: 100507685 Human
Entrez Gene: 720 Human
Entrez Gene: 721 Human
Omim: 120810 Human
SwissProt: P0C0L4 Human
SwissProt: P0C0L5 Human
Unigene: 534847 Human
Unigene: 144022 Human
Important Note:
This product as supplied is intended for research use only, not for use in human, therapeutic or diagnostic applications.
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