C4A

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 is cleaved to release C4 anaphylatoxin, an antimicrobial peptide and 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 2014]

本基因编码补体因子4的酸性形式，其为经典激活途径的组成部分。该蛋白质以单链前体的形式表达，在分泌前通过蛋白酶解裂为α、β和γ链的三聚体。该三聚体为抗原-抗体复合物与其他补体成分之间的相互作用提供了界面。α链被裂解以释放C4过敏性毒素、一种抗菌肽和局部炎症的介质。该蛋白质的缺乏与系统性红斑狼疮和I型糖尿病相关。该基因定位于第6号染色体上的主要组织相容性复合体（MHC）III区。存在该基因簇的变异等位基因，因此个体可能拥有1、2或3个该基因拷贝。对于该基因已发现两种转录变体，它们编码不同的异构体。[由RefSeq提供，2014年11月]