Species Human Entrez 3512 | Human Mouse Ensembl ENSG00000132465 | |
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Aliases JCHAIN, IGCJ, JCH, IGJ, J chain, joining chain of multimeric IgA and IgM External IDs MGI: 96493 HomoloGene: 16958 GeneCards: JCHAIN | ||
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A J chain is a protein component of the antibodies IgM and IgA. It is a 137 residue polypeptide, encoded by the IGJ gene.
Contents
J chain
Structure
The J Chain's molecular weight is approximately 15 kDa. It exhibits a standard immunoglobulin folding structure of two β-pleated sheets of four ribbons folded against one another. It has 8 cystine residues. Two of these residues link the α chains of IgA or the μ chains of IgM via disulfide bridges, effectively serving as the "glue" between two Fc regions of the antibody.
The J-chain shows a large degree of homology between avian and human species, suggesting that it serves an important function.
Function
The J Chain is required for IgM or IgA to be secreted into mucosa.
Because IgM and IgA are the only two types of antibody that polymerize, initial hypotheses stated that J chain was required for polymerization. However, it was subsequently found that IgM is able to polymerize in the absence of J chain as both a pentamer and a hexamer, however, both of these exist to lesser numbers in organisms lacking J chains. In such cases, there are also fewer IgA dimers.