J chain

Joining chain of multimeric IgA and IgM
Identifiers
Symbols	JCHAIN ; IGCJ; IGJ; JCH
External IDs	OMIM: 147790 MGI: 96493 HomoloGene: 16958 GeneCards: JCHAIN Gene
Gene ontology Molecular function • single-stranded DNA binding • antigen binding • IgA binding • phosphatidylcholine binding • immunoglobulin receptor binding • protein homodimerization activity • peptidoglycan binding Cellular component • extracellular region • extracellular space • extracellular exosome • monomeric IgA immunoglobulin complex • dimeric IgA immunoglobulin complex • secretory IgA immunoglobulin complex • secretory dimeric IgA immunoglobulin complex • pentameric IgM immunoglobulin complex • hexameric IgM immunoglobulin complex • blood microparticle Biological process • retina homeostasis • adaptive immune response • glomerular filtration • immune response • antibacterial humoral response • positive regulation of protein oligomerization • innate immune response • positive regulation of respiratory burst Sources: Amigo / QuickGO
RNA expression pattern
File:PBB GE IGJ 212592 at tn.png
More reference expression data
Orthologs
Species	Human	Mouse
Entrez	3512	16069
Ensembl	ENSG00000132465	ENSMUSG00000067149
UniProt	P01591	P01592
RefSeq (mRNA)	NM_144646	NM_152839
RefSeq (protein)	NP_653247	NP_690052
Location (UCSC)	Chr 4: 70.66 – 70.68 Mb	Chr 5: 88.52 – 88.53 Mb
PubMed search	[1]	[2]

Immunoglobulin M (IgM) pentameric antibody molecule (consisting of five base units).
1: Base unit.
2: Heavy chains.
3: Light chains.
4: J chain.
5: Intermolecular disulfide bonds.

File:Immunglobulin A as Dimer.png

The dimeric IgA molecule.
1: Heavy chains.
2: Light chains.
3: J-chain.
4: Secretory component.

A J chain is a protein component of the antibodies IgM and IgA. It is a 137 residue polypeptide, encoded by the IGJ gene.

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.