J chain

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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.
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.[1] It is a 137 residue polypeptide.[2]

Structure[edit]

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.[3]

The J-chain shows a large degree of homology between avian and human species, suggesting that it serves an important function.[3]

Function[edit]

The J Chain is required for IgM or IgA to be secreted into mucosa.[2]

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 case, there are also fewer IgA dimers.[2]

References[edit]

  1. ^ Levinson. Medical Microbiology and Immunology (11 ed.). McGrawHill. pp. 405–6. 
  2. ^ a b c Schroeder, Harry; Wald, David; Greenspan, Neil (2008). "Chapter 4: Immunoglobulins: Structure and Function". In Paul, William. Fundamental Immunology (Book) (6th ed.). Philadelphia, PA: Lippincott Williams & Wilkins. pp. 125–151. ISBN 0-7817-6519-6. 
  3. ^ a b Kiyono, Hiroshi; Kunisawa, Jaw; McGhee, Jerry; Mestecky, Jiri (2008). "Chapter 31: The Mucosal Immune System". In Paul, William. Fundamental Immunology (Book) (6th ed.). Philadelphia, PA: Lippincott Williams & Wilkins. pp. 983–1030. ISBN 0-7817-6519-6.