Occludin (OCLN)

Occludin is a 65-kDa (504-amino acid polypeptide) integral plasma-membrane protein located specifically at tight junctions described for the first time in 1993 by S Tsukita.According to its overall hydrophilicity, occludin appears to span the plasma membrane four times, forming two extracellular loops and exposing its NH2 and COOH terminus to the cytosol.

Interaction of occludin with several cytoplasmic proteins of the junctional plaque has been found to occur via its COOH terminus, while the extracellular loops are thought to be involved in the regulation of paracellular permeability and cell adhesion. Phosphorylation/dephosphorylation plays a major role in regulation of occludin and tight junctions.