Occludin is a protein that in humans is encoded by the OCLN gene.[3][4] Occludin is a 65-kDa (522-amino acid polypeptide -human) integral plasma-membrane protein located at the tight junctions, described for the first time in 1993 by Shoichiro Tsukita.[5] Together with the Claudin group of proteins, it is the main component of the tight junctions.