Occludin is an integral membrane protein located at the tight junction. It is a tetraspanin protein with four transmembrane domains,intracellular N and C termini and two extracellular loops. Occludin plays a role in the formation and regulation of the tight junction paracellular permeability barrier. Occludin can exist in different isoforms,owing to modifications at the posttranscriptional and posttranslational levels .