Occludin is a transmembrane adhesion protein which can be found embedded within tight junctions at exact positions to form the correct network. Along with claudin it acts as one of the main proteins forming the sealing strands within the junction which are important for communication across the intracellular space between the strands. However, the exact function of occludin is still unknown.
There is strong evidence that the presence of occludin is directly linked to the permeability of epithelial cells, such evidence includes the fact that the level of occuldin in the tight junctions of the cell-cell contacts in the neural endothelium is high and the distribution is continuous compared to the reduced and non-continuous levels of occludin in the cell to cell contacts of non neural endothelial cells. This is significant due to the relatively more permeable endothelial cells in the brain.