The CRB3:PALS1:PATJ complex is the second major cell polarity protein complex at tight junctions (TJs) (Shin et al., 2006). The integral membrane protein CRB3 localizes to the apical domain of epithelial cells and is concentrated at TJs. CRB3 directly associates with PALS1(MPP5) which interacts with PATJ, a protein consisting of 10 PDZ domains. The interaction with CRB3 might recruit the MPP5:PATJ complex to TJs (Lemmers et al., 2002; Roh et al., 2003). Although its precise functions of the individual components have not been established, the complex is required for TJ formation, in part through the stabilization of apical and lateral components of tight junctions (Michel et al., 2005; Shin et al., 2005).
Severe acute respiratory syndrome coronavirus type 1 envelope protein (SARS-CoV-1 E) was found to interfere with host PDZ‐dependent interactions of MPP5 (PALS1) thus affecting TJ formation (Teoh KT et al. 2010).