The Bin/Amphiphysin/Rvs (BAR) domain of Sorting Nexin 4
BAR domains are dimerization, lipid binding and curvature sensing modules found in many different proteins with diverse functions. Sorting nexins (SNXs) are Phox homology (PX) domain containing proteins that are involved in regulating membrane traffic and protein sorting in the endosomal system. SNXs differ from each other in their lipid-binding specificity, subcellular localization and specific function in the endocytic pathway. A subset of SNXs also contain BAR domains. The PX-BAR structural unit determines the specific membrane targeting of SNXs. SNX4 is involved in recycling traffic from the sorting endosome (post-Golgi endosome) back to the late Golgi. It is also implicated in the regulation of plasma membrane receptor trafficking and interacts with receptors for EGF, insulin, platelet-derived growth factor and leptin. BAR domains form dimers that bind to membranes, induce membrane bending and curvature, and may also be involved in protein-protein interactions.