The Bin/Amphiphysin/Rvs (BAR) domain of Sorting Nexin 6
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. SNX6 forms a stable complex with SNX1 and may be a component of the retromer complex, a membrane coat multimeric complex required for endosomal retrieval of lysosomal hydrolase receptors to the Golgi, acting as a mammalian equivalent of yeast Vsp17p. It interacts with the receptor serine/threonine kinases from the transforming growth factor-beta family. It also plays roles in enhancing the degradation of EGFR and in regulating the activity of Na,K-ATPase through its interaction with Translationally Controlled Tumor Protein (TCTP). BAR domains form dimers that bind to membranes, induce membrane bending and curvature, and may also be involved in protein-protein interactions.