The Bin/Amphiphysin/Rvs (BAR) domain of Sorting Nexins 5 and 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. Members of this subfamily include SNX5, SNX6, the mammalian SNX32, and similar proteins. SNX5 and SNX6 may be components 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. The function of SNX32 is still unknown. BAR domains form dimers that bind to membranes, induce membrane bending and curvature, and may also be involved in protein-protein interactions.