The Bin/Amphiphysin/Rvs (BAR) domain of Sorting Nexin 1
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. SNX1 is a component of the retromer complex, a membrane coat multimeric complex required for endosomal retrieval of lysosomal hydrolase receptors to the Golgi. The retromer consists of a cargo-recognition subcomplex and a subcomplex formed by a dimer of sorting nexins (SNX1 and/or SNX2), which ensures effcient cargo sorting by facilitating proper membrane localization of the cargo-recognition subcomplex. SNX1 is localized to a microdomain in early endosomes where it regulates cation-independent mannose-6-phosphate receptor retrieval to the trans Golgi network. BAR domains form dimers that bind to membranes, induce membrane bending and curvature, and may also be involved in protein-protein interactions.