Involved in several stages of intracellular trafficking. Interacts with membranes containing phosphatidylinositol 3-phosphate (PtdIns(3P)) or phosphatidylinositol 3,5-bisphosphate (PtdIns(3,5)P2) (PubMed:12198132). Acts in part as component of the retromer membrane-deforming SNX-BAR subcomplex. The SNX-BAR retromer mediates retrograde transport of cargo proteins from endosomes to the trans-Golgi network (TGN) and is involved in endosome-to-plasma membrane transport for cargo protein recycling. The SNX-BAR subcomplex functions to deform the donor membrane into a tubular profile called endosome-to-TGN transport carrier (ETC) (Probable). Can sense membrane curvature and has in vitro vesicle-to-membrane remodeling activity (PubMed:19816406, PubMed:23085988). Involved in retrograde endosome-to-TGN transport of lysosomal enzyme receptors (IGF2R, M6PR and SORT1) and Shiginella dysenteria toxin stxB. Plays a role in targeting ligand-activated EGFR to the lysosomes for degradation after endocytosis from the cell surface and release from the Golgi (PubMed:12198132, PubMed:15498486, PubMed:17550970, PubMed:17101778, PubMed:18088323, PubMed:21040701). Involvement in retromer-independent endocytic trafficking of P2RY1 and lysosomal degradation of protease-activated receptor-1/F2R (PubMed:16407403, PubMed:20070609). Promotes KALRN- and RHOG-dependent but retromer-independent membrane remodeling such as lamellipodium formation; the function is dependent on GEF activity of KALRN (PubMed:20604901). Required for endocytosis of DRD5 upon agonist stimulation but not for basal receptor trafficking (PubMed:23152498). Predominantly forms heterodimers with BAR domain-containing sorting nexins SNX5, SNX6 and SNX32; can self-associate to form homodimers (PubMed:23085988). The heterodimers are proposed to self-assemble into helical arrays on the membrane to stabilize and expand local membrane curvature underlying endosomal tubule formation. Thought to be a component of the originally described retromer complex (also called SNX-BAR retromer) which is a pentamer containing the heterotrimeric retromer cargo-selective complex (CSC), also described as vacuolar protein sorting subcomplex (VPS) and a heterodimeric membrane-deforming subcomplex formed between SNX1 or SNX2 and SNX5 or SNX6 (also called SNX-BAR subcomplex); the respective CSC and SNX-BAR subcomplexes associate with low affinity (Probable). Interacts with SNX5, SNX6, SNX32, VPS26A, VPS29, VPS35, DRD5, DENND5A, KALRN, RHOG (GDP-bound form) (PubMed:9819414, PubMed:11102511, PubMed:19619496, PubMed:19935774, PubMed:19619496, PubMed:20604901, PubMed:23085988, PubMed:23152498). The interaction with SNX2 is reported controversially (PubMed:9819414, PubMed:11997453, PubMed:19619496, PubMed:23085988). Interacts with DNAJC13; prevented by presence of HGS (PubMed:19874558). Interacts with HGS (By similarity). Enriched on tubular elements of the early endosome membrane. Binds preferentially to highly curved membranes enriched in phosphatidylinositol 3-phosphate (PtdIns(3P)) or phosphatidylinositol 3,5-bisphosphate (PtdIns(3,5)P2) (PubMed:15498486). Colocalized with SORT1 to tubular endosomal membrane structures called endosome-to-TGN transport carriers (ETCs) which are budding from early endosome vacuoles just before maturing into late endosome vacuoles (PubMed:18088323). Colocalizes with DNAJC13 and Shiginella dysenteria toxin stxB on early endosomes (PubMed:19874558). Colocalized with F-actin at the leading edge of lamellipodia in a KALRN-dependent manner (PubMed:20604901). The BAR domain is able to sense membrane curvature upon dimerization (PubMed:19816406). Membrane remodeling seems to implicate insertion of a N-terminal amphipathic helix (AH) in the membrane (Probable). Binds phosphatidylinositol 3-phosphate (PtdIns-(3)P) and phosphatidylinositol 3,5-bisphosphate (PtdIns-(3,5)P2) in liposome-based assays. Can bind PtdIns(3,4,5)P3 in protein:lipid overlay assays, but not in liposome-based assays. Belongs to the sorting nexin family.