Lipid transporter involved in lipid countertransport between the Golgi complex and membranes of the endoplasmic reticulum: specifically exchanges sterol with phosphatidylinositol 4-phosphate (PI4P), delivering sterol to the Golgi in exchange for PI4P, which is degraded by the SAC1/SACM1L phosphatase in the endoplasmic reticulum (By similarity). Binds cholesterol and a range of oxysterols including 25-hydroxycholesterol (PubMed:18165705). Cholesterol binding promotes the formation of a complex with PP2A and a tyrosine phosphatase which dephosphorylates ERK1/2, whereas 25-hydroxycholesterol causes its disassembly (By similarity). Regulates cholesterol efflux by decreasing ABCA1 stability (By similarity). Homodimer or homotrimer. Interacts (via FFAT motif) with VAPA. Interacts (via C-terminus) with RELCH (via the third HEAT repeat) (By similarity). Found in a complex composed of RELCH, OSBP1 and RAB11A (By similarity). Predominantly cytosolic. The PH and the Ala/Gly-rich domains control cholesterol binding without affecting 25-hydroxycholesterol binding. The second coiled-coil domain is required for interaction with the tyrosine phosphatase. The FFAT motif is required for interaction with VATA and proper localization of the protein. The N-terminus is blocked. Belongs to the OSBP family.