Lipid transport protein (LTP) involved in non-vesicular transfer of lipids between membranes. Functions in phosphoinositide-coupled directional transport of various lipids by carrying the lipid molecule in a hydrophobic pocket and transfering it between membranes through the cytosol. Involved in maintenance of intracellular sterol distribution and homeostasis (PubMed:20008566, PubMed:15173322, PubMed:16136145, PubMed:22162133). 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 delivered to the ER-localized PI4P phosphatase SAC1 for degradation. Thus, by maintaining a PI4P gradient at the ER/Golgi interface, SAC1 may drive PS transport (PubMed:25849868, PubMed:16136145, PubMed:22162133). Displays a similar affinity for PI4P and sterols (PubMed:22162133). Binds sterol and PI4P in a mutually exclusive manner (PubMed:22162133). Involved in ergosterol transport from the plasma membrane (PM) to the ER (PubMed:16585271). Mediates sterol transport from the ER to mitochondria (PubMed:29487131). Involved in the negative regulation of Golgi-derived transport vesicle biogenesis (PubMed:8978672). Plays a role in the positive regulation of vesicular transport of ceramide from the ER to the Golgi, negatively regulating COPII-mediated ER export of cargos (PubMed:24213531). The OSBP-related domain (ORD) mediates binding of sterols and phospholipids. It displays an incomplete beta-barrel containing a central hydrophobic tunnel that can accommodate a single lipid molecule with a flexible lid covering the tunnel entrance. The ORD can bind two membranes simultaneously. It has at least two membrane-binding surfaces; one near the mouth of the lipid-binding pocket and a distal site that can bind a second membrane. These structural features correlate with the phosphatidylinositol 4-phosphate (PI(4)P)-coupled lipid transport optimized in closely apposed membranes, such as organelle contact sites. The lipid transfer cycle starts from the association of the LTP with a donor membrane, which accompanies conformational changes that uncover the ligand-binding pocket. The tunnel opening is generally mediated by displacement of the lid covering the binding pocket allowing uptake or release of a lipid molecule. The LTPs extract the lipid from the membrane by providing a hydrophobic environment as well as specific interaction. Dissociation from the donor membrane shifts the conformation to a closed form. Then, the LTPs loaded with a cargo lipid diffuse through the aqueous phase. Lid opening may be induced by the interaction of a hydrophobic side of the lid with the target membranes. The ArfGAP1 lipid packing sensor (ALPS) motif is a membrane-binding motif that is sensitive to curvature. Present with 32200 molecules/cell in log phase SD medium. Belongs to the OSBP family.