A family of sterol sensors/transporters at membrane contact sites: Regulation of ORP-VAP complexes by sterol ligands

The functions of lipids as signaling compounds and their interorganelle transport are topics that have recently moved to the center stage of cell biological and biomedical research. In this context the concept of membrane contact sites (MCS), sites of close apposition of organelle membranes, is an emerging major theme. An increasing number of studies have revealed crucial roles of such contacts as sites with prominent functions in interorganelle lipid transport and metabolism as well as signaling nodes, and molecular machineries operating at MCSs are being identified (reviewed by ). One of the protein families reported to localize at membrane contacts are the Oxysterol-binding protein/OSBP-related proteins (ORPs), sterol/phospholipid binding proteins implicated in a variety of cellular functions: lipid metabolism and transport, vesicle transport and signaling cascades .