title: OSBP-Related Protein Family in Lipid Transport Over Membrane Contact Sites.
abstract: Increasing evidence suggests that oxysterol-binding protein-related proteins (ORPs) localize at membrane contact sites, which are high-capacity platforms for inter-organelle exchange of small molecules and information. ORPs can simultaneously associate with the two apposed membranes and transfer lipids across the interbilayer gap. Oxysterol-binding protein moves cholesterol from the endoplasmic reticulum to trans-Golgi, driven by the retrograde transport of phosphatidylinositol-4-phosphate (PI4P). Analogously, yeast Osh6p mediates the transport of phosphatidylserine from the endoplasmic reticulum to the plasma membrane in exchange for PI4P, and ORP5 and -8 are suggested to execute similar functions in mammalian cells. ORPs may share the capacity to bind PI4P within their ligand-binding domain, prompting the hypothesis that bidirectional transport of a phosphoinositide and another lipid may be a common theme among the protein family. This model, however, needs more experimental support and does not exclude a function of ORPs in lipid signaling.
authors.affiliation: Minerva Foundation Institute for Medical Research, Biomedicum 2U, Helsinki, Finland. ; Department of Anatomy, Faculty of Medicine, University of Helsinki, Finland.
authors.forename: Vesa M
authors.initials: VM
authors.lastname: Olkkonen
keywords: OSBP-related protein; OSBPL gene; lipid signaling; lipid transport; membrane contact site; oxysterol-binding protein (OSBP)