Phosphatidylinositol phosphates (PIPs) and cholesterol are known to regulate the function of late endosomes and lysosomes (LELs). ORP1L, a putative lipid sensor/transporter, specifically localizes to LELs. Here, we show that the highly conserved lipid-binding domain of ORP1, ORP1-ORD, can transport sterols between membranes only in the presence of PI(4,5)P2 or PI(3,4)P2. Surprisingly however, ORP1-ORD can’t transport any PIPs in vitro. In cells, both ORP1L and PI(3,4)P2 were required for the efficient removal of cholesterol from LELs. The crystal structures of ORP1-ORD in complex with cholesterol or PI(4,5)P2 reveal that the N-terminal loop and the lid of ORP1-ORD play important roles in ORD oligomerization and function, and that the 5- or 3-phosphate group of PI(4,5)P2 or PI(3,4)P2 may facilitate ORP1-mediated cholesterol transport by keeping the lid of ORP1-ORD open. We further demonstrate that ORP1L can regulate mTORC1 signaling and autophagosome maturation by maintaining lysosomal lipid homeostasis. Thus, our work unveils a novel mechanism by which PIPs may regulate OSBP/ORPs-mediated transport of major lipid species such as cholesterol.
Hongyuan Yang, Email: h.rob.yang@unsw.edu.au