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. Author manuscript; available in PMC: 2018 Nov 1.
Published in final edited form as: Trends Cell Biol. 2017 Aug 30;27(11):833–850. doi: 10.1016/j.tcb.2017.07.006

Fig. 2. Lipid transfer proteins mediate lipid exchange between membranes.

Fig. 2

Sterols and phospholipids are transferred between two adjacent organelle membranes via lipid transfer proteins. ER anchored VAP serves as the interacting partner for various lipid transfer proteins including OSBP on the Golgi as well as ORP1L and STARD3 on the LE/LY. ORP1L and STARD3 are involved in cholesterol transfer from the LE/LY to the ER and from the ER to the LE/LY, respectively. ORP5 is a VAP-independent ER associated protein that interacts with NPC1 and is thought to act as a cholesterol acceptor, thus facilitating lysosomal cholesterol export. At the Golgi, OSBP transports PI4P down its concentration gradient to the ER, where the PI4P specific phosphatase Sac1 hydrolyzes it to PI to maintain low levels of PI4P at the ER membrane. After depositing the PI4P at the ER, OSBP binds cholesterol and transfers it to the Golgi, thus completing the cycle and establishing a net transfer of cholesterol in the ER-to-Golgi direction.