Measurement of ORP10-Mediated Lipid Countertransport at ER-Endosome Membrane Contact Sites via a Chemically Induced
Asami Kawasaki1, Fubito Nakatsu2
1Department of Neurochemistry and Molecular Cell Biology, Niigata University School of Medicine and Graduate School of Medical/Dental Sciences, Niigata, Japan.
Abstract:
Oxysterol-binding protein (OSBP)-related proteins (ORPs) are a large family of lipid transfer proteins (LTPs) in mammals. ORPs mediate the countertransport of two distinct lipids at membrane contact sites (MCSs). ORP10 is localized via binding to ORP9 at the endoplasmic reticulum (ER)-endosome MCSs, where it mediates countertransport of phosphatidylinositol 4-phosphate (PI4P) and phosphatidylserine (PS). To quantitatively monitor the lipid countertransport process mediated by ORP10 in situ, we take advantage of chemically induced dimerization (CID), a strategy of inducing protein-protein interactions by exposure to chemicals. Specifically, we exploit the rapamycin-inducible heterodimerization of FKBP/FRB to acutely recruit the lipid transfer domain of ORP10 to the ER-endosome MCSs and monitor the levels of PI4P and PS on endosomes by their genetic probes in live imaging. This approach enables the measurement of ORP10 activity in lipid countertransport at ER-endosome MCSs and is also beneficial as a versatile method applicable to other LTPs.
