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Updated: May 26, 2026

Fluorescence-Based Measurements of Phosphatidylserine/Phosphatidylinositol 4-Phosphate Exchange Between Membranes
Published on: March 14, 2021
Osh4p exchanges sterols for phosphatidylinositol 4-phosphate between lipid bilayers
Maud de Saint-Jean1, Vanessa Delfosse, Dominique Douguet
1Institut de Pharmacologie Moléculaire et Cellulaire, Université de Nice Sophia-Antipolis and Centre National de la Recherche Scientifique, 06560 Valbonne, France.
Osh4p/Kes1p protein transports sterols and phosphatidylinositol 4-phosphate (PI(4)P) between cellular compartments. This lipid exchange mechanism helps create sterol gradients, linking sterol transport and PI(4)P metabolism.
Area of Science:
- Cell Biology
- Biochemistry
- Molecular Biology
Background:
- Osh/Orp proteins are key players in intracellular sterol transport and phosphoinositide metabolism.
- The functional relationship between sterol transport and phosphoinositide metabolism by Osh/Orp proteins is not well understood.
Purpose of the Study:
- To investigate the influence of membrane composition on Osh4p/Kes1p's ability to transport sterols, specifically dehydroergosterol (DHE).
- To elucidate the mechanism by which Osh4p interacts with and transports phosphatidylinositol 4-phosphate (PI(4)P).
Main Methods:
- Development of novel assays to study lipid extraction and transport.
- Structural determination of the Osh4p-PI(4)P complex.
- In vitro lipid exchange assays.
Main Results:
- Phosphatidylinositol 4-phosphate (PI(4)P) was found to inhibit dehydroergosterol (DHE) extraction by Osh4p.
- Osh4p efficiently extracts PI(4)P and can substitute it for sterols.
- Structural analysis revealed the mechanism of selective PI(4)P binding and substitution.
- Osh4p facilitates bidirectional transport of DHE and PI(4)P between membranes.
Conclusions:
- Osh4p functions as a sterol/PI(4)P exchanger, transporting sterols from the ER to PI(4)P-rich compartments and PI(4)P back.
- This transport cycle, coupled with PI(4)P metabolism, may establish cellular sterol gradients.
- Conserved residues suggest other Osh/Orp proteins may also function as sterol/phosphoinositide exchangers.
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