Osh Proteins Control Nanoscale Lipid Organization Necessary for PI(4,5)P 2 Synthesis

The plasma membrane (PM) is composed of a complex lipid mixture that forms heterogeneous membrane environments. Yet how small-scale lipid organization controls physiological events at the PM remains largely unknown. Here, we show that ORP/Osh lipid exchange proteins are critical for the synthesis of phosphatidylinositol (4,5)-bisphosphate, PI(4,5)P2, a key regulator of dynamic events at the PM. In real-time assays, we find that unsaturated phosphatidylserine (PS) and sterols, both ORP/Osh protein ligands, synergistically stimulate phosphatidylinositol 4-phosphate 5-kinase (PIP5K) activity. Our biophysical and simulation analyses further reveal an unconventional co-segregation of unsaturated PS and phosphatidylinositol 4-phosphate (PI4P) species in sterol-containing membrane bilayers. Moreover, we show that Osh protein-mediated unsaturated PI4P/PS membrane lipid organization is sensed by the PIP5K specificity loop. Thus, ORP/Osh family members create an unsaturated phospholipid nanoscale environment that drives PIP5K activity and PI(4,5)P2 synthesis that ultimately controls global PM organization and dynamics.