Recent studies have revealed another way that lipid metabolism occurs at MCSs; enzymes located in the ER can modify lipids in the plasma membrane at regions of close contact between these organelles.
In one report, the ER resident phosphatase Sac1 was found to dephosphorylate PIPs localized in the PM in yeast.
A second study suggested that Opi3, an enzyme in the ER that forms phosphatidylcholine (PC) from PE, can use PE in the
plasma membrane as a substrate.
Remarkably, lipidbinding proteins localized at ER–plasma membrane MCSs
regulate the activity of Sac1 and Opi3.
Thus lipid sensing at MCSs may regulate plasma membrane lipid composition.