FIGURE 1: Predicted topological model of P4-ATPase and its regulatory subunit Cdc50.

Cdc50 interacts with P4-ATPase through its exocytoplasmic loop to activate the lipid flippase function, which translocates specific phospholipids from the exocytoplasmic leaflet to the cytoplasmic leaflet of the lipid bilayer membrane. SM: sphingomyelin, PC: phosphatidylcholine, PS: phosphatidylserine, PE: phosphatidylenthanolamine, PI: phosphatidylinositol.