MPP1 interacts with DOPC/SM/Cholesterol in an artificial membrane system using Langmuir-Blodgett monolayer

The interaction between membrane palmitoylated protein -1 (MPP1) with lipid bi- and mono-layers composed of a DOPC/SM/Chol mixture was investigated. MPP1 co-migrates with liposomes to the top of the liposome flotation gradient, indicating binding of MPP1 with liposomes. The injection of MPP1 into the subphase of an LB monolayer of the above lipid composition induced an increase in surface pressure, indicating that MPP1 molecules were incorporated into the lipid monolayer. The compressibility modulus isotherms of MPP1, lipids and lipid-MPP1 films have essentially different shapes from one another. Pure MPP1 isotherms were characterized by a peak in surface pressure of 25-35 mNm-1. This transition disappears in isotherms obtained with lipid monolayers in the presence of MPP1, which suggests an interaction between the protein and the lipid monolayers. In addition, this interaction is sensitive to the presence of cholesterol in the lipid monolayer, as adding of MPP1 into the subphase of lipid monolayers containing cholesterol resulted in a much larger increase in surface area than when MPP1 is injected into the subphase of a lipid monolayer devoid of cholesterol. In conclusion, the data demonstrates that MPP1 interacts with lipid mixtures in two different model membrane systems.