Interaction of membrane palmitoylated protein-1 with model lipid membranes.

Membrane palmitoylated protein-1 (MPP1) plays an important role in the formation of raft domains in erythroid membranes. We have shown recently that MPP1 interacts with membrane lipids composed of dioleoylphosphatidylcholine (DOPC), sphingomyelin (SM) and cholesterol. Here we further extend this investigation. Our results obtained from FRET assays revealed that MPP1 binds liposomes with high affinity (KD ~ 135 ± 15 nM). Preincubation of MPP1 with cholesterol before its addition to the Langmuir subphase resultedin a dramatic reduction in the membrane insertion/binding of MPP1, indicating the role of direct MPP1/cholesterol complexes in the interaction of MPP1 with membrane lipids. The generalized polarization values of liposomes as well as the constant surface area experiments on monolayers composed of DOPC/SM/Chol indicated a change in the lipid mono- and bilayer properties upon the addition of MPP1. Furthermore, the presence of flotillins did not affect the binding of MPP1 to membrane lipids. Also, MPP1 containing palmitoylation-mimicking mutation (C242F) bound DOPC/SM/Chol mono- and bilayer with an affinity very similar to that obtained for wild-type MPP1. In conclusion, our results suggest that the direct binding of MPP1 with membrane lipids could be involved in the mechanism of membrane association of MPP1 in erythroid cells.