DSC study of the interaction of the prion peptide PrP106-126 with artificial membranes

The incorporation of the human prion peptide PrP106-126 into 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) and 1,2-dipalmitoyl-sn-glycero-3-phosphoethanolamine (DPPE) host model membranes has been investigated by differential scanning calorimetry. Two different types of peptide-membrane interactions have been studied. In one case, the peptide is obliged to be included into the hydrocarbon region of the lipid bilayer, in the other case, it is allowed to interact with the external surface of the membrane. The PrP106-126 incorporated into the DPPC membrane shows an increase in the gel-liquid crystal transition temperature of the bilayer with a decreased enthalpy change. The "oriented'' insertion of the hydrophobic part of the fragment into the bilayer, with a consequent increase in the order of the lipidic hydrocarbon chains in the gel state, is responsible for this behavior. Independently from the procedure adopted for the preparation of the sample, the PrP106-126 fragment interacts strongly and irreversibly with the host membrane. In contrast, when PrP106-126 is incorporated in the DPPE model membrane, the gel-liquid crystal transition temperature of the bilayer and the associated enthalpy change decrease. When added externally to the DPPE model membrane, the PrP106-126 fragment has no effect on the phase behavior of the bilayer. These findings suggest that PrP106-126 has a specific affinity for DPPC membranes that might correspond to the external surface of cells.