Poly-(amino acid) polyelectrolyte films: Structure and interactions with proteins and lipids

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Summary Following layer-by-layer build-up of poly-(L-glutamic acid)/poly-(L-lysine) (PGA/PLL) multilayers, we could demonstrate the gradual formation of a strong b secondary structure in the polyelectrolyte films. When the chemically very similar poly-(Laspartic acid) (PAA) was used as polyanion, the secondary structure of the polypeptide film was markedly different, it contained sizable amount of a-helix, and random structure as well. PGA and PAA could substitute each other in the polyelectrolyte films, but the structural consequences of the substitutions were not symmetrical: While PAA could be incorporated without large effects, the incorporation of PGA into an existing PAA/PLL film caused major structural rearrangement. The different effects can be related to the longer side chain in the glutamic acid, which results loosened polyelectrolyte film structure. We could create a lipid bilayer on the surface of PGA/PLL polyelectrolyte films. In addition, these lipid bilayers could be 10 covered with another polyelectrolyte layers, thus the lipid double layer was embedded into the polyelectrolyte architecture. This system may provide a tool to incorporate lipid-soluble, hydrophobic compounds into the highly charged polyelectrolyte films, which would be important for practical applications. Moreover, such a lipid double layer may be considered as a new model membrane system, where protein-lipid and protein-membrane interactions can be studied. The underlying polypeptide polyelectrolytes provide a large-scale protein-like surface, thus they can mimic the cytoskeleton, the protein network, which stabilizes the cell membrane. Finally, we made a first attempt to check, whether such artificial lipid bilayers can affect the activity of bio-functionalized polypeptide surfaces. PGA/PLL films, functionalized by a covalently bound melanocyte-stimulating hormone (a-MSH) were covered with lipid double layers. The melanoma cells coming in contact with these surfaces produced somewhat more melanin when the polyelectrolyte architecture contained the lipid double layer as well. These preliminary experiments show, that upon optimization of the lipid composition, and the polyelectrolyte architecture for each intended application, such systems might have practical use in solving biomedical problems

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