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
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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 problem