Freitag vormittags Vorträge - Bunsentagung - Technische Universität ...

Freitag 21.05.2004, 17:10 Uhr
Vortrag - Hauptthema
Coupling of DNA to zwitterionic Phospholipid
Monolayers
Sandra Gromelski, , Gerald Brezesinski
Max Planck Institute of Colloids and Interfaces, D-14476
Golm/Potsdam, Germany
A
9
The use of viruses as a gene delivery system has a decisive
disadvantage: antigens on the top of the virus particle cause
immune reactions that can lead to destruction of the virus.
Therefore, artificial viruses are considered to be very promising
drug delivery systems. In order to investigate possibilities
to create artificial viruses using self-assembled polyelectrolyte
capsules covered by a lipid bilayer, the coupling of charged
lipids to (oppositely) charged polyelectrolytes is studied. In a
second step, DNA can be attached to the lipid surface. Therefore,
the understanding of this coupling process is important.
Monolayers (two-dimensional systems) on fluid subphases are
simple membrane models. Monolayer experiments have the advantage
that the molecular density of the layer can be varied
in an easy and well-defined way. Grazing incidence X-ray diffraction
was used in combination with Langmuir film balance
measurements to study the coupling of DNA with phospholipid
monolayers. The adsorption of calf thymus DNA (0.1 mM) on a
DMPE (1,2-dimyristoyl-phosphatidylethanolamine) monolayer
with and without the presence of CaCl2 and MgCl2 (1 mM)
was studied. The monolayer structure on the saline subphase
is slightly changed in comparison with the DMPE structure on
water. At low surface pressure, an oblique structure is observed.
The hydrophobic chains are tilted in a non-symmetry direction.
Increasing pressure leads to a transition to a NN (nearest
neighbor) tilted rectangular structure and then to a hexagonal
packing of upright oriented molecules. Apparently, DNA does
not couple to the zwitterionic DMPE monolayer in the absence
of divalent ions. There is no change in the pressure/area isotherm
nor in the lipid structure as compared with that on the
pure subphase. Changes in the isotherm show that the presence
of divalent cations leads to an interaction between DNA and
DMPE. An additional Bragg peak is observed at small Qxy values
indicating an ordered adsorption of DNA. The influence of
lipid packing density on the observed order of adsorbed DNA
will be discussed together with an adsorption model.