STRUCTURE AND PHASEBEHAVIOR OF CATIONIC-LIPID
DNA COMPLEXES
Joachim Rädler, MPI for Polymer Research, Mainz, GERMANY
1. Introduction
Schematic Drawing of the DNA double helix and a cationic lipid membrane
1
a)
b)
Int [arb. units]
6
10
5
10
0.2
0.4
-1
0.6
q [Å]
c)
d)
(a) Mixing and condensation of cationic liposomes and DNA. Vesicles fuse and form
multilamellar aggregates with DNA (b) In dilute suspension the particles are only fraction of
micron large. Electron microscopy image of one such "Lipoplex". Striation in the complexes
can be seen. (c) Structure of the lamellar lipid-DNA complexes as derived from small-angle Xray scattering (SAXS) (d) SAXS data of DOPC/DOTAP-DNA-mixtures showing six equidistant
reflections and one additional broad reflection.
2
2. Mesomorphic Polymorphism
Left: X-ray scattering data exhibit Debye-Scherrer ring pattern of a lipid-DNA powder
sample. right: photograph of a sample in a glas capillary. bottom : Setup of the
beamline X13 at DESY for simultaneous recording of sall and wide angle scattering
[Rappolt 1996].
3
a)
b)
.
(a) Schematic drawing of the
lamellar-columnar structure
(b) Electron density map of a
DMPC/DMTAP-DNA mixture,
obtained from the scattering
data shown in (c).
c)
4
lamellar nematic
L  N
lamellar “sliding”
L  SC
lamellar columnar
L  Drd
inv. hexagonal
HII  Dhd
hexagonal micellar
HI  Dhd
micellar
M I
isotropic
L3  I
Nomenclature for Lipid-Polymer composite phases
For lyotropic lipid phases a nomenclature is used, which was introduced by Luzatti,
one of the early pioneers in small angle X-ray structure characterization [Tardieu 1971]. For
lipid-DNA complexes this nomenclature is sometimes extended by an index „c“ for
condensed or complexed.
Here we like to suggest a mixed nomenclature that assigns lipid and polymer phase
separately. For example the lamellar-columnar phase may be descibed by the double
symbole L  Drd , where L denotes a fluid lamellar lipid phase and Drd denotes an
orthogonal-columnaren rod-lattice of DNA strands. The later symbole is derived from the
common liquid crystal notation, where “D” stand for discotic-columnar, „r“ for rectangular
and „d“ for disordered (i.e. no correlatons along the columnar axes). The symbol „  “ may
be taken as intercalation or superposition.
5
3. Phase transitions in lipid-DNA complexes
3.1 Lyotropic phase behavior : the dilution line
d DNA 
AD  D
 m L
80
L D (dilution equation)
80
dmem
60
dDNA
50
40
30
+
dmem, dDNA [Å]
dmem, dDNA [Å]
70
dmem
70
60
dDNA
50
40
30
L /D=1
20
+
o
L /L = 1
20
0
1
2
3
4
5
0
 = L+ /(L++L0)
1
2
= L+/D
3
4
DOPC/DOTAP--DNA-complexes : The DNA-DNA separation distance is plotted as a function
of the molar charge density  (left) and as a function of the lipid-to-DNA charge ratio,  [Rädler
1998].
Abb.7 Schematic phase diagram. The one-phase region corresponds to isoelectric lamellar
complexes. In the two neighboring regimes complexes coexist with either DNA or lipid.
(drawing after ref.Harries 1998]).
6
3.2 The lamellar-hexagonal transition
DOPE
The lamellar-hexagonal transition as a function of the mol-percentage of the
ethanolamine lipids DOPE. The plot depicts the evolution of the DNA lattice constant
[Koltover 1998].
3.3 Thermotropic Phasebehavior
L  Drd  L  Drd
L
‘
Tm
L
d DNA
dL
Gel-liquid-crystalline phase transition of the lipid chains (left).
DMPC/DMTAP-DNA (right)
7
Phase diagramm of
4.1 Poisson-Boltzmann-and counter ion release
:
.
dDNA
m
w
AD
+
Na Cl
AL
Cross section of the lipid-DNA stacks.
The cationic lipids are laterally mobil
and can be regarded as twodimensionally bound counterlipids.
2
1 u(x,z ) 1 
 2u(x,z) 
H A B
 K 
2  z  2  x 2 
2
Fluctuating lattice of semiflexible rods in two dimensions.
8
The melting of the lamellar columnar phase
Sequence of lamellar phases as a function of temperature or coupling parameter
a) lamellar-columnar b) lamellar-sliding c) lamellar-nematic d) lamellar-isotropic.
X-ray scattering pattern of a partially oriented film. The reflexes of the DNA superlattice
are broadened due to thermal fluctuations of the DNA lattice. [Artzner 1999]
9
norm. frequency
Transfection and implications for gene therapy
Cationic Lipid
0.1
none
Alveo
Exo
0.01
0.001
0
200
400
600
radius of gyration [nm]
Dendritic aggregated lipid-DNA complexes close to the isoelectric ratio (scale bar=10µm).
The size distribution can be determined by quantitative fluorescence microscopy. The
distribution function follows an exponential law.
cationic
liposomes
DNA
1
2
fusion
endocytosis
3
Golgi
ER
4
nucleus
Path of entry of cationic lipid- DNA gene delivery complexes. Complexes
are taken up by endocytosis, fuse with the endosome and are released
into the cytosol.
10
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