[Show abstract][Hide abstract] ABSTRACT: The structure of aggregates formed due to DNA interaction with
dipalmitoylphosphatidylcholine (DPPC) in presence of Ca2+ and
Zn2+ is examined using small-angle synchrotron X-ray
diffraction (SAXD) and small-angle neutron scattering (SANS). SAXD
detected two structures: LC - condensed lamellar phase and
LX - lamellar phase with DNA strands intercalated between the
adjacent lipid bilayers, without regular packing at low cation
concentration (~1 mM). The high concentration of Zn2+ induces
a macroscopic phase separation in mixtures. The SANS curves of
DPPC+ions2+ vesicles evaluated using the strip function model
have shown different modes of cations binding to the DPPC bilayers.
Journal of Physics Conference Series 03/2012; 351(1):2011-.
[Show abstract][Hide abstract] ABSTRACT: We studied the effect of divalent alkaline earth metal cations Ca²⁺, Mg²⁺ and transition metals Co²⁺, Ni²⁺, Cu²⁺ and Zn²⁺ on DNA condensation and its protection against thermal denaturation in presence of dioleoylphosphatidylcholine liposomes (DOPC). Experimental results have shown that Ca²⁺ and Mg²⁺ as well as Zn²⁺ mediate DNA condensation. Cu²⁺ causes DNA double helix destabilization, and does not mediate binding between DNA and DOPC liposomes. Co²⁺ and Ni²⁺ can interact with DNA on both ways mentioned above. Static light scattering was use to follow the size of aggregates in DNA condensation process. Phospholipid bilayer and divalent cations protect condensed DNA against thermal destabilization. The highest stabilization effect was found in aggregates with Ca²⁺ and Zn²⁺, whereas in presence of either Co²⁺ or Ni²⁺ some volume fraction of DNA is denatured.
[Show abstract][Hide abstract] ABSTRACT: We investigate the structure of aggregates formed due to DNA interaction with saturated neutral phosphatidylcholines [dipalmitoylphosphatidylcholine (DPPC) and dimyristoylphosphatidylcholine] in presence of Ca(2+) and Mg(2+) cations using simultaneous synchrotron small- and wide-angle X-ray diffractions. For DPPC:DNA = 3:1 mol/base and in the range of 1-50 mM Ca(2+), the diffractograms show structural heterogeneity of aggregates. We observe the coexistence of two lamellar phases in aggregates prepared at 1 mM Ca(2+): L(x) phase with the DNA strands (of unknown organization) intercalated in water layers between adjacent lipid bilayers and L(DPPC) phase of DPPC bilayers without any divalent cations and DNA strands. Aggregates prepared in the range 2-50 mM Ca(2+) show a condensed gel lamellar phase L (g) (c) with the lipid bilayer periodicity d approximately 8.0 nm, and the DNA-DNA interhelical distance d (DNA) approximately 5.1 nm. The increase of temperature induces the decrease in the intensity and the increase in the width of the DNA related peak. In the fluid state, the condensed lamellar phase L (alpha) (c) gradually converts into L(x) phase. The aggregates do not exhibit rippled P(beta) phase. The thermal behaviour of aggregates was investigated in the range 20-80 degrees C. Applying heating-cooling cycles, the aggregates converted into energetically more favourable structure: a condensed lamellar phase L(c) (or L(x)) is preserved or we observe lateral segregation of the DNA strands and metal cations (L(x) phase) in coexistence with L(PC) phase of pure phospholipids.
European Biophysics Journal 05/2007; 36(4-5):363-75. · 2.47 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Dipalmitoylphosphatidylcholine (DPPC) was hydrated in 0.2–60 mM solution of CaCl2 in heavy water and thoroughly homogenized by freezing-thawing process. Small-angle neutron scattering (SANS) shows formation of unilamellar vesicles in the range 1–60 mM of CaCl2. From the Kratky–Porod plot ln [I(Q)Q2] vs. Q2 of SANS intensity I(Q) in the range of scattering vectors Q corresponding to the interval 0.001 Å−2≤Q2≤0.006 Å−2, the vesicle bilayer radius of gyration Rg and the bilayer thickness parameter dg were obtained. The structure of the bilayer displays different behavior for the gel phase and the liquid-crystalline phase: In the gel phase (at 20°C), the values of dg indicate nonlinear changes in the lipid bilayer thickness, with a maximum at ~5 mM CaCl2. In the liquid-crystalline phase (at 60°C), the parameter of the lipid bilayer thickness dg=43.2±0.3 Å is constant within the concentration range 1≤cCa≤40 mM. Vesicles prepared at 60 mM CaCl2 show within experimental error, the same values of dg as pure DPPC unilamellar vesicles prepared by extrusion using polycarbonate filter with pores of diameter 500 Å.