Interaction of short-fragmented DNA with dipalmitoylphosphatidylcholine bilayers in presence of zinc

Abstract

The structure and temperature behaviour of the DNA+dipalmitoylphosphatidylcholine (DPPC) bilayer as a function of ZnCl 2 concentration were examined using differential scanning calorimetry (DSC), small-angle neutron scattering (SANS) and small-angle X-ray diffraction (SAXD). Experiments revealed the coexistence of two lamellar phases in the mixture: the L PC phase, formed due to Zn 2+ binding to the DPPC bilayers, and the condensed lamellar phase L DNA+PC with DNA strands packed between the DPPC bilayers. With increasing concentration of zinc, the temperature of the gel -liquid-crystal phase transition of DPPC increases in both phases, and the volume fraction of L DNA+PC phase decreases. In the gel state (at 20°C), the repeat distance of L DNA+PC phase is constant, d DNA+PC ~ 8.3 nm, up to 20 mmol/l of ZnCl 2 , and increases for higher concentrations of the salt. The periodicity of the L PC lamellar phase decreases substantially with the increasing concentration of the salt in the mixture. In the liquid-crystalline state, concentrations above 20 mmol/l ZnCl 2 promote the dissolution of the L DNA+PC phase into DPPC + Zn 2+ unilamellar vesicles and DNA is neutralized by Zn 2+ ions. The screening of Zn 2+ charge and the formation of a diffuse double layer due to increasing ionic strength of solution are responsible for the observed changes.

Lipid bilayer – DNA interaction mediated by divalent metal cations: SANS and SAXD study

“…Thus at higher zinc concentrations, binding sites of both, DNA and DPPC are saturated, and zinc does not mediate the binding. This saturation is responsible for the macroscopic phase separation observed in the studied mixtures, and the temperature instability of DNA + DPPC + Zn 2+ phase particularly in aggregates with short fragmented DNA as shown in [15,40].…”

“…This indicates a destruction of the lamellar structure yielding its swelling into excess of water. The periodicity of the L V phase is modulated with increasing concentration of zinc (Table 1) that was studied in [15]. We believe that only a fraction of lipid is bound by DNA and Zn 2+ forming L C phase, the rest of DPPC forms L V phase, which shows the periodicity decreasing with increasing concentration of ions in solution, and which is macroscopically separated from L C .…”

“…In this contribution we demonstrate the structural differences in aggregates prepared due to DNA interaction with DPPC bilayer in the presence of calcium and zinc observed in our SAXD experiments. We have studied recently polymorphic behaviour of the DNA-DPPC in a solution of divalent transition metals and Zn 2+ in large concentration range [7,15]. In aggregates with phosphatidylcholines (DPPC, DMPC, DOPC), we have identified structures: L C -condensed lamellar phase; L X -lamellar phase with DNA strands intercalated between the adjacent lipid bilayers, without regular packing; coexistence of a lamellar phase L PC of pure lipid with L X or L C phase.…”

“…SAXD diffractograms (at 20 o C) of: Is=122 mM)*The peak related to the DNA-DNA packing is marked by arrow. Is is ionic strength of solution * adapted from[15].…”

Membrane Morphology Modifications Induced by Hydroquinones

“…3 A wealth of information is available in the literature concerning the thermal phase transitions occurring in these systems 4À6 and also about the influence of other components, 7 such as additives 8 and ionic strength of the environment. 9 Moreover, theoretical models dealing with bilayer stability 10 and structural aspects of phase transitions have been proposed and are continuously being revised.…”