Structure of self-assembled liposome-DNA-metal complexes

Abstract

We have studied the structural and morphological properties of the triple complex dioleoyl phosphatidylcholine (DOPC)-DNA-Mn2+ by means of synchrotron x-ray diffraction and freeze-fracture transmission electron microscopy. This complex is formed in a self-assembled manner when water solutions of neutral lipid, DNA, and metal ions are mixed, which represents a striking example of supramolecular chemistry. The DNA condensation in the complex is promoted by the metal cations that bind the polar heads of the lipid with the negatively charged phosphate groups of DNA. The complex is rather heterogeneous with respect to size and shape and exhibits the lamellar symmetry of the L(c)(alpha) phase: the structure consists of an ordered multilamellar assembly similar to that recently found in cationic liposome-DNA complexes, where the hydrated DNA helices are sandwiched between the liposome bilayers. The experimental results show that, at equilibrium, globules of the triple complex in the L(c)(alpha) phase coexist with globules of multilamellar vesicles of DOPC in the L(alpha) phase, the volume ratio of the two structures being dependent on the molar ratio of the three components DOPC, DNA, and Mn2+. These complexes are of potential interest for applications as synthetically based nonviral carriers of DNA vectors for gene therapy.

The structural diversity of DNA–neutral phospholipids–divalent metal cations aggregates: a small-angle synchrotron X-ray diffraction study

“…3) (see also Uhríková et al, 2002;2005a). Our short analysis indicates no marked (Francescangeli et al, 2003) and also in the liquid -crystalline phase of DPPC : DNA=8 : 1 (mol/base) aggregates at 1 -100 mM Ca 2+ (McManus et al, 2003b), where mechanism of interaction and models of coexistence of both phases were proposed. Our previous work (Uhríková et al, 2005a) documents that such structure forms also DOPC + DNA in a wide range of cations concentrations (0 -76.5 mM of Ca 2+ or Mg 2+ ).…”

“…For DPPC:DNA=8:1 mol/base aggregates formed in presence of 1-100 mM CaCl 2 , the coexistence of two lamellar phases was reported (McManus et al, 2003a, b), one with DNA strands intercalated in the water layer between lipid bilayers with a repeat distance d~8.0-7.4 nm and another one with a repeat distance d~6.6-5.6 nm, which was interpreted as a phase formed by lipid bilayers only. Francescangeli et al (2003) observed also the coexistence of two lamellar phases in aggregates of DOPC+DNA+Mn 2+ . The coexistence of two lamellar phases in one aggregate formed by DOPC+DNA in the concentration range 0-76.5 mM of metal cations (Ca 2+ or Mg 2+ ), effect of temperature, DOPC:DNA molar ratio, and length of DNA fragments were studied in our recently published work (Uhríková et al, 2005a).…”

Observation of a Rectangular Columnar Phase in a DNA−Calcium−Zwitterionic Lipid Complex

“…Structural studies of both the cationic and zwitterionic DNA lipoplexes have been reported over the past number of years. [4][5][6][13][14][15][16][17][18][19][20][21] However, here we show for the first time that, in addition to the enhanced divalent cation binding, 17 this complex is capable of arranging DNA into higher orders of local organization.The complex is prepared by mixing DNA (calf thymus, purified by a method described before 18 ), unilamellar liposomes of DPPC, prepared by bath sonication at 50°C, and calcium from concentrated stocks in the wide part of a 1 mm X-ray capillary. The complex was allowed to form for 1 h before being centrifuged to the end of the capillary and equilibrated by a cycle of heating and cooling, above and below the melt transition temperature of the lipid over a number of days.…”

“…Structural studies of both the cationic and zwitterionic DNA lipoplexes have been reported over the past number of years. [4][5][6][13][14][15][16][17][18][19][20][21] However, here we show for the first time that, in addition to the enhanced divalent cation binding, 17 this complex is capable of arranging DNA into higher orders of local organization.…”

“…However, complexes composed entirely of natural, zwitterionic lipid can complex with DNA when the interaction is mediated by a divalent cation. [9][10][11][12][13][14] Complexes formed by neutral lipids in the absence of the divalent cation have also been described. 15,16 The divalent cation-lipid complexes are entirely noncytotoxic and thereby have a remarkable status among the candidate systems in that the binding is highly tunable.…”