Polymorphism of DNA-anionic liposome complexes reveals hierarchy of ion-mediated interactions

Hongjun Liang, Daniel Harries, Gerard C.L. Wong*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

69 Scopus citations

Abstract

Self-assembled DNA delivery systems based on anionic lipids (ALs) complexed with DNA mediated by divalent cations have been recently introduced as an alternative to cationic lipid-DNA complexes because of their low cytotoxicity. We investigate AL-DNA complexes induced by different cations by using synchrotron small angle x-ray scattering and confocal microscopy to show how different ion-mediated interactions are expressed in the self-assembled structures and phase behavior of AL-DNA complexes. The governing interactions in AL-DNA systems are complex: divalent ions can mediate strong attractions between different combinations of the components (such as DNA-DNA and membrane-membrane). Moreover, divalent cations can coordinate nonelectrostatically with lipids and modify the resultant membrane structure. We find that at low membrane charge densities AL-DNA complexes organize into a lamellar structure of alternating DNA and membrane layers crosslinked by ions. At high membrane charge densities, a new phase with no analog in cationic lipid-DNA systems is observed: DNA is expelled from the complex, and a lamellar stack of membranes and intercalated ions is formed. For a subset of the ionic species, high ion concentrations generate an inverted hexagonal phase comprised of DNA strands wrapped by ion-coated lipid tubes. A simple theoretical model that takes into account the electrostatic and membrane elastic contributions to the free energy shows that this transition is consistent with an ion-induced change in the membrane spontaneous curvature, c0. Moreover, the crossover between the lamellar and inverted hexagonal phases occurs at a critical C0 that agrees well with experimental values.

Original languageAmerican English
Pages (from-to)11173-11178
Number of pages6
JournalProceedings of the National Academy of Sciences of the United States of America
Volume102
Issue number32
DOIs
StatePublished - 9 Aug 2005
Externally publishedYes

Keywords

  • Colloids
  • Like-charge attraction
  • Membrane
  • Self-assembly
  • X-ray

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