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The structural organization of cationic lipid-DNA complexes
Christopher M Wiethoff1, Michelle L Gill, Gary S Koe
1Department of Pharmaceutical Chemistry, The University of Kansas, Lawrence, Kansas 66047, USA.
The Journal of Biological Chemistry
|September 26, 2002
Summary
Cationic liposomes and DNA form compact structures. DNA intercalation between lipid bilayers depends on the charge ratio, influencing complex size and structure.
Area of Science:
- Biophysical Chemistry
- Materials Science
- Molecular Biology
Background:
- Cationic liposomes are widely used for gene delivery.
- Understanding DNA-lipid interactions is crucial for optimizing delivery systems.
- The structural organization of DNA-lipid complexes influences their efficacy.
Purpose of the Study:
- To investigate the structural rearrangements of cationic liposomes and DNA.
- To determine the effect of compositional variables on DNA proximity to lipid bilayers.
- To elucidate the structural basis of DNA-lipid complex formation.
Main Methods:
- Complex formation between cationic liposomes and supercoiled plasmid DNA.
- Fluorescence resonance energy transfer (FRET) to measure DNA-lipid distances.
- Systematic variation of lipid composition and ionic strength.
Main Results:
- Compact multilamellar structures with alternating DNA and lipid layers were formed.
- DNA intercalation between lipid bilayers was observed at charge ratios ≥ 3:1.
- Decreasing charge ratio increased DNA-lipid distance, with maximum separation at 0.5:1.
- Hydrodynamic size correlated with DNA proximity to lipid bilayers.
Conclusions:
- Complex structure is dependent on the cationic liposome to DNA charge ratio.
- Excess positive charge leads to multilamellar aggregates with intercalated DNA.
- Excess negative charge results in DNA extending from the particle surface.
- A model describing discrete complex populations was proposed.