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J. Biol. Chem., Vol. 277, Issue 47, 44980-44987, November 22, 2002

This Article Full Text Full Text (PDF) All Versions of this Article: 277/47/44980    most recent M207758200v1 Submit a Letter to Editor Alert me when this article is cited Alert me when eLetters are posted Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Request Permissions Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Wiethoff, C. M. Articles by Middaugh, C. R. Search for Related Content PubMed PubMed Citation Articles by Wiethoff, C. M. Articles by Middaugh, C. R. Social Bookmarking                      What's this?

The Structural Organization of Cationic Lipid-DNA Complexes^*

Christopher M. Wiethoff^§, Michelle L. Gill^¶, Gary S. Koe, Janet G. Koe, and C. Russell Middaugh^**

From the  Department of Pharmaceutical Chemistry, The University of Kansas, Lawrence, Kansas 66047 and  Valentis, Inc., Burlingame, California 94010

The interaction of cationic liposomes with supercoiled plasmid DNA results in a major rearrangement of each component to form compact multilamellar structures comprised of alternating layers of two-dimensional arrays of DNA sandwiched between lipid bilayers. Fluorescence resonance energy transfer was used to estimate the distance of closest approach of DNA to the lipid bilayers in these complexes. The effect of several compositional variables on this distance, including the ratio of cationic lipid to DNA, and the charge density, intrinsic curvature, and fluidity of the lipid bilayer were examined. Additionally, the effect of ionic strength was studied. For complexes prepared at or above a 3:1 charge ratio (+/), the observed distance of closest approach was found to be in agreement with the intercalation of DNA between lipid bilayers. As the charge ratio was decreased, a monotonic increase in the distance was observed with a maximum observed at 0.5:1. Correlations between differences in the proximity of DNA to the lipid bilayer and the hydrodynamic size of the complexes were also found. A model based on these observations and previous reports suggests the formation of discrete populations of complexes below a charge ratio of 0.5:1 and above 3:1. The structure of the negatively charged complexes is consistent with DNA extending from the surface of the particles, whereas those possessing excess positive charge were multilamellar aggregates with the DNA effectively condensed between lipid bilayers. Complexes between these two states consist of weighted fractions of these two species.

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