I. Koltover et al., AN INVERTED HEXAGONAL PHASE OF CATIONIC LIPOSOME-DNA COMPLEXES RELATED TO DNA RELEASE AND DELIVERY, Science, 281(5373), 1998, pp. 78-81
A two-dimensional columnar phase in mixtures of DNA complexed with cat
ionic liposomes has been found in the Lipid composition regime known t
o be significantly more efficient at transfecting mammalian cells in c
ulture compared to the lamellar (L-alpha(subset of)) structure of cati
onic liposome-DNA complexes. The structure, derived from synchrotron x
-ray diffraction, consists of DNA coated by cationic lipid monolayers
and arranged on a two-dimensional hexagonal lattice (H-parallel to(sub
set of)). Two membrane-altering pathways induce the L-alpha(subset of)
--> H-parallel to(subset of) transition: one where the spontaneous cu
rvature of the Lipid monolayer is driven negative, and another where t
he membrane bending rigidity is lowered with a new class of helper-lip
ids. Optical microscopy revealed that the L-alpha(subset of) complexes
bind stably to anionic vesicles (models of cellular membranes), where
as the more transfectant H-parallel to(subset of) complexes are unstab
le and rapidly fuse and release DNA upon adhering to anionic vesicles.