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

Abstract

Complexes composed of DNA and cationic lipids have been studied in detail in recent years, mainly due to their potential to deliver DNA to cells in gene therapy. 1 It has been recognized that different structures can be prepared, based on these compositions and lipid chemistry. In this communication, we give the first example of a higher-order arrangement of DNA within an entirely noncytotoxic complex.This opens the pathway to explore the consequences of such ordering on the issue of delivery and other arenas where DNA arrays may have biological significance. We believe such nontoxic ordered arrays of DNA may in the future represent novel components of structural and functional significance at the interface of the "synthetic biology" endeavor. 2 Until now most studies on these synthetic systems have been done with the focus of creating artificial devices for gene delivery. In these cases, some researchers have screened large numbers of different lipid-DNA formulations to identify successful candidates in vitro. 3 Others, however, have tried to understand the complexes on a more fundamental level, studying structure, phase behavior, and other physical characteristics, in the hope that this would ultimately enable a "design"-based approach to delivery, 4-8 but no systematic understanding has emerged.However, we consider that there emerges a general role for the engineering of ordered arrays of DNA that can protect the DNA in a biological environment but which is easily manipulated to provide compact readable and addressable devices. Such complexes typically cannot be based on direct electrostatic interaction between cationic lipids and DNA, as these are quite cytotoxic and the degree of binding is ill-controlled after initial preparation. 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. They have been studied less, possibly due to the erroneous assumption that the interaction between divalent cations and zwitterionic lipids is weak. We have shown previously that the complex forms over a number of calcium concentrations. 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 t...

Molecular Recognition Drives Oligonucleotide Binding to Nucleolipid Self‐Assemblies

“…The observed time evolution demands a study on longer timescales to investigate the formation of ordered structures of nucleolipoplexes; the formation of ordered DNA-calcium-zwitterionic-lipid complexes has, for instance, been found to proceed through longterm incubation at 277 K. [15] After storage at 277 K for a week, the sample of diC 8 PA/ polyU shows a precipitate that is not present in the control systems (that is, polyU, diC 8 PU/polyU, and diC 8 PA). Figure 6 shows the SAXS spectrum of the precipitate, obtained after the storage.…”

Molecular dynamics study of structure and vibrational spectra at zwitterionoic lipid/aqueous KCl, NaCl, and CaCl2 solution interfaces

“…In particular, the specific interaction of cations near the bilayer headgroups has a strong effect on the structure, dynamics, and stability of the membranes. [1][2][3] For example, the concentration of intracellular Ca 2+ has recently been recognized to play key roles in some biological processes, such as membrane fusion, [4][5][6] DNA-zwitterionic lipid association, [7][8][9] and the regulation of cell death (necrosis, apoptosis, and autophagy). 10 In addition to the divalent cation, monovalent ions such as K + and Na + with its counter anion Cl are also present in biological membranes and affect the physical properties of membrane.…”

Self‐Assembly Structure Formation during the Digestion of Human Breast Milk

“…Lamellar structures with similar dimensions have been previously reported in mixtures of DNA and DPPC in the presence of CaCl 2 , all components of human breast milk. [29] After 14 minutes, Bragg reflections of the discontinuous micellar cubic (Fd3m type) phase grew at q = 0.071, 0.117, 0.142, 0.165, 0.179, 0.200 À1 . The lattice constant of the Fd3 m phase decreased slightly during the digestion from 157 to 153 .…”