DNA condensation in two dimensions

Abstract

We have found that divalent electrolyte counterions common in biological cells (Ca(2+), Mg(2+), and Mn(2+) ) can condense anionic DNA molecules confined to two-dimensional cationic surfaces. DNA-condensing agents in vivo include cationic histones and polyamines spermidine and spermine with sufficiently high valence (Z) 3 or larger. In vitro studies show that electrostatic forces between DNA chains in bulk aqueous solution containing divalent counterions remain purely repulsive, and DNA condensation requires counterion valence Z >/= 3. In striking contrast to bulk behavior, synchrotron x-ray diffraction and optical absorption experiments show that above a critical divalent counterion concentration the electrostatic forces between DNA chains adsorbed on surfaces of cationic membranes reverse from repulsive to attractive and lead to a chain collapse transition into a condensed phase of DNA tethered by divalent counterions. This demonstrates the importance of spatial dimensionality to intermolecular interactions where nonspecific counterion-induced electrostatic attractions between the like-charged polyelectrolytes overwhelm the electrostatic repulsions on a surface for Z = 2. This new phase, with a one-dimensional counterion liquid trapped between DNA chains at a density of 0.63 counterions per DNA bp, represents the most compact state of DNA on a surface in vitro and suggests applications in high-density storage of genetic information and organo-metallic materials processing.

Strongly correlated electrostatics of viral genome packaging

“…It is due to this unique setup of the bacteriophage where DNA is pre-packaged by a motor protein during virus assembly that Mg +2 ions can induce attractions between DNA. It should be mentioned that Mg +2 counterions have been shown experimentally to condense DNA in another confined system: the DNA condensation in two dimension [25]. Results from our computer simulations in Section 5 (see also [26,27]), also show that if the lateral motion of DNA is restricted, divalent counterions can induced DNA condensation.…”

The structural diversity of DNA–neutral phospholipids–divalent metal cations aggregates: a small-angle synchrotron X-ray diffraction study

“…As a consequence, the lamellar repeat distance changes resulting in a compression (or swelling) of the lamellar stack (Dan, 1996;Dan, 1997;Harries et al, 2003;May and Ben Shaul, 2004). Indeed, X -ray diffraction data Koltover et al, 1999;Zantl et al, 1999;Koltover et al, 2000;Uhríková et al, 2002;Uhríková et al, 2004) analysis of the line shape of the DNA peak suggests a 2D smectic order of strands with crosscorrelations between the DNA strands of adjacent layers Salditt et al, 1998). Double stranded DNA is a rigid rod-like molecule showing negligible flexibility.…”

Phase Behavior of DPPC in a DNA−Calcium−Zwitterionic Lipid Complex Studied by Small-Angle X-ray Scattering

“…We would also expect to find them in our complex since calcium is known to cause DNA condensation when confined to a surface, specifically in a complex with cationic lipids. 40 Since both lipid phases are present in each of the SAXS patterns observed, any DNA peaks which may occur are probably obscured or masked by the peaks arising from the two lipid phases. DNA peaks usually observed in cationic lipoplexes are weak in comparison to the lipid peaks.…”