DNA Phase Transition in Charge Neutralization and Comformation Induced by Trivalent-Hydrolysed Metal Ions

Abstract

Abstract:It is well known that common trivalent counter ions can induce DNA compaction or condensation but are unable to invert DNA surface charge in a normal aqueous solution. In the present study, we found that trivalent-hydrolysed metal ions (Fe 3+ , Al 3+ ) are not only capable of inducing DNA condensation, but they also invert the electrophoretic mobility of DNA by electrophoretic light scattering and single molecular techniques. In comparison with neutral trivalent cations, hydrolysed metal ions such as Fe 3+ can induce DNA condensation at a much lower concentration of cations, and its corresponding morphology of condensed DNA was directly observed by atomic force microscopy (AFM). The condensing and unravelling forces of DNA condensates were measured by tethering DNA by magnetic tweezers (MT) measurements at various concentration of Fe 3+ and Al 3+ . We found that a coil-globule transition of DNA by hydrolysed metal ions not only was observed in DNA-complex sizes, but also in the curve of electrophoretic mobility of DNA in solution. In contrast, the transition was not observed in the case of neutral trivalent cations such as La 3+ and Co 3+ . We attribute the transition and charge inversion to the ion-specific interaction between hydrolysed metal ions and phosphates of DNA backbone.

Phase transition of DNA compaction in confined space: Effects of macromolecular crowding are dominant*

“…DNA compaction, as for its biological importance [1,2] and the challenges to the current understanding of semiflexible polymers, [3][4][5] has become the focus of many investigations, [6][7][8][9][10][11] in which a series of single molecule experiments concentrated on the dynamics of DNA compaction caused by multivalent counterions that the multivalent cationdependent DNA toroid folded or unfolded step by step under tension, [6][7][8][9][10][11] the charge reversion in DNA compaction process [12,13] which has strong influences on the compaction by modulating the barrier for condensate nucleation, and the DNA compaction mediated by divalent counterions at different PH values. [14,15] Concurrently, polyethylene glycol (PEG), bovine serum albumin (BSA) and dextran were used as crowders to mimic the macromolecular crowding in different confinement [16][17][18] and their effects on the complex phase transition of DNA compaction have been investigated thoroughly.…”