Reentrant behavior of divalent counterion mediated DNA-DNA electrostatic interaction

TL;DR

This study uses computer simulations to reveal that divalent counterions can induce DNA reentrant condensation under restricted configurational entropy, showing complex electrostatic interactions similar to higher-valent ions.

Contribution

It demonstrates for the first time that divalent counterions can cause DNA reentrant condensation when DNA configurational entropy is limited, expanding understanding of electrostatic DNA interactions.

Findings

DNA-DNA interaction is strongly repulsive at low or high divalent ion concentrations.

At intermediate concentrations, the interaction is negligible or slightly attractive.

Divalent counterions can induce DNA condensation similar to higher-valent ions under certain conditions.

Abstract

The problem of DNA-DNA interaction mediated by divalent counterions is studied using computer simulation. Although divalent counterions cannot condense free DNA molecules in solution, we show that if DNA configurational entropy is restricted, divalent counterions can cause DNA reentrant condensation similar to that caused by tri- or tetra-valent counterions. DNA-DNA interaction is strongly repulsive at small or large counterion concentration and is negligible or slightly attractive for a concentration in between. Implications of our results to experiments of DNA ejection from bacteriophages are discussed. The quantitative result serves to understand electrostatic effects in other experiments involving DNA and divalent counterions.