Structural Rigidity of Paranemic (PX) and Juxtapose (JX) DNA Nanostructures

TL;DR

This study uses atomistic molecular dynamics simulations to quantify the mechanical rigidity of paranemic (PX) and juxtapose (JX) DNA nanostructures, revealing their higher stiffness compared to B-DNA and the influence of ionic conditions.

Contribution

It provides the first direct quantitative assessment of the mechanical strength of crossover DNA motifs, informing the design of more rigid DNA nanostructures.

Findings

PX and JX DNA have ~30% higher stretch modulus than B-DNA.

Divalent Mg2+ ions increase rigidity due to electrostatic screening.

Rigidity varies with ionic environment, affecting nanostructure stability.

Abstract

Crossover motifs are integral components for designing DNA based nanostructures and nanomechanical devices due to their enhanced rigidity compared to the normal B-DNA. Although the structural rigidity of the double helix B-DNA has been investigated extensively using both experimental and theoretical tools, to date there is no quantitative information about structural rigidity and the mechanical strength of parallel crossover DNA motifs. We have used fully atomistic molecular dynamics simulations in explicit solvent to get the force-extension curve of parallel DNA nanostructures to characterize their mechanical rigidity. In the presence of mono-valent Na+ ions, we find that the stretch modulus (\gamma_1) of the paranemic crossover (PX) and its topo-isomer JX DNA structure is significantly higher (~ 30%) compared to normal B-DNA of the same sequence and length. However, this is in contrast to the original expectation that these motifs are almost twice rigid compared to the double-stranded B-DNA. When the DNA motif is surrounded by a solvent with Mg2+ counterions, we find an enhanced rigidity compared to Na+ environment due to the electrostatic screening effects arising from the divalent nature of Mg2+ ions. This is the first direct determination of the mechanical strength of these crossover motifs which can be useful for the design of suitable DNA for DNA based nanostructures and nanomechanical devices with improved structural rigidity.