MD vs AFM on supercoiled DNA

In the cell, DNA is arranged into highly-organised and topologically-constrained (supercoiled) structures. It remains unclear how this supercoiling affects the double-helical structure of DNA, largely because of limitations in spatial resolution of the available biophysical tools. Here, we overcome these limitations by a combination of atomic force microscopy (AFM) and atomistic molecular dynamics (MD) simulations, to resolve structures of negatively-supercoiled DNA minicircles at base-pair resolution. We observe that negative superhelical stress induces local variation in the canonical B-form DNA structure by introducing kinks and defects that affect global minicircle structure and flexibility. We probe how these local and global conformational changes affect DNA interactions through the binding of triplex-forming oligonucleotides to DNA minicircles. We show that the energetics of triplex formation is governed by a delicate balance between electrostatics and bonding interactions. Our results provide mechanistic insight into how DNA supercoiling can affect molecular recognition of diverse conformational substrates.

High-resolution AFM images and snapshots from MD simulations on natively supercoiled DNA minicircles

ALB Pyne, A Noy*, K Main, V Velasco-Berrelleza, MM Piperakis, LA Mitchenall, FM Cugliandolo, JG Beton, CEM Stevenson, BW Hoogenboom, AD Bates, A Maxwell, SA Harris (2020). “Base-pair resolution analysis of the effect of supercoiling on DNA flexibility and major groove recognition by triplex-forming oligonucleotides” bioRxiv.

In this article, we have also designed SerraLINE, a program to calculate bending angles from simulated DNA structures and mirror them with AFM.

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