Topological Tuning of DNA Mobility in Entangled Solutions of Supercoiled Plasmids

Ring polymers in dense solutions are among the most intriguing problems in
polymer physics. Thanks to its natural occurrence in circular form, DNA has
been extensively employed as a proxy to study the fundamental physics of ring
polymers in different topological states. Yet, torsionally constrained – such
as supercoiled – topologies have been largely neglected so far. The applicability
of existing theoretical models to dense supercoiled DNA is thus unknown.
Here we address this gap by coupling large-scale Molecular Dynamics simulations
with Differential Dynamic Microscopy of entangled supercoiled DNA
plasmids. We discover that, unexpectedly, larger supercoiling increases the
size of entangled plasmids and concomitantly induces an enhancement in DNA
mobility. These findings are reconciled as due to supercoiling-driven asym-metric and double-folded plasmid conformations which reduce inter-plasmids
entanglements and threadings. Our results suggest a way to topologically tune
DNA mobility via supercoiling, thus enabling topological control over the (micro)
rheology of DNA-based complex fluids.