Microrheology of topologically-active DNA solutions

DNA naturally exists in three distinct topologies - supercoiled, relaxed circular, and linear - with enzymes that convert one topology to another. Changes to DNA topology can give rise to changes in the viscoelastic properties of dense DNA solutions. Thus, topological conversion of DNA offers a way to design active biopolymer solutions that can alter their rheological properties in programmable ways. Here, we create highly entangled solutions of DNA molecules that actively undergo enzyme-driven conversion from supercoiled to linear topology over the course of several hours. We perform time-resolved particle-tracking microrheology during the conversion to examine how changes in topology affect the viscoelastic properties of DNA solutions in real-time. We show that these ‘topologically active' biopolymer solutions exhibit time-dependent non-equilibrium dynamics and viscoelasticity that can be tuned by the concentration of the constituents. For example, solutions undergo viscous thickening as molecules convert from supercoiled to linear topology. In future work, we will examine different DNA lengths, concentrations, topologies, and enzymatic activities to create a class of programmable topologically active materials.