microtubule self-assembly is controlled by the topological activity of ring and linear DNA in microtubule-DNA composites*

Polymer composites, ubiquitous in biological systems, display complex behaviors influenced by the topology of their constituent components. For example, we previously found that the polymerization of tubulin into microtubules was markedly suppressed when embedded in an entangled solution of ring DNA, whereas the same concentration of linear DNA led to enhanced polymerization and flocculation of microtubules, resulting in a non-monotonic dependence of composite stiffness on tubulin concentration. Here, we investigate the time-dependent structural and mechanical properties of similar DNA-microtubule composites, undergoing in situ enzymatically-driven linearization and fragmentation of DNA rings, to determine the impact of DNA digestion on the self-assembly of the microtubule network. We use Optical Tweezers integrating Differential Dynamic Microscopy (OpTiDMM) to measure the time-dependent rheological properties and couple rheology to the changing structure and dynamics of the microtubules and DNA in the networks. Our preliminary results indicate that in situ topological conversion significantly alters the structural evolution of the microtubule networks, with DNA fragmentation promoting flocculation at a rate controlled by the enzyme stoichiometry. This topologically-active composite demonstrates a novel approach to controlling the kinetics of network self-assembly, as well as the initial and final mechanical and structure states, by performing topological operations on the surrounding polymers.