bioRxiv | 2021
Motor processivity and speed determine structure and dynamics of microtubule-motor assemblies
Abstract
Active matter systems can generate highly ordered structures, avoiding equilibrium through the consumption of energy by individual constituents. How the microscopic parameters that characterize the active agents are translated to the observed mesoscopic properties of the assembly has remained an open question. These active systems are prevalent in living matter; for example, in cells, the cytoskeleton is organized into structures such as the mitotic spindle through the coordinated activity of many motor proteins walking along microtubules. Here, we investigate how the microscopic motor-microtubule interactions affect the coherent structures formed in a reconstituted motor-microtubule system. We explore key parameters experimentally and theoretically, using a variety of motors with different speeds, processivities, and directionalities. We demonstrate that aster size depends on the motor used to create the aster, and develop a model for the distribution of motors and microtubules in steady-state asters that depends on parameters related to motor speed and processivity. Further, we show that network contraction rates scale linearly with the single-motor speed in quasi one-dimensional contraction experiments. Finally, we demonstrate that competition between motors of opposite polarity can be tuned to create various structures. In all, this theoretical and experimental work helps elucidate how microscopic motor properties are translated to the much larger scale of collective motor-microtubule assemblies. 1 Significance In living matter, the consumption of energy at the molecular scale often results in the emergence of ordered structures that are hundreds to thousands of times greater in size. A canonical system for studying the emergence of ordered structures is the cellular cytokeleton, which primarily consists of filaments and motor proteins. Here, we use a recently developed optogenetically controlled motormicrotubule system to explore the relation between the properties of the motors that interact with microtubules, each with its own average velocity and processivity, and the structures that emerge when those motors act collectively to form asters. We find that aster size, distribution of motors within the aster, and inter-aster contraction rates are connected to these motor properties.