Sasha Zemsky

All Publications

• Motor crosslinking augments elasticity in active nematics. Soft matter Redford, S. A., Colen, J., Shivers, J. L., Zemsky, S., Molaei, M., Floyd, C., Ruijgrok, P. V., Vitelli, V., Bryant, Z., Dinner, A. R., Gardel, M. L. 2024

  Abstract

  In active materials, uncoordinated internal stresses lead to emergent long-range flows. An understanding of how the behavior of active materials depends on mesoscopic (hydrodynamic) parameters is developing, but there remains a gap in knowledge concerning how hydrodynamic parameters depend on the properties of microscopic elements. In this work, we combine experiments and multiscale modeling to relate the structure and dynamics of active nematics composed of biopolymer filaments and molecular motors to their microscopic properties, in particular motor processivity, speed, and valency. We show that crosslinking of filaments by both motors and passive crosslinkers not only augments the contributions to nematic elasticity from excluded volume effects but dominates them. By altering motor kinetics we show that a competition between motor speed and crosslinking results in a nonmonotonic dependence of nematic flow on motor speed. By modulating passive filament crosslinking we show that energy transfer into nematic flow is in large part dictated by crosslinking. Thus motor proteins both generate activity and contribute to nematic elasticity. Our results provide new insights for rationally engineering active materials.

  View details for DOI 10.1039/d3sm01176c

  View details for PubMedID 38385209

• Exploitation of Engineered Light-Switchable Myosin XI for Nanotechnological Applications. ACS nano Salhotra, A., Rahman, M. A., Ruijgrok, P. V., Meinecke, C. R., Ušaj, M., Zemsky, S., Lindberg, F. W., Surendiran, P., Lyttleton, R. W., Linke, H., Korten, T., Bryant, Z., Månsson, A. 2023

  Abstract

  For certain nanotechnological applications of the contractile proteins actin and myosin, e.g., in biosensing and network-based biocomputation, it would be desirable to temporarily switch on/off motile function in parts of nanostructured devices, e.g., for sorting or programming. Myosin XI motor constructs, engineered with a light-switchable domain for switching actin motility between high and low velocities (light-sensitive motors (LSMs) below), are promising in this regard. However, they were not designed for use in nanotechnology, where longevity of operation, long shelf life, and selectivity of function in specific regions of a nanofabricated network are important. Here, we tested if these criteria can be fulfilled using existing LSM constructs or if additional developments will be required. We demonstrated extended shelf life as well as longevity of the actin-propelling function compared to those in previous studies. We also evaluated several approaches for selective immobilization with a maintained actin propelling function in dedicated nanochannels only. Whereas selectivity was feasible using certain nanopatterning combinations, the reproducibility was not satisfactory. In summary, the study demonstrates the feasibility of using engineered light-controlled myosin XI motors for myosin-driven actin transport in nanotechnological applications. Before use for, e.g., sorting or programming, additional work is however needed to achieve reproducibility of the nanofabrication and, further, optimize the motor properties.

  View details for DOI 10.1021/acsnano.3c05137

  View details for PubMedID 37639711

• Design and characterization of optically controllable filamentous myosins Zemsky, S., Ruijgrok, P. V., Bryant, Z. CELL PRESS. 2022: 292A

  View details for Web of Science ID 000759523001683

• Optical control of fast and processive engineered myosins in vitro and in living cells. Nature chemical biology Ruijgrok, P. V., Ghosh, R. P., Zemsky, S. n., Nakamura, M. n., Gong, R. n., Ning, L. n., Chen, R. n., Vachharajani, V. T., Chu, A. E., Anand, N. n., Eguchi, R. R., Huang, P. S., Lin, M. Z., Alushin, G. M., Liphardt, J. T., Bryant, Z. n. 2021

  Abstract

  Precision tools for spatiotemporal control of cytoskeletal motor function are needed to dissect fundamental biological processes ranging from intracellular transport to cell migration and division. Direct optical control of motor speed and direction is one promising approach, but it remains a challenge to engineer controllable motors with desirable properties such as the speed and processivity required for transport applications in living cells. Here, we develop engineered myosin motors that combine large optical modulation depths with high velocities, and create processive myosin motors with optically controllable directionality. We characterize the performance of the motors using in vitro motility assays, single-molecule tracking and live-cell imaging. Bidirectional processive motors move efficiently toward the tips of cellular protrusions in the presence of blue light, and can transport molecular cargo in cells. Robust gearshifting myosins will further enable programmable transport in contexts ranging from in vitro active matter reconstitutions to microfabricated systems that harness molecular propulsion.

  View details for DOI 10.1038/s41589-021-00740-7

  View details for PubMedID 33603247

• Spatiotemporal control of liquid crystal structure and dynamics through activity patterning. Nature materials Zhang, R. n., Redford, S. A., Ruijgrok, P. V., Kumar, N. n., Mozaffari, A. n., Zemsky, S. n., Dinner, A. R., Vitelli, V. n., Bryant, Z. n., Gardel, M. L., de Pablo, J. J. 2021

  Abstract

  Active materials are capable of converting free energy into mechanical work to produce autonomous motion, and exhibit striking collective dynamics that biology relies on for essential functions. Controlling those dynamics and transport in synthetic systems has been particularly challenging. Here, we introduce the concept of spatially structured activity as a means of controlling and manipulating transport in active nematic liquid crystals consisting of actin filaments and light-sensitive myosin motors. Simulations and experiments are used to demonstrate that topological defects can be generated at will and then constrained to move along specified trajectories by inducing local stresses in an otherwise passive material. These results provide a foundation for the design of autonomous and reconfigurable microfluidic systems where transport is controlled by modulating activity with light.

  View details for DOI 10.1038/s41563-020-00901-4

  View details for PubMedID 33603187

• Optical Control of Fast and Processive Engineered Myosins In Vitro and in Living Cells Ruijgrok, P. V., Ghosh, R. P., Nakamura, M., Zemsky, S., Chen, R., Vachharajani, V., Liphardt, J. T., Bryant, Z. CELL PRESS. 2019: 259A

  View details for DOI 10.1016/j.bpj.2018.11.1410

  View details for Web of Science ID 000460779801296