Regulation of Biomolecular-Motor-Driven Cargo Transport by Microtubules under Mechanical Stress

Microtubule Deformation Modulates Intracellular Transport by Kinesin Differently Than Dynein

Mechanical stress on cells is transmitted through many biological processes, for example, cell shape control, tissue patterning, and axonal homeostasis. Microtubules, a cytoskeletal component, presumably play a significant role in the mechanoregulation of cellular processes. We investigate motor protein-driven transport of quantum dots along mechanically deformed microtubules. We found that microtubule deformation significantly slowed kinesin-driven transport, whereas we previously reported dynein-driven transport was rather robust. Such dualistic modulation of transportation dynamics of the motor proteins by microtubule deformation can be attributed to the altered affinity of the motor proteins for buckled microtubules. Our results may form the basis for understanding microtubules' role in regulating cellular processes in a mechanically adverse environment through its detection ability and response to mechanical stress.

Mechanical fatigue in microtubules

Mechanical failure of biological nanostructures due to sustained force application has been studied in great detail. In contrast, fatigue failure arising from repeated application of subcritical stresses has received little attention despite its prominent role in engineering and potentially biology. Here, paclitaxel-stabilized microtubules are up to 256 times bent into sinusoidal shapes of varying wavelength and the frequency of breaking events are observed. These experiments allow the calculation of fatigue life parameters for microtubules. Repeated buckling due to 12.5% compression-equal to the compression level experienced by microtubules in contracting cardiomyocytes - results in failure after in average 5 million cycles, whereas at 20.0% compression failure occurs after in average one thousand cycles. The fatigue strength (Basquin) exponent B is estimated as - 0.054±0.009.

Tensile Stress on Microtubules Facilitates Dynein-Driven Cargo Transport

Mechanical stress significantly affects the physiological functions of cells, including tissue homeostasis, cytoskeletal alterations, and intracellular transport. As a major cytoskeletal component, microtubules respond to mechanical stimulation by altering their alignment and polymerization dynamics. Previously, we reported that microtubules may modulate cargo transport by one of the microtubule-associated motor proteins, dynein, under compressive mechanical stress. Despite the critical role of tensile stress in many biological functions, how tensile stress on microtubules regulates cargo transport is yet to be unveiled. The present study demonstrates that the low-level tensile stress-induced microtubule deformation facilitates dynein-driven transport. We validate our experimental findings using all-atom molecular dynamics simulation. Our study may provide important implications for developing new therapies for diseases that involve impaired intracellular transport.

In Vitro Synthesis and Design of Kinesin Biomolecular Motors by Cell-Free Protein Synthesis

Kinesin is a biomolecular motor that generates force and motility along microtubule cytoskeletons in cells. Owing to their ability to manipulate cellular nanoscale components, microtubule/kinesin systems show great promise as actuators of nanodevices. However, classical in vivo protein production has some limitations for the design and production of kinesins. Designing and producing kinesins is laborious, and conventional protein production requires specific facilities to create and contain recombinant organisms. Here, we demonstrated the in vitro synthesis and editing of functional kinesins using a wheat germ cell-free protein synthesis system. The synthesized kinesins propelled microtubules on a kinesin-coated substrate and showed a higher binding affinity with microtubules than E. coli-produced kinesins. We also successfully incorporated affinity tags into the kinesins by extending the original sequence of the DNA template by PCR. Our method will accelerate the study of biomolecular motor systems and encourage their wider use in various nanotechnology applications.

Cargo Transport by Microtubule-Associated Motor Protein Along Mechanically Deformed Microtubules

Mechanical forces play pivotal roles in regulating various cellular functions. Biomolecular motor protein-driven intracellular transportation is one example which is affected by mechanical forces, although the mechanism at molecular level is unknown. In this chapter, we describe deformation of microtubules under compressive stress and we show that such deformation of microtubules affects the kinetics of dynein-driven cargo transportation along the microtubules. The extent of alteration in the kinetics of dynein-driven transportation is found strongly dependent on the extent of deformation of microtubules under compressive stress.

Mechanical Deformation of Microtubules on a Two-Dimensional Elastic Medium

Microtubule, the most rigid filamentous protein in cytoskeleton, plays significant roles in cellular mechano-transduction and mechano-regulation of cellular functions. In cells, the mechanical stress serves as a prevalent stimulus to frequently cause deformation of the microtubules participating in various cellular events. While the experimental and simulation-based approaches have confirmed the role of mechanical stress to tune mechanical properties of microtubule. Yet, the effect of mechanical force on the structural stability and the mechanism of microtubule deformation have remained obscure. Here, we describe the mechanical stress-induced deformation of microtubules using a custom-made mechanical device. We designed the device in a way which allows the microtubules to undergo deformation as response to the applied stress while attached on a two-dimensional elastic substrate through interaction with microtubule-associated motor protein, kinesin. We provide here the method to cause controlled bucking or fragmentation of microtubules by applying compressive or tensile stress on the microtubules, respectively. Such study is crucial to understand the mechanism of deformation in microtubules in cellular environment and their consequences in physiological activities.

Deformation of microtubules regulates translocation dynamics of kinesin

Microtubules, the most rigid components of the cytoskeleton, can be key transduction elements between external forces and the cellular environment. Mechanical forces induce microtubule deformation, which is presumed to be critical for the mechanoregulation of cellular events. However, concrete evidence is lacking. In this work, with high-speed atomic force microscopy, we unravel how microtubule deformation regulates the translocation of the microtubule-associated motor protein kinesin-1, responsible for intracellular transport. Our results show that the microtubule deformation by bending impedes the translocation dynamics of kinesins along them. Molecular dynamics simulation shows that the hindered translocation of kinesins can be attributed to an enhanced affinity of kinesins to the microtubule structural units in microtubules deformed by bending. This study advances our understanding of the role of cytoskeletal components in mechanotransduction.