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.

The rate of microtubule breaking increases exponentially with curvature.

Microtubules, cylindrical assemblies of tubulin proteins with a 25 nm diameter and micrometer lengths, are a central part of the cytoskeleton and also serve as building blocks for nanobiodevices. Microtubule breaking can result from the activity of severing enzymes and mechanical stress. Breaking can lead to a loss of structural integrity, or an increase in the numbers of microtubules.

Age and Sex Differences in Load-Induced Tibial Cortical Bone Surface Strain Maps.

Bone adapts its architecture to the applied load; however, it is still unclear how bone mechano-adaptation is coordinated and why potential for adaptation adjusts during the life course. Previous animal models have suggested strain as the mechanical stimulus for bone adaptation, but yet it is unknown how mouse cortical bone load-related strains vary with age and sex. In this study, full-field strain maps (at 1 N increments up to 12 N) on the bone surface were measured in young, adult, and old (aged 10, 22 weeks, and 20 months, respectively), male and female C57BL/6J mice with load applied using a noninvasive murine tibial model.

Microtubule Detachment in Gliding Motility Assays Limits the Performance of Kinesin-Driven Molecular Shuttles.

The creation of complex active nanosystems integrating cytoskeletal filaments propelled by surface-adhered motor proteins often relies on the filaments' ability to glide over up to meter-long distances. While theoretical considerations support this ability, we show that microtubule detachment (either spontaneous or triggered by a microtubule crossing event) is a non-negligible phenomenon that has been overlooked until now. The average gliding distance before spontaneous detachment was measured to be 30 ± 10 mm for a functional kinesin-1 density of 500 μm and 9 ± 4 mm for a functional kinesin-1 density of 100 μm at 1 mM ATP.

Assembling Molecular Shuttles Powered by Reversibly Attached Kinesins.

This protocol describes how to create kinesin-powered molecular shuttles with a weak and reversible attachment of the kinesins to the surface. In contrast to previous protocols, in this system, microtubules recruit kinesin motor proteins from solution and place them on a surface. The kinesins will, in turn, facilitate the gliding of the microtubules along the surface before desorbing back into the bulk solution, thus being available to be recruited again.

Aldolase Does Not Show Enhanced Diffusion in Dynamic Light Scattering Experiments.

Recent experimental studies have measured a 30-80% increase of the diffusion coefficient when various enzymes, including aldolase, are catalytically active. This observation has been supported by several theoretical explanations; however, other theoretical studies argue against the possibility of enhanced diffusion, and two of them ascribe the experimental observations to potential artifacts arising in fluorescence correlation spectroscopy (FCS) measurements. Here, we utilized dynamic light scattering (DLS) to measure the diffusion coefficient of aldolase in the absence and presence of its substrate.