Active matter
How do motors make microtubule bundles stretch?
Open access · cc by · source: Europe PMC
Adding a crowding agent packs microtubules more tightly and changes how the filaments move inside a bundle, even though the bundle as a whole keeps stretching.
Study at a glance
- Design
- Other — In vitro active-matter experiments on reconstituted microtubule-kinesin-14 bundles across PEG depletant concentrations, with photobleaching, single-filament tracking and small-angle X-ray scattering plus scattering-model fits.
- N
- No single sample count reported; many bundles and tracer filaments were analysed per PEG concentration.
- Population
- Reconstituted bundles of stabilized microtubules driven by kinesin-14 motors with 0-1% PEG
- Outcome
- Bleach-line splitting and extension speeds, tracer velocity statistics, and bundle packing lattice from SAXS
Structured fields used in claim comparison tables when every cited study has a complete layer.
Key findings
Bundles extended along their length and thinned across it at all PEG levels, but the overall extension speed fell from about 8.8 to about 4.5 nm per second as PEG rose. Without PEG each bleached stripe split into two lines moving apart, showing antiparallel sliding, whereas at 1% PEG stripes only broadened; intermediate concentrations showed a mix. Scattering fits indicated open hexagonal packing with about 45.8 nm spacing without PEG, and a tight rectangular lattice at 1% PEG.
Methodology
The authors mixed stabilized microtubules with kinesin-14 motors, which both crosslink and slide filaments, and varied the concentration of the crowding polymer PEG between none and 1%. They photobleached pairs of stripes on bundles to watch how filaments moved apart, tracked rare fluorescently labelled tracer microtubules, and used small-angle X-ray scattering compared with computed scattering curves to infer how filaments were packed.
Limitations
The experiments do not show where the motors actually sit inside the bundles, so the idea that tight packing excludes motors from the interior is speculation. The scattering fits use lattices of fewer than ten microtubules and peaks are broad, meaning the packing has only short-range order. The expected exponential (telescoping) extension could not be distinguished from linear growth over the short distances measured, and a faster net extension despite mostly sliding motion at low PEG remains unexplained.
How this study connects
Role on claims
Each row is a claim on a concept or method page where this paper supports, challenges, or qualifies the statement. Roles are hand-checked — not a model guess.
Crowding changes both the packing and the way motor-driven bundles move.
In reconstituted microtubule-kinesin-14 bundles, adding PEG depletant roughly halved extension speed (about 8.8 to 4.5 nm/s), switched motion from antiparallel sliding to broadening, and changed X-ray-inferred packing from open hexagonal to a tight rectangular lattice.
Evidence for the claim as stated.
Evidence spans very different systems (electrokinetic colloids, biological filaments on membranes or at oil-water interfaces, centimetre-scale robots), each studied in one geometry, so no single paper tests whether a mechanism carries across systems.
Evidence for the claim as stated.
Open questions
Tensions this paper is part of
From concept pages' “where studies disagree.” Disagreement means the same question; scope means different assays, populations, or outcomes.
Evidence spans very different systems (electrokinetic colloids, biological filaments on membranes or at oil-water interfaces, centimetre-scale robots), each studied in one geometry, so no single paper tests whether a mechanism carries across systems.
Related papers in this topic
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