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Bead movement by single kinesin molecules studied with optical tweezers
S M Block1, L S Goldstein, B J Schnapp
1Rowland Institute for Science, Cambridge, Massachusetts 02142.
Nature
|November 22, 1990
Summary
Kinesin, a motor protein, powers movement by briefly detaching from microtubules during its cycle. This study used optical tweezers to observe kinesin
Area of Science:
- Cell Biology
- Biophysics
- Molecular Motors
Background:
- Kinesin is a crucial mechanoenzyme responsible for intracellular transport, converting chemical energy from ATP hydrolysis into mechanical force for movement along microtubules.
- Understanding the precise mechanochemical cycle of kinesin is vital for elucidating the mechanisms underlying various cellular processes, including vesicle transport.
Purpose of the Study:
- To investigate the binding and detachment dynamics of individual kinesin molecules interacting with microtubules.
- To differentiate between models of kinesin's mechanochemical cycle, specifically whether it remains bound to the microtubule throughout the cycle or detaches transiently.
Main Methods:
- Utilized a single-beam gradient-force optical particle trap (optical tweezers) to precisely manipulate microscopic silica beads coated with kinesin.
- Attached beads to microtubules and observed their movement and detachment dynamics at low kinesin concentrations (approximately 0.17-3 molecules per bead).
- Applied optical forces to the beads to assess their detachment from microtubules under different binding conditions (e.g., AMP.PNP-induced rigor linkage).
Main Results:
- Individual kinesin molecules exhibited transient detachment from microtubules during their mechanochemical cycle, leading to limited movement (average 1.4 microns) and spontaneous release.
- Beads propelled by multiple kinesin molecules or under rigor conditions showed stable microtubule attachment, unlike those with few kinesin molecules.
- Optical tweezers could readily detach beads with low kinesin occupancy, suggesting a dynamic binding-release mechanism.
Conclusions:
- The experimental findings support a model where kinesin detaches from the microtubule during its mechanochemical cycle.
- This transient detachment mechanism is fundamental to kinesin's processive movement and force generation.
- The study provides critical insights into the molecular mechanisms of microtubule-based motility.