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Kinesin follows the microtubule's protofilament axis
S Ray1, E Meyhöfer, R A Milligan
1Department of Physiology and Biophysics, University of Washington, Seattle 98195.
Abstract:
We tested the hypothesis that kinesin moves parallel to the microtubule's protofilament axis. We polymerized microtubules with protofilaments that ran either parallel to the microtubule's long axis or that ran along shallow helical paths around the cylindrical surface of the microtubule. When gliding across a kinesin-coated surface, the former microtubules did not rotate. The latter microtubules, those with supertwisted protofilaments, did rotate; the pitch and handedness of the rotation accorded with the supertwist measured by electron cryo-microscopy. The results show that kinesin follows a path parallel to the protofilaments with high fidelity. This implies that the distance between consecutive kinesin-binding sites along the microtubule must be an integral multiple of 4.1 nm, the tubulin monomer spacing along the protofilament, or a multiple of 8.2 nm, the dimer spacing.
Insights
Kinesin motors move along microtubules by following protofilament paths. This precise movement dictates specific spacing between kinesin-binding sites on the microtubule structure.
Area of Science:
- Cellular biology
- Biophysics
- Molecular motors
Background:
- Kinesin is a motor protein that transports cargo within cells along microtubule tracks.
- The precise path kinesin takes along microtubules is crucial for understanding intracellular transport mechanisms.
- Microtubules are composed of protofilaments, whose arrangement can influence motor protein movement.
Purpose of the Study:
- To test the hypothesis that kinesin moves parallel to the microtubule's protofilament axis.
- To determine if microtubule protofilament structure dictates kinesin's movement path.
- To investigate the implications of kinesin's path for kinesin-binding site spacing.
Main Methods:
- Polymerization of microtubules with distinct protofilament orientations (parallel vs. helical).
- Observing microtubule gliding on kinesin-coated surfaces.
- Measuring microtubule rotation, pitch, and handedness using electron cryo-microscopy.
- Analyzing the relationship between protofilament supertwist and observed rotation.
Main Results:
- Microtubules with parallel protofilaments did not rotate when gliding on kinesin.
- Microtubules with helical (supertwisted) protofilaments exhibited rotation.
- The observed rotation pitch and handedness correlated with the protofilament supertwist.
- Kinesin demonstrated high-fidelity movement along the protofilament axis.
Conclusions:
- Kinesin motor proteins move with high fidelity along the microtubule protofilament axis.
- This precise movement implies that kinesin-binding sites on microtubules are spaced at integral multiples of 4.1 nm or 8.2 nm.
- The findings provide critical insights into the molecular mechanism of kinesin-microtubule interaction.