Kinesin steps do not alternate in size
Adrian Fehr 1, Charles Asbury 2 and Steven Block 3*
1 Stanford
2 Univ. Washington
3 Stanford University
* To whom correspondence should be addressed. E-mail: sblock{at}stanford.edu.
Submitted on October 16, 2007
Revised on November 29, 2007
Accepted on 14 December 2007
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Abstract |
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Kinesin is a two-headed motor protein that transports cargo inside cells by moving stepwise on microtubules. Its exact trajectory along the microtubule is unknown: alternative pathway models predict either uniform 8 nm steps or alternating 7- and 9 nm-sized steps. By analyzing single-molecule stepping traces from "limping" kinesin molecules, we were able to distinguish alternate fast- and slow-phase steps and thereby to calculate the step sizes associated with the motions of each of the two heads. We also compiled step distances from non-limping kinesin molecules and compared these distributions against models predicting uniform or alternating step sizes. In both cases, we find that kinesin takes uniform 8 nm steps, a result that strongly constrains the allowed models.
Key Words:
laser tweezers, motility, optical trap, optical tweezers
