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Science 14 August 2009:
Vol. 325. no. 5942, pp. 870 - 873
DOI: 10.1126/science.1174923
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Reports

Protein Friction Limits Diffusive and Directed Movements of Kinesin Motors on Microtubules

Volker Bormuth,1 Vladimir Varga,1 Jonathon Howard,1,* Erik Schäffer2,*

Friction limits the operation of macroscopic engines and is critical to the performance of micromechanical devices. We report measurements of friction in a biological nanomachine. Using optical tweezers, we characterized the frictional drag force of individual kinesin-8 motor proteins interacting with their microtubule tracks. At low speeds and with no energy source, the frictional drag was related to the diffusion coefficient by the Einstein relation. At higher speeds, the frictional drag force increased nonlinearly, consistent with the motor jumping 8 nanometers between adjacent tubulin dimers along the microtubule, and was asymmetric, reflecting the structural polarity of the microtubule. We argue that these frictional forces arise from breaking bonds between the motor domains and the microtubule, and they limit the speed and efficiency of kinesin.

1 Max Planck Institute of Molecular Cell Biology and Genetics, Pfotenhauerstrasse 108, 01307 Dresden, Germany.
2 Nanomechanics Group, Biotechnology Center, TU Dresden, Tatzberg 47-51, 01307 Dresden, Germany.

* To whom correspondence should be addressed. E-mail: Howard{at}mpi-cbg.de(J.H.); Erik.Schaeffer{at}biotec.tu-dresden.de(E.S.)

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THIS ARTICLE HAS BEEN CITED BY OTHER ARTICLES:
Friction in Motor Proteins.
C. Veigel and C. F. Schmidt (2009)
Science 325, 826-827
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