title: Protein friction limits diffusive and directed movements of kinesin motors on microtubules.
abstract: 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.
authors.affiliation: Max Planck Institute of Molecular Cell Biology and Genetics, Pfotenhauerstrasse 108, 01307 Dresden, Germany.
authors.forename: Volker
authors.initials: V
authors.lastname: Bormuth
authors.forename: Vladimir
authors.initials: V
authors.lastname: Varga
authors.forename: Jonathon
authors.initials: J
authors.lastname: Howard
authors.forename: Erik
authors.initials: E
authors.lastname: Schäffer
mesh_terms: D000244:Adenosine Diphosphate / Q000378:metabolism; D000255:Adenosine Triphosphate / Q000378:metabolism; D055598:Chemical Phenomena; D004058:Diffusion; D017276:Friction; D016547:Kinesins; D008863:Microspheres; D008869:Microtubule-Associated Proteins / Q000737:chemistry* / Q000378:metabolism; D008870:Microtubules / Q000378:metabolism*; D020409:Molecular Motor Proteins / Q000737:chemistry* / Q000378:metabolism; D052898:Optical Tweezers; D011993:Recombinant Fusion Proteins / Q000737:chemistry / Q000378:metabolism; D029701:Saccharomyces cerevisiae Proteins / Q000737:chemistry* / Q000378:metabolism; D013816:Thermodynamics
chemical_list: C108256:KIP3 protein, S cerevisiae; D008869:Microtubule-Associated Proteins; D020409:Molecular Motor Proteins; D011993:Recombinant Fusion Proteins; D029701:Saccharomyces cerevisiae Proteins; D000244:Adenosine Diphosphate; D000255:Adenosine Triphosphate; D016547:Kinesins