Why kinesin is so processive
Edited by Edwin W. Taylor, Northwestern University Feinberg School of Medicine, Chicago, IL, and approved June 16, 2009
Abstract
Kinesin I can walk on a microtubule for distances as long as several micrometers. However, it is still unclear how this molecular motor can remain attached to the microtubule through the hundreds of mechanochemical cycles necessary to achieve this remarkable degree of processivity. We have addressed this issue by applying ensemble and single-molecule fluorescence methods to study the process of kinesin stepping, and our results lead to 4 conclusions. First, under physiologic conditions, ≈75% of processively moving kinesin molecules are attached to the microtubule via both heads, and in this conformation, they are resistant to dissociation. Second, the remaining 25% of kinesin molecules, which are in an “ATP waiting state” and are strongly attached to the microtubule via only one head, are intermittently in a conformation that cannot bind ATP and therefore are resistant to nucleotide-induced dissociation. Third, the forward step in the kinesin ATPase cycle is very fast, accounting for <5% of the total cycle time, which ensures that the lifetime of this ATP waiting state is relatively short. Finally, by combining nanometer-level single-molecule fluorescence localization with higher ATP concentrations than used previously, we have determined that in this ATP waiting state, the ADP-containing head of kinesin is located 8 nm behind the attached head, in a location where it can interact with the microtubule lattice. These 4 features reduce the likelihood that a kinesin I motor will dissociate and contribute to making this motor so highly processive.
Acknowledgments.
We thank Marileen Dogterom for sharing the step finder program; Ben Blehm, Comert Kural, Evan Graves, Hasan Yardimci, Sultan Doganay, Sheyum Syed, and Tyler Lougheed for helpful discussions; and Trine Giaever for producing Fig. 5. This work was supported by National Institutes of Health Grants GM068625 (to P.R.S.) and AR048565 (to S.S.R.) and National Science Foundation Frontiers Grant 0822613 (to P.R.S).
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Cover image: Pictured is a microbial mat growing near White Creek in Yellowstone National Park. These microbial communities produce lipids with unusually large variations in their deuterium content. Zhang et al. show that such variations likely relate to the different metabolic pathways employed by the microbes and suggest that deuterium variations in ancient lipids could be used to identify pathways of energy metabolism active in the past. See the Feature Article by Xinning Zhang et al. on pages 12580–12586. Image by Alex Sessions.
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© 2009.
Submission history
Received: August 27, 2008
Published online: August 4, 2009
Published in issue: August 4, 2009
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Acknowledgments
We thank Marileen Dogterom for sharing the step finder program; Ben Blehm, Comert Kural, Evan Graves, Hasan Yardimci, Sultan Doganay, Sheyum Syed, and Tyler Lougheed for helpful discussions; and Trine Giaever for producing Fig. 5. This work was supported by National Institutes of Health Grants GM068625 (to P.R.S.) and AR048565 (to S.S.R.) and National Science Foundation Frontiers Grant 0822613 (to P.R.S).
Notes
This article is a PNAS Direct Submission.
This article contains supporting information online at www.pnas.org/cgi/content/full/0808396106/DCSupplemental.
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The authors declare no conflict of interest.
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