Biophysical Journal
Volume 104, Issue 11, 4 June 2013, Pages 2456-2464
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Article
Kinesin-8 Is a Low-Force Motor Protein with a Weakly Bound Slip State

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Abstract

During the cell cycle, kinesin-8s control the length of microtubules by interacting with their plus ends. To reach these ends, the motors have to be able to take many steps without dissociating. However, the underlying mechanism for this high processivity and how stepping is affected by force are unclear. Here, we tracked the motion of yeast (Kip3) and human (Kif18A) kinesin-8s with high precision under varying loads using optical tweezers. Surprisingly, both kinesin-8 motors were much weaker compared with other kinesins. Furthermore, we discovered a force-induced stick-slip motion: the motor frequently slipped, recovered from this state, and then resumed normal stepping motility without detaching from the microtubule. The low forces are consistent with kinesin-8s being regulators of microtubule dynamics rather than cargo transporters. The weakly bound slip state, reminiscent of a molecular safety leash, may be an adaptation for high processivity.

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Volker Bormuth’s present address is Institut Curie, Paris, France.

Erik Schäffer’s present address is Center for Plant Molecular Biology (ZMBP), University of Tübingen, Tübingen, Germany.