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J. Biol. Chem., Vol. 283, Issue 4, 2078-2087, January 25, 2008

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Getting in Sync with Dimeric Eg5

INITIATION AND REGULATION OF THE PROCESSIVE RUN^*

From the Department of Biological Sciences, University of Pittsburgh, Pittsburgh, Pennsylvania 15260

Eg5/KSP is the kinesin-related motor protein that generates the major plus-end directed force for mitotic spindle assembly and dynamics. Recent work using a dimeric form of Eg5 has found it to be a processive motor; however, its mechanochemical cycle is different from that of conventional Kinesin-1. Dimeric Eg5 appears to undergo a conformational change shortly after collision with the microtubule that primes the motor for its characteristically short processive runs. To better understand this conformational change as well as head-head communication during processive stepping, equilibrium and transient kinetic approaches have been used. By contrast to the mechanism of Kinesin-1, microtubule association triggers ADP release from both motor domains of Eg5. One motor domain releases ADP rapidly, whereas ADP release from the other occurs after a slow conformational change at 1 s^-1. Therefore, dimeric Eg5 begins its processive run with both motor domains associated with the microtubule and in the nucleotide-free state. During processive stepping however, ATP binding and potentially ATP hydrolysis signals rearward head advancement 16 nm forward to the next microtubule-binding site. This alternating cycle of processive stepping is proposed to terminate after a few steps because the head-head communication does not sufficiently control the timing to prevent both motor domains from entering the ADP-bound state simultaneously.

Received for publication, October 9, 2007 , and in revised form, November 20, 2007.

^* This work was supported by NIGMS Grant R01-GM54141 from the National Institutes of Health (to S. P. G.), NIAMS Career Development Award K02-AR47841 from the National Institutes of Health and Department of Health and Human Services (to S. P. G.), and Starter Grant MCB-0722724 from the National Science Foundation (to M. G.). The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.

The on-line version of this article (available at http://www.jbc.org) contains supplemental Figs. S1–S3.

¹ To whom correspondence should be addressed: Dept. of Biology, Rensselaer Polytechnic Institute, Troy, NY 12180-3590. Tel.: 518-276-4415; Fax: 518-276-2851; E-mail: sgilbert{at}rpi.edu.

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