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J. Biol. Chem., Vol. 281, Issue 49, 37782-37793, December 8, 2006

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Kinetic and Mechanistic Basis of the Nonprocessive Kinesin-3 Motor NcKin3^*

Sarah Adio¹, Marieke Bloemink, Michaela Hartel, Sven Leier, Michael A. Geeves, and Günther Woehlke²

From the Institute for Cell Biology, Ludwig-Maximilians-University Munich, Schillerstrasse 42, D-80336 Munich, Germany and Department of Biosciences, University of Kent, Canterbury CT2 7NJ, United Kingdom

Kinesin-3 motors have been shown to transport cellular cargo along microtubules and to function according to mechanisms that differ from the conventional hand-over-hand mechanism. To find out whether the mechanisms described for Kif1A and CeUnc104 cover the full spectrum of Kinesin-3 motors, we characterize here NcKin3, a novel member of the Kinesin-3 family that localizes to mitochondria of ascomycetes. We show that NcKin3 does not move in a K-loop-dependent way as Kif1A or in a cluster-dependent way as CeUnc104. Its in vitro gliding velocity ranges between 0.30 and 0.64 µm/s and correlates positively with motor density. The processivity index (k_bi,ratio) of 3 reveals that not more than three ATP molecules are hydrolyzed per productive microtubule encounter. The NcKin3 duty ratio of 0.03 indicates that the motor spends only a minute fraction of the ATPase cycle attached to the filament. Unlike other Kinesin-3 family members, NcKin3 forms stable dimers, but only one subunit releases ADP in a microtubule-dependent fashion. Together, these data exclude a processive hand-over-hand mechanism of movement and suggest a power-stroke mechanism where nucleotide-dependent structural changes in a single motor domain lead to displacement of the motor along the filament. Thus, NcKin3 is the first plus end-directed kinesin motor that is dimeric but moves in a nonprocessive fashion to its destination.

Received for publication, May 26, 2006 , and in revised form, August 24, 2006.

^* The work was supported in part by the Deutsche Forschungsgemeinschaft Grants SFB 413 and SPP 1068 and the Friedrich-Baur Stiftung. 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 Methods, Figs. S1-S4, and Refs. 1 and 2.

¹ Participant in the EMBO Workshop Transient Kinetic Methods Applied to Biological Macromolecules.

² To whom correspondence should be addressed. Tel.: 49-89-2180-75889; Fax: 49-89-2180-75882; E-mail: guenther.woehlke{at}lrz.uni-muenchen.de.

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