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Vol. 17, Issue 2, 700-710, February 2006

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Full-Length Dimeric MCAK Is a More Efficient Microtubule Depolymerase than Minimal Domain Monomeric MCAK

Kathleen M. Hertzer ^*, Stephanie C. Ems-McClung ^*, Susan L. Kline-Smith ^* , Thomas G. Lipkin ^* , Susan P. Gilbert , and Claire E. Walczak ^*

^* Medical Sciences Program, Indiana University, Bloomington, IN 47405; Department of Biological Sciences, University of Pittsburgh, Pittsburgh, PA 15260

Submitted August 31, 2005; Revised November 2, 2005; Accepted November 7, 2005
Monitoring Editor: Tim Stearns

MCAK belongs to the Kinesin-13 family, whose members depolymerize microtubules rather than translocate along them. We defined the minimal functional unit of MCAK as the catalytic domain plus the class specific neck (MD-MCAK), which is consistent with previous reports. We used steady-state ATPase kinetics, microtubule depolymerization assays, and microtubule·MCAK cosedimentation assays to compare the activity of full-length MCAK, which is a dimer, with MD-MCAK, which is a monomer. Full-length MCAK exhibits higher ATPase activity, more efficient microtubule end binding, and reduced affinity for the tubulin heterodimer. Our studies suggest that MCAK dimerization is important for its catalytic cycle by promoting MCAK binding to microtubule ends, enhancing the ability of MCAK to recycle for multiple rounds of microtubule depolymerization, and preventing MCAK from being sequestered by tubulin heterodimers.

The online version of this article contains supplemental material at MBC Online (http://www.molbiolcell.org).

Present addresses: Ludwig Institute for Cancer Research, University of California, San Diego, La Jolla, CA 92093

Present addresses: Department of Anatomy and Cell Biology, Columbia University Medical Center, New York, NY 10032.

Address correspondence to: Claire E. Walczak (cwalczak{at}indiana.edu).

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