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SYNF: Symposium Nonlinear and Fractional Transport in Complex Systems

SYNF 1: Nonlinear and Anomalous Transport in Complex Systems

SYNF 1.1: Invited Talk

Wednesday, March 28, 2007, 14:45–15:15, H1

Depolymerization of microtubules by kinesins — •Jonathon Howard — Max Planck Institute of Molecular Cell Biology & Genetics, Dresden

The kinesin superfamily are proteins with sequence similarity to the motor domain of kinesin-1, the founding member of the superfamily. Many kinesins, including kinesin-1, are motors that couple the chemical potential associated with the hydrolysis of ATP into mechanical force used to drive directed movement along a microtubule. However, cellular and genetic studies indicate that kinesins in several of the families destabilize microtubules. For example, deleting kinesin-8 leads to longer mitotic spindles, and overexpressing kinesin-13 leads to loss of cytoplasmic microtubules. To determine how destabilization occurs, we have developed single-molecule-fluorescence assays to study directly the interaction of these kinesins with microtubules. We have discovered that both kinesin are depolymerases that bind to microtubule ends and depolymerize them in an ATP-dependent manner. Kinesin-13 and kinesin-8 target to the ends by different mechanisms. Kinesin-13 uses a diffusion and capture mechanism to quickly and economically reach either end. By contrast, kinesin-8 is a highly processive and directed motor that depolymerizes longer microtubules more quickly than shorter ones, providing a feedback mechanism that can account for the role of kinesin-8 in regulating spindle size. These single-molecule studies demonstrate that kinesin proteins are not just transporters but also regulate the polymerization of the track itself.