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Stefan Diez

Biophysics of single motors and collective effects in multi-motor transport

We use optical single molecule imaging and tracking techniques to learn about the interaction of biomolecular motors with their filaments [1]. While the stepping behavior of single kinesin-1 motor proteins has been studied in great detail, in cells, these motors often do not work alone but rather function in small groups when they transport cellular cargo. Performing in vitro gliding motility assays where MTs coated with quantum dots were driven over a glass surface by a known number of kinesin-1 motors, we investigate whether two or more motors that move the same cargo step in synchrony (producing the same step size as a single motor) or whether the step size of the cargo movement varies [2]. Besides kinesin-1, there is a vast number of motors which biophysical principles remain to be deciphered. Among those is the mitotic centromere associated kinesin (MCAK, kinesin-13) which binds to the end of a microtubule and contributes to the fast depolymerization of these filaments in the presence of ATP [3, 4].

Movement of single GFP-tagged kinesin-1 molecules (green) along surface bound microtubules (red). The timelapse movie was acquired using TIRF microscopy with 2 frames per second.

Tracking the motion of quantum dot-coated microtubules driven by a known number of motors [2]. In the case of transport by two kinesin-1 motors, we found successive 4-nm steps, corresponding to half the step size of a single motor. The existence of these fractional steps illustrates a lack of synchronization and has implications for the analysis of motor-driven organelle movement investigated in vivo.

GFP-MCAK molecules (green) bound to surface-immobilized mircotubules (red). While the MCAK molecules are predominantly found at the end of the microtubules, they are also transiently present on the microtubule lattice. We hypothesize, that one-dimensional diffusion along the lattice constitutes one means of accelerated microtubule end targeting for individual MCAK molecules [3, 4].


Collaboration with the research group of Joe Howard (MPI-CBG).

References

[1] S. Diez, W. R. Schief, J. Howard
Molecular Motors: Single-Molecule Recordings Made Easy.
Current Biology, Vol. 12, R203-205, 2002

[2] C. Leduc, F. Ruhnow, J. Howard, S. Diez
Detection of fractional steps in cargo movement by the collective operation of kinesin-1 motors
Proc Natl Acad Sci USA, Vol. 104, no. 26, pp. 10847-10852, 2007

[3] A. W. Hunter, M. Caplow, D. L. Coy, W. O. Hancock, S. Diez, L. Wordeman, J. Howard
The mechanism of Microtubule Depolymerization by the Kin I Kinesin MCAK: Evidence for the Processivity of a High-affinity ATP-hydrolyzing Complex at Microtubule Ends.
Molecular Cell, Vol. 11, pp. 445-457, 2003

[4] J. Helenius, G. Brouhard, Y. Kalaidzidis, S. Diez, J. Howard
The depolymerizing kinesin MCAK uses 1D-diffusion to rapidly target the ends of microtubules
Nature, Vol. 441, pp. 115-119, 2006

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