Directed binding |
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Authors: | H Bolterauer J A Tuszynski E Unger |
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Institution: | (1) Institute of Theoretical Physics, Justus Liebig Universitaet Giessen, D-35392 Giessen, Germany;(2) Department of Physics, University of Alberta, T6G 2J1 Edmonton, Alberta, Canada;(3) Department of single Cell and Single Molecule Techniques, Institute of Molecular Biotechnology, 17745 Beutenbergstrasse 11, Jena, Germany |
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Abstract: | We propose a novel physical mechanism to describe the mode of processive propagation of twoheaded kinesin motor proteins along
microtubule (MT) filaments. Binding and unbinding of the kinesin heads to and from the MT filament play a crucial role in
producing movement. The chemical energy of adenosine triphosphate hydrolysis is used in large part for the unbinding process
of kinesin from the MT filament. Importantly, in our model, the binding of each head is to be directionally oriented to the
MT filament. Therefore, we treat the two motor domains (heads) as extended objects that are connected with each other by a
neck region that contains the kinesin dimerization domain. The head domains recognize tubulin binding sites by feeling the
two-dimensional periodic potential from the MT surface and are also subjected to thermal noise. Using experimentally determined
results regarding physical parameters of the walk, we develop a simple mathematical and mechanical model in which directed
binding of the heads to tubulin results in a directed twist of the molecule, probably in the neck linker region, away from
its relaxed state. Unbinding of the head from the filament relaxes the twist and defines the propagation direction. We showed
that there must be at least two torsional springs (one for every head) involved that can store elastic energy. Consequently,
in our model, it is the internal structure both of the relaxed and tensed-up state and the transition mode between them that
define the walking direction of kinesin. We present calculations based on the model that are in good quantitative agreement
with experimental observations for kinesin. |
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Keywords: | Kinesin Ncd motor protein Fokker-Planck equation reaction kinetics Langevin equation |
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