Molecular Motors

Energy Transformation in
Biological Molecular Motors
Alexander Vologodskii
What is the molecule mechanism of
transforming the energy of ATP hydrolysis
into directed motion?
1. Macroscopic example of a motor action
2. Motion without inertia
3. Allosteric transitions and rectified diffusion
4. Kinetic consideration
5. Experimental data
Contraction of the skeletal muscle
The skeletal muscle cell
Contraction of the skeletal muscle
Myofibrils consist of myosin and actin filaments
Contraction of the skeletal muscle
Myosin filament
Displacement of the myosin head
The major fuel in molecular motors is ATP
How a molecular motor could transform the
energy of ATP hydrolysis into directed motion?
Considering this question we have to take into account
that there is no inertia in this scale in a liquid
Let us consider motion of a bead in water
There are two major ideas in the theory of
molecular motors
The first idea is a key role of rectified thermal diffusion
The idea in this context was pioneered by Huxley in 1957
The second idea is the allosteric transitions in proteins
Before binding the ligand
A
x1
B
x2
x
x2
x
After binding the ligand
x1
Example of the allosteric transition in protein
Mowbray SL, Cole LB. 1.7 A X-ray structure of the periplasmic ribose receptor from Escherichia coli.
J Mol Biol 1992;225:155–75.
Bjorkman AJ, Mowbray SL. Multiple open forms of ribose-binding protein trace the path of its
conformational change. J Mol Biol 1998;279:651–64.
Changing of the free energy potential on ribose binding
Ravindranathan KP, Gallicchio E, Levy RM. Conformational equilibria and free energy profiles for the
allosteric transition of the ribosebinding protein. J Mol Biol 2005;353:196–210.
Explain how the two ideas create
the theory of energy transformation
Diagram of the myosin head cycle
Can diffusion provide the needed speed of
the muscle contraction?
A single cycle of a myosin head takes 0.1 – 30 ms.
The rate of allosteric transitions in proteins is about 104 s-1
Is there experimental data supporting this theory?
τ = τ0exp(-Fd/kT)
It is possible to measure how the rate
depends on the drugging force
Thank you for attention
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