"Design"

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 Background

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Biomolecular motor system such as microtubule-kinesin is an example of smallest natural machine
that can convert chemical energy obtained from ATP into mechanical work with high efficiency and
specific power. Nowadays microtubule-kinesin system, one of the biomolecular motor system, is being
used as a building block for constructing micro-actuators and driving unit of the biodevices. Kinesin
converts chemical energy derived from the hydrolysis of ATP molecules into directed, stepwise motion
along microtubule.

Our experimental system is the assembly of biotinylated microtubules cross-linked
through the interaction of streptavidin via active transport on a kinesin-coated surface.This process
is called dynamic self-organization and has been drawing much attention to integrate highly organized
microtubule assemblies.
Ring-shaped microtubule assemblies have been demonstrated to obtain through dynamic self-organization.
Considering the advantage of its geometry and handedness, they have appeared to be a promising tool
to harness continuous rotational motion without changing the position of its mass center.

 Problem

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Although ring-shaped microtubules possess immense potential with respect to their prospective
application in nanotechnology, several barriers needed to be surmounted yet as listed below.

No.1

          
In a closed system, consumption of energy spoils the potential activity of ring-shaped
microtubules. Supply of energy through ATP hydrolysis is a prerequisite to keep the ring-shaped
microtubules working continuously. Development of a system to provide energy continuously is
highly desired.

No.2

               
It is still unknown how much power we can harness from the rotational motion of the ring-shaped
microtubules. Once known, the power could be designed to use further in an appropriate way.

No.3

               
No system has been developed yet that can work by transmitting the power harnessed from
ring-shaped microtubules. This drawback is preventing integration or amplification of the power
of smallest natural machines.

 Solution

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Solution for the problem 1

Ring-shaped microtubules are driven by kinesin where the energy comes from the hydrolysis
of ATP to ADP. A system that can use the ADP to reproduce ATP allow us to keep the ring-shaped
microtubules working continuously. To develop such a system, we synthesize micro gels
which contain F1/F0- ATPase together with photosystems. This gel is termed as “Marimo-Gel”.
The Marimo-Gel converts ADP to ATP by utilizing the energy from light.

Solution for the problem 2

Optical tweezers are powerful tool to measure force as small as pico- to nano- newton (N). Use of
optical tweezers allows us to know the force generated from the rotational motion of ring-shaped
microtubules. To detect the force we attach a polystyrene bead (～5 µm) to the top surface of the
ring-shaped microtubule via biotin-streptavidin interaction. After capturing the bead by optical tweezers
we determine the force of the ring-shaped microtubules from the displacement of the bead during
the rotational motion.

Solution for the problem 3

    

To harness the power of rotating ring-shaped microtubules we prepare micrometer-sized synthetic gear.
With the help of optical tweezers the synthetic gear is placed on the ring-shaped microtubule assemblies.
For fixing the gear firmly with the rings a specific streptavidin-biotin interaction could be used. By
arranging ring-shaped microtubules and gears properly we can amplify the power which then can be used for
doing further work.

Advance
Solution 1+Solution 2+Solution 3

Solutions discussed above collectively will have a big impact in making practical use of motor protein
based biodevices.