Cell-based nano machine breaks record
CAMBRIDGE, Mass. (December 12, 2005) — Researchers
have known for some time that a long, fibrous coil grown
by a single-cell protozoan is, gram for gram, more powerful
than a car engine. Now, researchers at Whitehead Institute—together
with colleagues at MIT, Marine Biological Laboratory
in Woods Hole, MA, and University of Illinois, Chicago—have
found that this coil is far stronger than previously
thought. In addition, the researchers have discovered
clues into the mechanism behind this microscopic powerhouse.
"These findings are twofold," says Danielle
France, a graduate student in the lab of Whitehead Member
Paul
Matsudaira, and, along with Matsudaira, a member
of MIT's Division of Biological Engineering. "First,
they give us an idea of how a cell can manage to generate
such enormous force; and second, they provide clues
for how engineers might reconstruct these mechanisms
for nano-scale devices."
France will present her findings Sunday, December 11,
at the 45th Annual Meeting of the American Society for
Cell Biology in San Francisco.
Scientists have known about this nano-spring for roughly
300 years, ever since Anton van Leeuwenhoek first observed
the protozoan, Vorticella convallaria, through
a hand-made microscope. The spring in the unicellular
Vorticella is a contractile fiber bundle, called
the spasmoneme, which runs the length of the stalk.
At rest, the stalk is elongated like a stretched telephone
cord. When it contracts, the spasmoneme winds back in
a flash, forming a tight coil. To find out how strongly
Vorticella recoils, France and colleagues used
a unique microscope to apply an extra load to the spring.
The microscope, developed by Shinya Inoue and colleagues
at the Marine Biological Laboratory in Woods Hole, MA,
uses a spinning platform to increase the centrifugal
force exerted against the protozoan.
In the past, researchers have measured Vorticella's
ability to recoil its spring at 40 nano newtons of force
and at a speed of eight centimeters per second, units
of measurement that are typically too large to be relevant
for biological processes. (These measurements, when
scaled up to the size of a car engine, prove the Vorticella
to be the more powerful of the two.) However, when France
used the centrifuge microscope, she discovered that
the spring was able to recoil against as much as 300
nano newtons of force.
"This is the maximum amount of power we can currently
test," says France. "We suspect the coil is
even more powerful."
France and colleagues also made an important link between
the engine's fuel, calcium, and a major protein component
of the stalk. This protein, centrin, belongs to a class
of proteins that can be found in organisms ranging from
green algae to humans. When the researchers introduced
an antibody for the Vorticella centrin into
the cell, the spring was no longer able to contract,
indicating that the cell uses a powerful centrin-based
mechanism, one that is unlike other known cellular engines.
"When it comes to creating nano devices, this is
a great mechanism for movement," says France. "Rather
than requiring electricity, this is a way to generate
movement simply from a change in the chemical environment.
Here, a simple change in calcium would power this spring."
France and colleagues are now developing methods for
replicating this mechanism in the lab.
This research was funded by the U.S. Army.
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