Viewing molecular motor motion: The FoF1 synthase is oriented so that the F1 component attached via histidine linkages to a nickel-coated microscope slide (gray rectangle). A gold nanorod is bound by avidin-biotin to the c-subunit ring of the Fo complex (represented by light and dark gray bands), which rotate relative to subunit-a (bright green dowels). An axel (dark green) connects the FoF1 motors. The stabilizing nanodisc is portrayed with blue segments and brown lipid bilayer dumbells.
by a $1.2 million grant from the National Institutes of Health (NIH),
Arizona State University scientist Wayne Frasch is deciphering how one
of the world’s smallest molecular motors works in living cells. In the
process, he is also casting light on a physics puzzle that has perplexed
scientists for more than 40 years.
a professor in the School of Life Sciences, examines the Fo molecular
motor, its mechanism of action and how it partners with the F1 motor as
part of the FoF1 ATP synthase. At about 10 nanometers in diameter, each
motor is 10,000 times smaller than the width of a piece of paper. In
living things, Fo and F1 are attached by a common rotary axel that
allows the two motors to work together and supply energy to cells in the
form of adenosine triphosphate (ATP).
of nanoscale motors is not just complicated by size. Molecular motors
operate via extremely small motions that occur on time scales that have
been extraordinarily difficult to measure. The Fo molecular motor is
also embedded in a living cell’s lipid membrane, which is only two
molecules thick. Adding to the experimental challenge is the fact that
the molecular motors’ rotational energy arises from the flow of protons,
positively-charged atomic particles, across that membrane.
Frasch lab is among only a few laboratories equipped to visualize how a
single molecule of the Fo motor rotates. Frasch and his ASU College of
Liberal Arts and Sciences colleagues have developed an experimental
system that embeds the Fo motor in an artificial phospholipid bilayer
laid down in nanodiscs, which help to stabilize the molecular complexes.
Frasch’s group then devised an imaging strategy, using gold nanorods
attached to Fo to monitor the rotation of the single FoF1 molecules.
more about these tiny, but extraordinarily efficient –nearly 100
percent – molecular motors offers an avenue to development new
technologies, such as power sources for fuel-efficient nanodevices and
nanotechnology applications like molecular detection, computing and
biomedicine,” Frasch says.
One early outcome of Frasch and the ASU team’s FoF1 experiments, recently published in EMBO Journal,
provides enticing new clues into an old conundrum: a Brownian ratchet
first proposed by physicist Richard Feynman more than 40 years ago.
studies of the Fo motor led researchers to propose that Fo contains a
molecular ratchet capable of biasing Brownian motion, the random motion
of molecules, in a way that favors rotation in the direction of ATP
synthesis,” says Frasch. “However, little evidence existed for the type
of periodic interruptions in rotation consistent with this type of
was known is that the flow of protons across the membrane through Fo
channels in a static subunit-“a” drives clockwise rotation of the
“c”-ring rotor comprised of 10 c-subunits that each shuttle a single
proton. This clockwise rotation in turn drives ATP synthesis, which
occurs in the F1 motor because the c-ring attaches to one end of the
axle that links units Fo and F1.
a gold nanorod attached to the c-ring of a single FoF1 molecule,
Frasch’s group can examine the motor’s rotation in more depth. The group
measures changes in light intensity from the gold nanorod as it (and
the c-ring) rotates, which allows the ASU team to “see” that the rotary
motion of the c-ring is periodically interrupted.
subunit-a grabbed onto subunit-c, the interaction behaved as a leash,
allowing the c-ring to rotate, but at a limit of 36 degree increments
while engaged – like a ratchet,” Frasch says, “This periodic
interruption only occurred under conditions in which there was
sufficient drag on the nanorod to slow the motor, similar to conditions
found in a living cell where ATP is maintained at a high level.”
the new NIH funding, Frasch’s School of Life Sciences research group
will examine if the leash is a component of the long sought after
Browning ratchet. Understanding how or if Brownian motion is harnessed
in a molecular ratchet has the potential for use in the development of
synthetic molecular motors with low energy consumption and nanoscale