While searching for genes involved in how bacteria stop moving around and settle into stationary communities called biofilms, scientists discovered a molecular clutch that disengages the powerful molecular motor that spins the flagellum that propels the bacteria. This flagellum clutch mechanism may provide ideas useful for nanotech control of molecular motors. From Indiana University, via AAAS EurekAlert “Microscopic ‘clutch’ puts flagellum in neutral“:
A tiny but powerful engine that propels the bacterium Bacillus subtilis through liquids is disengaged from the corkscrew-like flagellum by a protein clutch, Indiana University Bloomington and Harvard University scientists have learned. Their report appears in this week’s Science [abstract].
Scientists have long known what drives the flagellum to spin, but what causes the flagellum to stop spinning — temporarily or permanently — was unknown.
“We think it’s pretty cool that evolving bacteria and human engineers arrived at a similar solution to the same problem,” said IU Bloomington biologist Daniel Kearns, who led the project. “How do you temporarily stop a motor once it gets going?”
The action of the protein they discovered, EpsE, is very similar to that of a car clutch. In cars, the clutch controls whether a car’s engine is connected to the parts that spin its wheels. With the engine and gears disengaged from each other, the car may continue to move, but only because of its prior momentum; the wheels are no longer powered.
EpsE is thought to “sit down,” as Kearns describes it, on the flagellum’s rotor, a donut-shaped structure at the base of the flagellum. EpsE’s interaction with a rotor protein called FliG causes a shape change in the rotor that disengages it from the flagellum’s proton-powered engine.
…The discovery may give nanotechnologists ideas about how to regulate tiny engines of their own creation. The flagellum is one of nature’s smallest and most powerful motors — ones like those produced by B. subtilis can rotate more than 200 times per second, driven by 1,400 piconewton-nanometers of torque. That’s quite a bit of (miniature) horsepower for a machine whose width stretches only a few dozen nanometers.