Inside nature’s most efficient motor: the flagellar

It’s one of nature’s most impressive machines, yet it’s barely nanometres wide. It’s a motor with 99 per cent efficiency that can rotate at up to 100,000 rpm, and switch directions faster than any device created by human ingenuity.

It’s the bacterial flagellar (also known as the flagella or flagellum), and a team of Australian scientists from The Victor Chang Cardiac Research Institute (VCCRI) has revealed for the first time the details of the protein structures that make it tick, and spin.

“From a technological point of view, the flagellar is fascinating,” said Lawrence Lee, one of the authors of the paper. “It goes above and beyond anything man has done. But the way nature does this involved process was poorly understood.” Until now.

The paper, which appeared in Nature today, is the culmination of years of work in the lab at the VCCRI.

The team outline how they used X-ray crystallography to build a precise 3-D image of the positions of a key protein, FliG, which forms a ring in the rotor of the flagellar, and is involved in producing its impressive rotational torque.

They also uncovered how the flagellar is able to perform an astounding trick: switching the direction of rotation almost instantaneously.

The team found that the protein, FliG, can change its position within the ring, and when it does it reverses the rotation of the flagellar.

This manoeuvre is essential for bacteria to change direction, where they change the rotation of some or all of their flagellar, causing them to tumble to a new orientation, then synchronise their rotation again to drive forward in the new direction.

This intimate knowledge of the flagellar could lead to new targets for anti-bacterial drugs that can, quite literally, stop bacteria in their tracks.

If a drug can be found that precisely targets and disrupts one of the proteins in the flagellar, it could leave bacteria unable to move.

“What we have here is a precise molecular structure,” said Lee. “From this we can infer where something specifically binds. So this finding gives a framework to begin developing drugs that target the flagellar motor.”

“This work really unifies the results of decades of international scientific study, and is a coup for Australian science,” said Professor Bob Graham, Executive Director at the VCCRI.

“The fact we can now understand how these bacteria generate movement and change direction is of critical importance, not only for biologists around the world, but for the future design of nano-machines as well.”

The paper was published in Nature: doi:10.1038/nature09300.

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