Sweating the small stuff Home

Switch Turns Microscopic Motor On And Off
By Philip Ball

Scientists have redesigned one of nature's molecular machines to make the world's smallest switchable motor. The rotating machine can be turned on and off like a pocket fan - but it is only about 14 millionths of a millimetre across1.

The invention brings mechanical devices made from single molecules a step closer. Such machines might form part of electronic circuits, carry out delicate surgery on cells or gather solar energy.

Chemists have had difficulty building molecular motors from scratch. So instead, many researchers are looking to borrow items from the toolkit in living cells, such as the proteins that shunt molecules or cell compartments around.

Two years ago, Carlo Montemagno's group, based at the University of California, Los Angeles, harnessed a motor protein called ATP synthase to drive a microscopic propeller. This protein has a wheel-like rotating head that sits on a spindle embedded in the cell's membrane. As the head rotates, the enzyme converts a molecule called ADP into another called ATP, the cell's main fuel.

The researchers attached ATP synthase molecules to a metal surface, so that the head stayed fixed and its spindle rotated. They then fixed a nickel rod to the spindle so that it spun like a propeller when the protein was fuelled with ATP. Now Montemagno's team has found a way to stop and start this motor.

The researchers added a small chemical group to the protein that seizes zinc ions from solution. When the protein takes up zinc it changes shape and stops the spindle from rotating.

The 'on' switch comes in the form of small molecules that are even more keen on zinc. These strip the metal from the ATP synthase and set it spinning again.

The zinc-loving molecules are tethered to small plastic beads. Adding zinc and then zinc-binding molecules in sequence turns the ATP synthase motor off and then on again.

References

# Liu, H. et al. Control of a biomolecular motor-powered nanodevice with an engineered chemical switch. Nature Materials, Advanced Online Publication doi:10.1038/nmat761, (2002). |Article|

Nature News Service / Macmillan Magazines Ltd 2002