Dream Machines from Beans: Legume proteins provide motion

Cells, tiny as they are, are packed with molecular machinery that investigators can exploit for their own purposes. German scientists now report that certain protein complexes in fava beans have characteristics that might make the complexes useful as valves in microfluidic devices.

CELL STOPPER. A forisome (red) at rest in a bean plant’s fluid-moving sieve tube. A jolt of calcium would make the forisome expand and seal off the 1-cell-wide tube. Knoblauch and Peters

“It’s always difficult to find actuators, or moving parts, that can be controlled neatly and will do what you want them to do on a small scale,” says Winfried S. Peters, a biologist at Justus Liebig University in Giessen, Germany. He, Michael Knoblauch, and their colleagues report in the September Nature Materials that they’ve identified just such an actuator. In the beans, the needle-shaped protein complexes are situated in so-called sieve tubes, where they control the plant’s flow of sugar-bearing fluid.

When exposed to calcium, these long, thin structures, dubbed forisomes, shorten by about one-third of their original lengths of 18 to 34 micrometers, the researchers find. At the same time, the complexes fatten to more than twice their original girths.

When the researchers remove the calcium, the forisomes revert to their previous shape. The complexes also show mechanical responses to pH changes and electrical stimulation.

Perhaps equally important for practical purposes is that these bean-derived actuators work without adenosine triphosphate (ATP), comments Constantinos Mavroidis of Rutgers University in Piscataway, N.J. ATP is the standard biochemical fuel that cells use to run most of their machinery (SN: 11/9/02, p. 291: Available to subscribers at Nanotech Switch: Strategy controls minuscule motor).

“The dependence on ATP means there is a dependence on a special chemical environment” for many actuators from nature, says Mavroidis. Calcium can be used under simpler conditions, he notes.

That simplicity could serve well in systems where forisomes would open or seal off tiny pipelines to control the movement of minute amounts of reagents or would act as microforceps, says Peters. He and his colleagues have already demonstrated that forisomes can control the microscopic spacing between the tips of two glass pipettes.

With further work, forisomes could become the basis of pistons in minimotors, suggests Mavroidis. A thousand times as large as nanoscale components, forisomes would be easier to see and control. “It gives an enormous amount of possibilities for inventions and devices,” says Mavroidis.

The German team is currently investigating how forisomes shift shapes and searching for still smaller units of the protein that could work as actuators in even more miniaturized mechanical devices.

“The more we understand how living systems work,” says Carlo Montemagno of the University of California, Los Angeles, “the more we’re going to find that they are designed and structured in ways that we would like to use to fabricate and engineer nanomachines.”


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