Scientists successfully finish tiny DNA 'unicycle's test drive

Nanomachines include structures of complex proteins and nucleic acids. The principle is inspired from nature. Bacteria, for example, propel themselves forward using a flagellum.

Researchers from the University of Bonn in Germany and the University of Michigan in the US used structures made of DNA nanorings. The two rings are linked like a chain.

"One ring fulfills the function of a wheel, the other drives it like an engine with the help of chemical energy," said Michael Famulok from the Life and Medical Sciences (LIMES) Institute of the University of Bonn.

The tiny vehicle measures only about 30 nanometers. The "fuel" is provided by the protein "T7 RNA polymerase", according to the study published in the journal Nature Nanotechnology.

Coupled to the ring that serves as an engine, this enzyme synthesises an RNA strand based on the DNA sequence and uses the chemical energy released during this process for the rotational movement of the DNA ring.

"As the rotation progresses, the RNA strand grows like a thread from the RNA polymerase," said Julian Valero from University of Bonn.

The researchers are using this ever-expanding RNA thread, which basically protrudes from the engine as a waste product, to keep the tiny vehicle on its course by using markings on a DNA-nanotube track.

Attached to this thread, the unicycle machine covered about 240 nanometers on its test drive.

In the next step the researchers are not only aiming at expanding the length of the route, but also plan more complex challenges on the test track. At built-in junctions, the nanomachine should decide which way to go.

"We can use our methods to predetermine which turn the machine should take," said Valero with a view towards the future.

By using an atomic force microscope that scanned the surface structure of the nanomachine, the scientists were able to visualise the interlocked DNA rings.

The team also used fluorescent markers to show that the "wheel" of the machine was actually turning. Fluorescent "waymarkers" along the nanotube path lit up as soon as the nano-unicycle passed them.

Unlike macroscopic machines, the nanomachine was not assembled with a welding torch or wrench. The construction is based on the principle of self-organisation.

As in living cells, the desired structures arise spontaneously when the corresponding components are made available.

"It works like an imaginary puzzle," said Famulok.

Each puzzle piece is designed to interact with very specific partners. If you bring together exactly these partners in a single vessel, each particle will find its partner and the desired structure is automatically created, he said.