Living cells are full of tiny molecular machines that perform numerous tasks there: from wiggling the scourge of a bacterium to the production of ATP molecules, the energy girders of a cell. Now biophysicists from the Technical University of Munich have succeeded in building a tiny engine completely made of DNA strands outside of a cell that can briefly store energy by winding up a "spring".
It is not the first DNA nanomotor, but "certainly the first one that actually does measurable, mechanical work," says Hendrik Dietz, physicist and professor of molecular robotics at the Technical University of Munich, whose team has now published the results in "Nature". The technique joins a growing list of DNA origami tricks used to build structures at the molecular level. Dietz envisions that this could one day be used to construct tiny DNA nanofactories that could then be used in chemical synthesis or the targeted administration of drugs.
Munich-based DNA Origami technology further developed
Dietz's research group is a world leader in the development and application of the DNA origami technique. First, single-stranded DNA loops are grown in bacteria and mixed in a solution with short strands of synthetic DNA. The short pieces connect with the long strands, forcing them to fold into the desired shape. If you choose all the components skillfully, the puzzle will assemble in the test tube almost by itself. Since the first demonstration of this technique in 2006 by Paul W. K. Rothemund from the California Institute of Technology, the Munich-based company has further developed the principle and built increasingly complex DNA origami.
The newly designed DNA nanomotors work with ratchet mechanisms, similar to the gears in clockwork, the turns in one direction, but not in the other. Like everything else in the cell, they are constantly confused by the Brown -Movement - the constant, random movement of molecules and other particles in cytoplasm. When particles put together, they give each other an "energy kick".
For the engines, the researchers built triangular platforms made of DNA, from each of which a rod protruded. They glued these structures, about 30 by 40 nanometers, to a glass surface and added long DNA arms attached to the platforms so that they could rotate around the rod.
Brownian motion drives nanomotors
To create a ratchet effect, they provided the platforms with bumps that make this rotation difficult. Only the bumps triggered by the Brown movement enabled the poor to overcome the bumps and turn, usually half a revolution.
The rotation would easily go back and forth. Therefore, the team dipped two electrodes in the solution and let an electrical alternating current flow. The changing direction of the tension changed the energy landscape, which was exposed to the long DNA arms, and made it cheaper to turn in a direction through a mechanism that is known as a flashing Brown Ratchet.
Very happy to share our first molecular motor made of DNA, open access to everyone to read @Nature . It is a ratchet! And it can wind a spindle. pic.twitter.com/OWywbjV1mn
This made the passive devices into real engines. Microscopic recordings show that under these conditions every arm - although he accidentally shook himself - always turned in the same direction on average.
By itself, the nanomotor does nothing more than overcome the resistance of the surrounding solution. "It's like swimming: you move forward and do a lot of work that evaporates in the water," says Dietz. But to show that the motor can also do potentially useful work, the researchers went one step further: They attached another strand of DNA to their rotor and had it rolled up like the hairspring used to turn the gears in a mechanical watch. Such a mechanism could help nanomachines store energy or pull on other mechanical components, Dietz says.
For him, the engine is an important first proof that the principle works and that not only static nanosystems can be produced with the help of the DNA origami technique, but also those that can do work. "Of course, I was very pleased about the publication of our work in Nature," says Hendrik Dietz. "But for me it is above all an incentive to think directly about the next project." After all, his chair has just been renamed from "Molecular Design" to "Molecular Robotics".
