Stickiness is needed to keep the molecules in a certain place – otherwise thermal energy would blow them away just like a hurricane does in the macroscopic world.
Dr Mathias Strackharn
Researchers at Ludwigs-Maximilians-Universität
(LMU) in Munich have developed an approach which allows them to pick up and move individual molecules in order to construct biomolecular machines with nanometre precision.
The Single-Molecule Cut and Paste (SMC&P) technique was devised in its original form by Professor Hermann Gaub’s research group, based at LMU, but this approach was compatible only for use with DNA molecules. The method has been modified by a new team for use with proteins, which are responsible for many of the most important cellular processes.
Dr Mathias Strackharn, first author of the study which was published in the Journal of the American Chemical Society
at the beginning of this month, spoke to ScienceOmega.com
about the challenges presented by working on such a small scale and the potential applications of the new tool. He began by detailing some of the background of research in the field.
"The arrangement of single molecules to form complexes with new properties is one of the main goals of nanotechnology. Already in the 1990s Don Eigler and colleagues could arrange single atoms to form new complexes, but these experiments were conducted at 4 K (ie at -270 °C) and in ultra-high vacuum."
Of course, as Dr Strackharn pointed out, it is by no means possible for biological matter to function under these conditions; to do so it requires conditions akin to our everyday weather.
"In SMC&P we have developed for the first time a method which is capable of arranging biomolecules with nanometre precision," stated Dr Strackharn. "In the proof of principle experiments we basically combined the stickiness of DNA molecules with the precision of an atomic force microscope (AFM), which acts like the manipulator's finger. Stickiness is needed to keep the molecules in a certain place – otherwise thermal energy would blow them away just like a hurricane does in the macroscopic world."
The molecules are first stored in a ‘depot’ before being taken by the finely-honed tip of the AFM cantilever which grips them more firmly. Finally they are deposited at the construction site, where they are held with the highest force. The major challenge for the nanoscale arrangement of proteins via the SMC&P technique was to create a hierarchical force system to meet the requirements of the proteins being manipulated.
"The forces acting on our protein of interest have to be fine-tuned and must not be so large that they destroy the protein’s functionality," Dr Strackharn stated. "We made use of the highly specialised binding properties of antibodies, ‘zinc finger’ molecules and DNA to solve that problem. The interplay of all these molecules allows us to transfer single proteins with the precision of an AFM."
To demonstrate the practical application of the method, the scientists arranged hundreds of green fluorescent proteins (GFPs) in the form of the familiar green man from pedestrian crossings, but just micrometres tall.
"The assembly of micron-sized traffic signals proved not only that the transfer mechanism worked over and over again, but also that the very sensitive proteins could take up their work again – in our case creating fluorescent light," Dr Strackharn explained.
Potentially, the technique can be used to examine in detail the com-plex relationships between various proteins and the biomolecular machines they make up. Dr Strackharn also emphasised the possibility that sustainability could be improved with the creation of organic biomass-to-biofuel converters.
"Nature very often uses interacting proteins, but exactly how these proteins play together – how their coupling influences their work – needs to be further illuminated," he said. "We have now created a tool for the artificial construction of these interacting protein combinations. For example, it allows us to test how different spacings between our molecular machines influence the output.
"Another very interesting system that we now focus on is the cellulosome, a well-ordered set of proteins that breaks down plant sugars. We hope that we can help to understand the details of the working mechanism and also to show how one can construct improved breakdown machinery, which would be highly desirable for the energetic use of waste cellulose, for example."