Nanomonocycle
The molecular motor of two DNA rings was taught to move along a given route
Alexander Dubov, N+1
Chemists have synthesized a molecular nanomotor consisting of two DNA rings and an enzyme attached to them. During the operation of the nanomotor, one of the DNA rings rotates, as well as the synthesis of an RNA molecule that remains attached to the enzyme. Using the interaction of the synthesized RNA chain with the substrate, the nanomotor can be directed along a predetermined route, scientists write in Nature Nanotechnology (Valero et al., A bio-hybrid DNA rotor–stator nanoengine that moves along predetermined tracks).
Molecules with a catenane structure are two circular molecular fragments mechanically connected in a chain. No chemical bond is formed between the two elements of the molecule and they are connected only topologically. It is known that molecules with a similar chain structure can be formed as a hydrocarbon skeleton with aromatic and heterocyclic groups, and, for example, DNA molecules. Due to the possibility of free rotation of the rings in such a structure, catenans and related rotaxanes are often used as elements of molecular machines. For example, it is thanks to such molecules that molecular turnstiles and some types of molecular pumps work.
A group of German and American chemists led by Michael Famulok from the University of Bonn has synthesized a biohybrid molecular motor with a catenan structure, which consists of two circular DNA chains and is able to move along a predetermined route. Each of the rings in the synthesized catenane has its own function: a large ring consisting of 210 pairs of nucleotides serves as a rotating "wheel", and a small ring of 168 pairs of nucleotides is a kind of motor for this wheel. The rotation of the wheel is carried out by an enzyme attached simultaneously to both DNA chains – RNA polymerase, whose work is carried out by hydrolysis of nucleoside triphosates (for example, ATP). The size of the entire system is about 30 nanometers.
Schematic representation of the nanomotor structure
(from an article in Nature Nanotechnology).
As guides for the movement of the motor, the authors of the study proposed using DNA nanotubes, to which small single-stranded oligonucleotides are attached at a certain interval. Initially, the stationary ring of the molecular motor is fixed in one of the positions on the nanotube, after which the rotation of the rotary part of the motor is started and the RNA molecule synthesized at the same time, due to attachment to the chains sticking out, causes the motor to "jump" along the nanotube. With the help of such a movement, scientists managed to move the nanomotor along the nanotube at a distance of several hundred nanometers.
Scientists note that the architecture they proposed is quite simple and its configuration can be changed depending on the goals. Thus, it is possible to obtain complex biohybrid molecular machines consisting of a large number of elements working due to the hydrolysis of nucleoside triphosphates.
Catenans are not the only example of complex molecular structures with topological coupling, which is provided not by chemical interaction between atoms, but mechanically – due to the "entanglement" of the molecular structure. For example, last year British chemists synthesized a record-breaking complex molecule-a node with eight intersections of a molecular chain in its structure with a total length of 192 atoms.
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