DNA origami has grown 10 times
Chemists have increased the size of single-stranded DNA origami by an order of magnitude
Alexander Dubov, N+1
Using the nucleic acid origami technique, chemists assembled the largest structures with a predetermined geometry from single–stranded molecules - in particular, they managed to assemble a rhombus, a heart and a smiley face. As a result of the improved approach, it was possible to obtain DNA structures of 10 thousand nucleotides and RNA structures of 6 thousand nucleotides, scientists report in an article in Science (Han et al., Single-stranded DNA and RNA origami).
Drawings from an article in Science.
The structure of nucleic acids (DNA and RNA) is a chain consisting of nucleotides (adenine, cytosine and guanine – in both acids, as well as thymine, which is found only in DNA molecules, and uracil – only in RNA). Due to the fact that nucleotides are capable of forming complementary bonds with each other (guanine with cytosine, and adenine with thymine or uracil), nucleic acids are able to form double helix structures, as well as carry out replication, transcription and translation processes. Chemists decided to use the nature of complementarity of bonds in DNA and RNA origami techniques in order to make artificial structures of a predetermined shape and with the desired arrangement of functional groups from individual single short sections of nucleic acid molecules, folding polymer chains and fixing these folds with the help of special paperclip molecules.
Usually, nucleic acid origami uses molecular loops of rather short chains, which are then joined together into one common structure of several tens of nanometers in size. The same functional structures that could be completely assembled from single molecules contained only 80 to 660 nucleotides. In one of the experiments, it was possible to fold a chain of 1669 nucleotides into an octagon at once, but four auxiliary, shorter molecules were used for this.
A group of chemists from the USA, Germany, France and China, led by Peng Yin from Harvard University, developed a technique by which large nanometer structures of the desired geometry can be assembled from just one long single-stranded nucleic acid molecule (in their work, scientists examined both DNA and RNA).
A diagram of nodes for fixing the desired structure, in which sections of the chain are exchanged between spiral structures. The simulated scheme of the chain unfolding under the action of an external force is shown below.
The proposed mechanism is based on the possibility of exchange of nucleic acid chains between two spiral structures in which two chains are connected by complementary bonds. The authors of the work used two different exchange mechanisms (parallel and antiparallel), which makes it possible to additionally fasten the structure of the molecule in the right places and rigidly fix the geometry of the entire system. The microstructure of the formed systems of nucleic acids was studied by the authors using an atomic force microscope.
As a result, the authors of the work managed to assemble systems of various pre-defined geometries from single-stranded DNA in 10 thousand nucleotides and single-stranded RNA in 6 thousand nucleotides. The geometry of the obtained nanostructures ranging in size from 10 to 30 nanometers was changed by the authors of the work in a fairly wide range: these could be triangles, parallelograms, circles and heart-shaped figures.
The structure of the "DNA smiley" from a single-stranded molecule (left), and micrographs of experimentally obtained structures made using atomic force microscopy.
In addition, in their work, chemists have shown the ability to attach functional groups to nucleic acid molecules in the right places. With this approach, for example, round DNA structures were turned into emoticons.
Scientists note that the systems that can be obtained using the DNA and RNA origami technique are already much closer to real applications. The authors hope that the proposed technique, due to the possibility of reproduction in biological conditions, will help to obtain single-stranded structures that can be used, for example, for nanomedicine.
Last week, some of the scientists who were part of the team of authors of this work, together with colleagues from Germany and France, published an article in which they proposed a reverse approach to DNA origami - using very short DNA molecules consisting of only a few dozen nucleotides. Systems of two or three such molecules are "bricks", from which, as from the parts of the designer, it is possible to assemble large and complex three-dimensional structures.
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