What is DNA origami?

DNA nanostructures in which a single long strand of DNA is folded so that it runs through every double helix. The term is by analogy with the Japanese art of paper folding in which a single sheet of paper is folded, without cuts, to create elaborate three-dimensional shapes. Conceptually, there are two types of DNA origami. In single stranded DNA origami, the structure is formed entirely by a single long strand and the folding is due to interactions of the long strand with itself. In scaffolded DNA origami, the folds are formed by the interaction of a long single strand and hundreds of short DNA strands called “staples”. Single-stranded origami structures have the advantage of being clonable, potentially exponentially reproducible like living things. So far, an almost-single-stranded DNA octahedron with just five staples has been reported. Scaffolded DNA origami structures have been easier to design and synthesize; a half dozen two-dimensional shapes including a star, rectangle, triangle and smiley face, as well as a threedimensional hexagonal tube have been reported. Scaffolded DNA origami structures are easily connected to other nanoscale objects such as carbon nanotubes and proteins, and might be used to organize them into complex nanocircuits or nanofactories.

How the DNA nanoarchitecturing works?

DNA nanoarchitectures constructs that can be self-assembled from branched DNA molecules. Their components may be simple branched species or more complex structural motifs. Simple branched DNA junctions have been produced that contain 3–12 double helices flanking a branch point. The species can be assembled and/ or ligated into DNA stick polyhedra, where the edges are DNA double helices and the vertices correspond to the branch points of the junctions. The first such molecule was a DNA molecule with the connectivity of a cube. Other polyhedra produced to date include a tetrahedron, an octahedron and a truncated octahedron. Branched junctions are somewhat floppy, so only the branching and linking topologies of polyhedral are well defined unless all the faces are triangles. Other individual objects that have been built are topological targets, such as knots and Borromean rings. DNA is an ideal species to use as a topological building block because a half-turn of DNA is equivalent to a node, which is the fundamental topological feature of a knot or a catenane. The DNA double-crossover (DX) molecule is another key element in DNA nanoarchitectures. This motif consists of two helices joined twice by strands that connect them, leading to parallel helix axes; the connection points are separated typically by Two-dimensional DNA lattice. one and two double helical turns. Each of the connection points is a four-arm junction, so the motif can be described as two four-arm junctions joined twice to each other at adjacent arms. These are robust motifs, usually three to six double helical turns in length and their structures can be reliably predicted. This system can be extended, leading to molecules containing three or more helices joined laterally. Although most often built to be roughly planar motifs, angles can be varied between pairs of helices, using the helicity of DNA, e.g. a six-helix cyclic motif has been reported that approximates a hexagonal tube (→DNA nanotubes). DX molecules and their relatives can be exploited as tiles to produce two-dimensional crystalline arrangements by self-assembly (→DNA self-assembly). An extra motif can be included in these tiles, visible when the crystal is viewed in an atomic force microscope. The accompanying picture shows how arrangements of two 16 × 4 nm tiles produce 32-nm stripes (top) or four tiles produce 64-nm stripes (bottom). In addition to periodic arrangements, aperiodic patterns can also be generated algorithmically. Single-stranded bacteriophages have been used to produce greatly extended versions of the parallel DNA motif, capable of yielding highly elaborate patterns, in a method called DNA origami. This is done by using the bacteriophage genome (several thousand nucleotides) as a template to which a large number of “staple strands” are added to fold the genome into a specific shape, including holes in the middle; the addition of strands containing extra domains enable the generation of further features. Smiley faces and a map of the western hemisphere are examples of patterns generated by this method.