Two rings of DNA only 18 nm in size have been interlocked like two links in a chain. Such a structure is called catenan, a term derived from the Latin word catena (chain). |
Creating
artificial structures from DNA is the objective of DNA nanotechnology.
This new discipline, which combines biology, physics, chemistry and
material science makes use of the ability of the natural DNA-strains’
capacity for self assembly. Smileys or small boxes, measuring only 10s
of nanometers (10 one-billionths of a meter) were created from DNA in a
drop of water.
Prof
Alexander Heckel and his doctoral student Thorsten Schmidt from the
“Cluster of Excellence for Macromolecular Complexes” at Goethe
University were able to create two rings of DNA only 18 nanometers in
size, and to interlock them like two links in a chain. Such a structure
is called catenan, a term derived from the Latin word catena (chain).
Schmidt, who got married during the time he was working on the
nano-rings, believes that they are probably the world’s smallest wedding
rings.
From
a scientific perspective, the structure is a milestone in the field of
DNA nanotechnology, since the two rings of the catenan are, as opposed
to the majority of the DNA nanoarchitechtures that have already been
realized, not fixed formations, but – depending on the environmental
conditions—freely pivotable. They are therefore suitable as components
of molecular machines or of a molecular motor. “We still have a long way
to go before DNA structures such as the catenan can be used in everyday
items,” says Prof Alexander Heckel, “but structures of DNA can, in the
near future, be used to arrange and study proteins or other molecules
that are too small for a direct manipulation, by means of
auto-organization.”
This way, DNA nano-architectures could become a versatile tool for the nanometer world, to which access is difficult.
In
the manufacture of DNA nano-architecture, the scientists take advantage
of the pairing rules of the four DNA nucleobases, according to which
two natural DNA strands can also find each other (in DNA
nano-architecture, the base order is without biological significance).
An A on one strand pairs with T on the other strand and C is
complementary to G. The trick is to create the sequences of the DNA
strands involved in such a manner as to ensure that the desired
structure builds up on its own without direct intervention on the
experimenter’s part. If only certain parts of the strands used
complement each other, branches and junctions can be created.
As
reported by Schmidt and Heckel in the journal Nano Letters, they first
created two C-shaped DNA-fragments for the catenans. With the help of
special molecules that act as sequence-specific glue for the double
helix, they arranged the “Cs” in such a ways as to create two junctions,
with the open ends of the “Cs” pointing away from each other (see
images). The catenan was created by adding two strands that attach to
the ends of the two ring fragments, which are still open. Thorsten
Schmidt dedicated the publication to his wife Dr Diana Gonçalves
Schmidt, who also appreciates the work on scientific level, since she
was also a part of Alexander Heckel’s work group.
Since
they are much smaller than the wavelengths of visible light, the rings
cannot be seen with a standard microscope. “You would have to string
together about 4000 such rings to even achieve the diameter of a human
hair”, says Thorsten Schmidt. He therefore displays the catenans with a
scanning force microscope, which scans the rings that have been placed
on a surface with an extremely fine tip.
Construction of a Structurally Defined Double-Stranded DNA Catenane
