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Figure 13.19 illustrates the application of three-dimensional DNA lattices to
scaffolding of proteins into regular 3D arrays. It has been estimated that at least
one half of all natural proteins cannot be readily crystallized and have unknown
structure; determining these structures would have a major impact in the
biological sciences. Suppose a 3D DNA lattice can be assembled with sufficient
regularity and with regular interstices (say, within each DNA tile comprising the
lattice). Then a given protein might be captured within each of the lattice's
interstices, allowing it to be in a fixed orientation at each of its regularly spaced
locations in 3D. This would allow the protein to be arranged in 3D in a regular
way to allow for X-ray crystallography studies of its structure. This visionary idea
is due to Seeman. So far there has been only limited success in assembling 3D
DNA lattices, and they do not yet have the degree of regularity (down to 2 or 3A
˚
)
required for the envisioned X-ray crystallography studies. However, given the
successes up to now for 2D DNA lattices, this seems eventually achievable.
13.9. AUTONOMOUS MOLECULAR TRANSPORT DEVICES
SELF-ASSEMBLED FROM DNA
There are a number of other tasks that can be done at the molecular scale that
would be considerably aided by this technology. For example, many molecular-
scale tasks may require the transport of molecules. The cell uses protein motors
fueled by ATP to do this. While a number of motors composed of DNA
nanostructures have been demonstrated, they do not operate autonomously, and
instead require some sort of externally mediated changes (such as temperature-
cycling) on each work-cycle of the motor.
Peng et al. [23] experimentally demonstrated the first autonomously operating
device composed of DNA providing transport as described in Figures 13.20 and 21.
First a linear DNA nanostructure (the ''road'') with a series of attached
ssDNA strands (the ''steps'') was self-assembled, as illustrated in Figure 13.20. A
fixed-length segment of DNA helix (the ''walker'') with short sticky ends (it's
A
∗
B
C
Walker
3
3
Anchorage
13
16
13
13
16
16
Backbone
Hinge
15
21
4
32
31
99
Figure
13.20.
Design of autonomous molecular transport devices self-assembled
from DNA.
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