412 9.3  Synthetic Biology, Biomimicry, and Bionanotechnology

are those of standard molecular cloning (Chapter 7). Similarly, genetic modifications can

include encoding tags next to genes at the level of the DNA sequence, for example, fluor­

escent proteins.

Modified proteins have been used in genuine bottom-​up synthetic assays to build

devices that utilize protein pattern formation. For example, the bacterial proteins MinC,

MinD, and MinE, which are responsible for correctly determining the position of cell

division in growing E. coli bacterial cells (see Chapter 8), have been reconstituted in an

artificial noncellular system involving just microwells of different sizes and shapes. These

systems require an energy input, provided by the hydrolysis of ATP, but then result in fas­

cinating pattern formation depending on the size and shape of the microwell boundaries,

even in the complete absence of cells. These systems have yet to be exploited for “useful”

ends, but show enormous potential at being able to develop controllable patterns in solu­

tion from just a few protein components, which could have implications for templating of

more complexing synthetic devices.

Similarly, other bacterial cell division proteins such as FtsZ have been artificially

reconstituted. FtsZ is responsible for the actual constriction of the cell body during the pro­

cess of cell division, through the formation of a tightening Z-​ring. FtsZ can be reconstituted

and fluorescently labeled in artificial liposomes with no cells present and fueled by GTP

hydrolysis in this case, which can result in controlled liposome constriction that can be

monitored in real time using fluorescence microscopy imaging.

The degron system is also a good example of genetic and protein-​based bioengineering.

As discussed previously (see Chapter 7), this uses genetic modification to insert degron tags

onto specific proteins. By inducing the expression of the sspB adapter protein gene, these

tagged proteins can then be controllably degraded in real time inside living bacterial cells.

This facilitates the investigation of the biological function of these proteins using a range of

biophysical techniques, but also has potential for exploitation in synthetic biology devices.

A range of unnatural amino acids have also been developed, which utilize different

substituent groups to optimize their physical and chemical properties catered for specific

binding environments, which require a combination of genetic and chemical methods to

integrate into artificial protein structures. A subset of these is genetically encoded synthetic

fluorescent amino acids, used as reporter molecules. These are artificial amino acids that

have a covalently bound fluorescent tag engineered into the substituent group. The method

of tagging is not via chemical conjugation but rather the amino acid is genetically coded

directly into the DNA that codes for a native protein that is to be modified. This essentially

involves modifying one of the nonsense codons that normally do not code for an amino acid

(see Chapter 2). Currently, the brightness and efficiency of these fluorescent amino acids is

still poor for low-​light biophysical applications such as single-​molecule fluorescence micros­

copy studies, as well as there being a limitation of the colors available, but there is certainly

scope for future development.

Larger length scale synthetic biology devices also utilize macromolecular protein

complexes. For example, the protein capsid of virus particles has been used. One such device

has used a thin layer of M13 bacteriophage virus particle to construct a piezoelectric gener­

ator that is sufficient to operate a liquid crystal display.

9.3.6  BIOMIMETIC MATERIALS

Metamaterials are materials engineered to have properties that have not yet been found in

nature. Biomimetic materials are a subset of metamaterials. They are artificial materials, but

they mimic native biological materials and often require several stages of biophysical charac­

terization of their material properties during the bioengineering design and manufacturing

processes. Several existing biostructures have been used as inspiration for some of the bio­

mimetic materials.

The development of new photonic material that is biomimetic to natural butterfly wings

is a good example. Here, biomimetization of butterfly wings can be performed by a series of

metal vapor deposition steps (see Chapter 7). The key step though is actually to use a native