Self-Assembling Nanopeptides Become a New Type of Biomaterial - Advances in Polymer Science - page 150

Fig. 1 Fabrication of various peptide materials. Peptide Lego, also called ionic self-
complementary peptide has 16 amino acids, 5 nm in size, with an alternating polar and
non-polar pattern. They form stable b-strand and b-sheet structures, thus the side chains
partition into two sides, one polar and the other non-polar. They undergo self-assembly
to form nanofibers with the non-polar residues inside ( green )andpositive( blue )and
negative ( red ) charged residues forming complementary ionic interactions, like a checker-
board. These nanofibers form interwoven matrices that produce a scaffold hydrogel with
very high water content, 99.5% water (images courtesy of Hidenori Yokoi)

peptide matrices with enhanced strength [35]. The fundamental design prin-
ciples of such self-assembling peptide systems can be readily extended to
polymers and polymer composites, where copolymers can be designed and
produced.

2.3
Molecular Switches

Several peptides have been developed as “molecular switches” in which the
peptides can drastically change their molecular structure. One of the pep-
tides with 16 amino acids, DAR16-IV, has a -sheet structure 5 nm in length

at ambient temperature but can undergo an abrupt structural transition at
high temperatures to form a stable

β

-helical structure 2.5 nm long [13].
Similar structural transformations can be induced by changes in pH. This
suggests that secondary structures of some sequences, especially segments
flanked by clusters of negative charges on the N -terminus and positive
charges on the C -terminus, may undergo drastic conformational transform-
ations under the appropriate conditions. These findings do not only pro-
vide insights into protein-protein interactions during protein folding and the
pathogenesis of some protein conformational diseases, such as Alzheimer's
disease, Gestmann-Straussler-Scheiker syndrome and/or kuru in humans
and scrapie in sheep, cow, mink or elk, as well as certain types of cancer,
all of which are examples of such conformational disorder [34-41], but can
also be developed as molecular switches for a new generation of nanoac-
tuators. Both peptides of DAR16-IV (DADADADARARARARA) and EAK12
(AEAEAEAEAKAK) have a cluster of negatively charged glutamate residues
close to the N -terminus and a cluster of positively charged Arg residues
near the C -terminus. It is well known that all

α

-helices have a helical dipole
moment with a partially negative C -terminus toward a partially positive

α