Self-Assembly of Proteins and Peptides and Their Applications in Bionanotechnology and Dentistry - Emerging Nanotechnologies in Dentistry - page 212

Various other methods have been developed to attach peptides and gold nanocrystals [30] .
Crystalline glycylglycine bolaamphiphile peptide tubules and studied the pH-sensitive structural
transformation of the peptide tubules. These bolaamphiphiles undergo self-assembly in solution and
form tubular structures with diameters ranging from 20 nm to 1 μm. The peptide nanotube was coated
with a metalloporphyrin compound. Metalloporphyrins are a group of chemical compounds which
have a metallic group attached to a porphyrin ring [31] . Porphyrins are a group of closely related
tetrapyrollic pigments occurring widely in nature and play a vital role in various biological processes.
The heme component of the hemoglobin is a good example of this group of compounds. The researchers
utilized the electron-transferring property of the metalloporphyrins to bind to the peptide nanotubes and
were able to grow and immobilize the peptide nanotubes on a gold substrate. They also demonstrated
that the peptide nanotubes can be coated with avidin that enabled them to bind to gold surfaces treated
with biotinylated SAMs [32] which can be applied to fabricate nanobiosensors. A wider range of appli-
cations and the design flexibility of self-assembling protein and peptide complexes together with knowl-
edge of cell biology, biochemistry, and molecular biology have enabled scientists to identify potential
newer applications in the field of material science and nanotechnology [33-35] .
13.7 THREE-DIMENSIONAL PEPTIDE MATRIX SCAFFOLDS
A wider variety of self-assembling peptide nanofibers has been utilized to fabricate three-dimensional
peptide matrix scaffolds [13,14,36,37] . One of the main factors influencing the entire process was
the chirality of the peptide molecules. Two molecules are said to be chiral if their mirror images do
not superimpose on each other. One such peptide sequence is the KFE8 peptide complex which is a
natural amphiphilic eight-residue peptide complex [34] . The KFE8 has the peptide chain sequence of
FKFEFKFE ( Figures 13.10 and 13.11 ). This structure represents a group of self-assembling peptides
that spontaneously self-assemble under certain physiological conditions. This peptide molecule self-
assembles in aqueous solution into left-handed helical ribbons when the peptide backbone is twisted in
the opposite direction. The researchers replaced certain amino acids in the hydrophobic side chains with
another amino acid sequence and observed the changes [38] . When a positively charged lysine (Lys)
was replaced by a positively charged arginine (Arg) or when a negatively charged glutamate (Glu) was
replaced by a negatively charged aspartate (Asp), they observed very little changes in the nanofibers that
were formed. But when the positively charged residue was replaced by a negatively charged residue or
FIGURE 13.10
Molecular model of KFE8 peptide.