Chemistry Reference
In-Depth Information
is increased from 12-40 to 55-84 (Cummings and Zoghbi 2000). The excess of
glutamine alters the peptide folding behavior into parallel b-sheet fibers. The secon-
dary structure of nonpathogenic and pathogenic forms of ataxin-3 was monitored
by CD and other spectroscopic measurements (Bevivino and Loll 2001). The
pathogenic form clearly exhibits a b-sheet character, and fibrils were observed
under TEM. In contrast, the normal peptide forms an a-helix rather than a b-sheet
secondary structure.
There have been several efforts at designing peptides that form parallel b-sheets.
The general strategy is to impart an amphiphilic nature into the peptide by using
hydrophobic amino acids as seen in the natural systems described earlier.
Interactions between certain amino acid pairs in adjacent peptide strands have been
found to be favorable for parallel b-sheet formation (Fooks et al. 2006). Electrostatic
interaction between positive and negatively charged amino acids is the most favored
in a parallel b-sheet, followed by Asn-Asn pairing and interactions between
hydrophobic residues. Interaction between Cys pairs is also energetically favored.
Another approach is to include unnatural amino acids, such as g-aminobutyric
acid (Ray, Drew, et al. 2006) or d-aminovaleric acid residues (Banerjee et al.
2005) at the peptide N-terminus. Characterization by FTIR verified the b-sheet
nature of the conformation of the peptides. Depending on the rest of the peptide
sequence, the peptides adopt either parallel or anti-parallel b-sheet, which can be
determined by single crystal X-ray diffraction studies. TEM and scanning electron
microscopy analysis displayed the fibrous morphology of the self-assembled
peptides. Parallel b-sheets can also be generated by linking C- or N-termini of
two beta strands with turn-inducing moieties such as
D
-prolyl-1,1-dimethyl-1,2-
diaminoethane (Fisk and Gellman 2001).
Potential applications of b-sheet forming nanofibers currently focus on the
development of cellular scaffold, templated mineralization for the preparation of
composite materials. Excellent examples in the field of biomedical research have
been demonstrated in some of the previous discussion. The fabrication of molecular
wires is made possible through the “bottom-up” self-assembly approach with
b-sheets as templates. The strong affinity of metals toward peptide-based fibrous
materials is determined by the wide range of chemical functionalities, especially
those capable of coordinating with metals, such as gold, silver, palladium, and
others. Lindquist's group has successfully prepared a conducting wire using a frag-
ment of amyloid fibrous protein (Sup35p) as the biotemplate, showing the conductive
properties of a solid nanowire, such as low resistance and ohmic behavior (Scheibel
et al. 2003). Fu and colleagues (2003) reported another self-assembled amyloid fiber
system that directed the formation of single or double helical arrays of metal particles.
PAs represent a major class of materials that can be utilized in the construction
of inorganic-organic hybrid materials, for example, the nucleation and growth
of HA, silica nanotubes, cadmium sulfide, and so forth. As the most recent update
in biomineralization of nanofibers, Banejee's group (Bose et al. 2007) described a
two-component nongrafting method to fabricate metal particle coated nanofibers
formed by a pseudopeptide. These biotemplated nanowires have potential practical
applications in the field of electroengineering. Related topics can be found in excellent
