Peptide Nanotubes: A Crystallographic Approach
95
The potential use of self-assembled peptide nanostructures as novel materials has
been demonstrated in the field of biomaterials and use for carrier-mediated drug delivery, tissue engineering, antimicrobial agents, imaging tools, energy storage, biomineralization. The self-assembled peptides have been exploited for generating bioinspired nanostructures, including nanotubes, nanofibers, nanospheres, nanobelts,
and hydrogels.
While there have been many studies of protein-coded amino acids engaged in
molecular self-assembly, not much work has been done on molecular self-assembly
formation utilizing non-coded amino acids. The incorporation of non-coded amino
acids in the molecular self-assembly of a dipeptide motif may offer an added
advantage in terms of variety and stability.
2 Back Bone Conformation Constraining Amino Acids
There are varieties of non-coded, conformation constraining amino acids and many
of them occur in natural proteins and peptides from microbial sources. α, βDehydroamino acids (a.a), α,α-disubstituted amino acids constitute the class of
conformation constraining amino acids. The ability of these amino acids to dictate the folding of the polypeptide chains has been well established (Balaram 1999;
DeGrado 1988; Jain and Chauhan 1996; Karle 1992; Mathur et al. 2004; Venkatraman 2001). Furthermore, the development of a biosynthetic method for site-specific
incorporation of unnatural amino acids into proteins (Liu and Schultz 1999; Mendel
1995; Noren et al. 1989) is promising to promote a great interest in using these amino
acids in protein design.
Among the conformation constraining amino acids, α, β-dehydrophenylalanine
(Phe) a member of α, β-dehydroamino acid group is being extensively used in the
modular approach to synthetic protein design. Herein, the possibility of incorporating α, β-dehydrophenylalanine (Phe) residue in the peptide sequences for
studies in molecular self -assembly has been explored.
2.1 α, β-dehydroamino Acids
These are the derivatives of protein amino acids (saturated amino acids) with a double
bond between C
α and C
β atoms (Fig. 1) and are represented by a prefix symbol ‘’.
They are also referred as α, β-unsaturated amino acids and are frequently found in
natural peptides of microbial, fungal metabolite sources (Aubry et al. 1985; Gross and
Morell 1967; Jung 1991), and in some proteins, e.g. histidine ammonia-lyase from
bacterial and mammalian, and phenylalanine ammonia-lyase from plants (Noda et al.
1983). Peptides containing these amino acids are synthesized in the ribosome via a
precursor protein followed by enzymatic modifications (Allgaier et al. 1986). Polycyclic peptide antibiotics called lantibiotics such as nisin, subtilin, epidermin, and
95
The potential use of self-assembled peptide nanostructures as novel materials has
been demonstrated in the field of biomaterials and use for carrier-mediated drug delivery, tissue engineering, antimicrobial agents, imaging tools, energy storage, biomineralization. The self-assembled peptides have been exploited for generating bioinspired nanostructures, including nanotubes, nanofibers, nanospheres, nanobelts,
and hydrogels.
While there have been many studies of protein-coded amino acids engaged in
molecular self-assembly, not much work has been done on molecular self-assembly
formation utilizing non-coded amino acids. The incorporation of non-coded amino
acids in the molecular self-assembly of a dipeptide motif may offer an added
advantage in terms of variety and stability.
2 Back Bone Conformation Constraining Amino Acids
There are varieties of non-coded, conformation constraining amino acids and many
of them occur in natural proteins and peptides from microbial sources. α, βDehydroamino acids (a.a), α,α-disubstituted amino acids constitute the class of
conformation constraining amino acids. The ability of these amino acids to dictate the folding of the polypeptide chains has been well established (Balaram 1999;
DeGrado 1988; Jain and Chauhan 1996; Karle 1992; Mathur et al. 2004; Venkatraman 2001). Furthermore, the development of a biosynthetic method for site-specific
incorporation of unnatural amino acids into proteins (Liu and Schultz 1999; Mendel
1995; Noren et al. 1989) is promising to promote a great interest in using these amino
acids in protein design.
Among the conformation constraining amino acids, α, β-dehydrophenylalanine
(Phe) a member of α, β-dehydroamino acid group is being extensively used in the
modular approach to synthetic protein design. Herein, the possibility of incorporating α, β-dehydrophenylalanine (Phe) residue in the peptide sequences for
studies in molecular self -assembly has been explored.
2.1 α, β-dehydroamino Acids
These are the derivatives of protein amino acids (saturated amino acids) with a double
bond between C
α and C
β atoms (Fig. 1) and are represented by a prefix symbol ‘’.
They are also referred as α, β-unsaturated amino acids and are frequently found in
natural peptides of microbial, fungal metabolite sources (Aubry et al. 1985; Gross and
Morell 1967; Jung 1991), and in some proteins, e.g. histidine ammonia-lyase from
bacterial and mammalian, and phenylalanine ammonia-lyase from plants (Noda et al.
1983). Peptides containing these amino acids are synthesized in the ribosome via a
precursor protein followed by enzymatic modifications (Allgaier et al. 1986). Polycyclic peptide antibiotics called lantibiotics such as nisin, subtilin, epidermin, and