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A. Bagaria and S. Ramakumar
undergo spontaneous organization into a stable macroscopic structure using noncovalent interactions (Lehn 1993; Whitesides and Grzybowski 2002). The interactions typically include H-bonds, water-mediated H-bonds, ionic bonds, hydrophobic
and Vander Waals interactions (Pauling 1939). These forces alone may not suffice
for the overall organization of the defined structures; the cooperation of interactions
can yield highly stable and robust structures.
Supramolecular assemblies of small biomolecules have generated a lot of interest,
as the chemical modifications can offer large variations. Numerous reports of tubular
assemblies of carbon (Ajayan and Ebbesen 1997; Iijima 1991) boron nitrite (Chopra
et al. 1995), zeolites (Dessau et al. 1990; Meier and Olson 1988) and carbohydratebased nanotubes (Harada et al. 1993) have catapulted the research in this vast area
of material science research. Parang et al. suggested that the designed cyclic D, Lα-peptides could potentially self-assemble in bacterial membranes, increasing the
membrane permeability and thus exhibiting antibacterial activity.
The peptide-based nanostructures of interest as they offer many opportunities for
chemical variations, and hence control, in designing molecular assemblies, which
have been successfully demonstrated to be good models for ion channels and membrane pores (Engels et al. 1995; Ghadiri et al. 1994; Granja and Ghadiri 1994; Hauser
and Zhang 2010; Kim et al. 1998). The crystal structure of many hydrophobic dipeptides have pores filled with the crystallizing solvent molecules. This has opened
avenues for the use of such structure as biosensors, biocatalysts and specific molecular recognition platforms (Akazome et al. 2000; Gazit 2007; Gorbitz 2001, 2002a,
b, 2003, 2006; Gorbitz et al. 2005; Mahler 2006; Reches and Gazit 2003). To exemplify, hollow tubular structures act as conduits of chemical information in the form of
transmembrane ion channels (Nonner and Eisenberg 1998) and provide closed reaction chambers as demonstrated by protein folding chaperonins (Xu and Sigler 1998)
and protein degradation enzymes (Voges et al. 1999; Zwickl et al. 1999). Attempts
to generate synthetic water channels that mimic the aquaporin channel have met
with some success (Liu et al. 2005; Sidhu et al. 2004; Videnova-Adrabiska 2002). A
zwitterionic helical tube of nanodimensions that mimics aquaporin with water incorporated inside the channel has been studied by solid-state
2 HNMR spectroscopy and
X-ray crystallography (Fei et al. 2005; Middleton et al. 2013).
Pioneering work on tube-like structures, invariably formed by the stacking of
cyclic molecules through intermolecular hydrogen bonds between functional groups
in the peptide backbones, has been carried out by Ghadiri and co-workers for cyclic
peptides with 8–12 residues (Engels et al. 1995; Ghadiri et al. 1993, 1994; Kim et al.
1998; Sidhu et al. 2004). Several short peptides have a pronounced tendency to form
long needles or fibres when being crystallized from aqueous or non-aqueous solution. A well-ordered and discrete peptide nanotubes formed by the self-assembly of
the diphenylalanine as core recognition motif of Alzheimer’s β-amyloid polypeptide
(Abromovic et al. 2006; Reches and Gazit 2003), has further to the use of peptidebased nanostructures for the design of folded and self-organized modules (Gorbitz
2006). However, the stability check of the peptide-based structures under different physical, chemical and biochemical conditions needs to be established before
utilizing them as biomolecular entities.
A. Bagaria and S. Ramakumar
undergo spontaneous organization into a stable macroscopic structure using noncovalent interactions (Lehn 1993; Whitesides and Grzybowski 2002). The interactions typically include H-bonds, water-mediated H-bonds, ionic bonds, hydrophobic
and Vander Waals interactions (Pauling 1939). These forces alone may not suffice
for the overall organization of the defined structures; the cooperation of interactions
can yield highly stable and robust structures.
Supramolecular assemblies of small biomolecules have generated a lot of interest,
as the chemical modifications can offer large variations. Numerous reports of tubular
assemblies of carbon (Ajayan and Ebbesen 1997; Iijima 1991) boron nitrite (Chopra
et al. 1995), zeolites (Dessau et al. 1990; Meier and Olson 1988) and carbohydratebased nanotubes (Harada et al. 1993) have catapulted the research in this vast area
of material science research. Parang et al. suggested that the designed cyclic D, Lα-peptides could potentially self-assemble in bacterial membranes, increasing the
membrane permeability and thus exhibiting antibacterial activity.
The peptide-based nanostructures of interest as they offer many opportunities for
chemical variations, and hence control, in designing molecular assemblies, which
have been successfully demonstrated to be good models for ion channels and membrane pores (Engels et al. 1995; Ghadiri et al. 1994; Granja and Ghadiri 1994; Hauser
and Zhang 2010; Kim et al. 1998). The crystal structure of many hydrophobic dipeptides have pores filled with the crystallizing solvent molecules. This has opened
avenues for the use of such structure as biosensors, biocatalysts and specific molecular recognition platforms (Akazome et al. 2000; Gazit 2007; Gorbitz 2001, 2002a,
b, 2003, 2006; Gorbitz et al. 2005; Mahler 2006; Reches and Gazit 2003). To exemplify, hollow tubular structures act as conduits of chemical information in the form of
transmembrane ion channels (Nonner and Eisenberg 1998) and provide closed reaction chambers as demonstrated by protein folding chaperonins (Xu and Sigler 1998)
and protein degradation enzymes (Voges et al. 1999; Zwickl et al. 1999). Attempts
to generate synthetic water channels that mimic the aquaporin channel have met
with some success (Liu et al. 2005; Sidhu et al. 2004; Videnova-Adrabiska 2002). A
zwitterionic helical tube of nanodimensions that mimics aquaporin with water incorporated inside the channel has been studied by solid-state
2 HNMR spectroscopy and
X-ray crystallography (Fei et al. 2005; Middleton et al. 2013).
Pioneering work on tube-like structures, invariably formed by the stacking of
cyclic molecules through intermolecular hydrogen bonds between functional groups
in the peptide backbones, has been carried out by Ghadiri and co-workers for cyclic
peptides with 8–12 residues (Engels et al. 1995; Ghadiri et al. 1993, 1994; Kim et al.
1998; Sidhu et al. 2004). Several short peptides have a pronounced tendency to form
long needles or fibres when being crystallized from aqueous or non-aqueous solution. A well-ordered and discrete peptide nanotubes formed by the self-assembly of
the diphenylalanine as core recognition motif of Alzheimer’s β-amyloid polypeptide
(Abromovic et al. 2006; Reches and Gazit 2003), has further to the use of peptidebased nanostructures for the design of folded and self-organized modules (Gorbitz
2006). However, the stability check of the peptide-based structures under different physical, chemical and biochemical conditions needs to be established before
utilizing them as biomolecular entities.