Foldamers have specific properties that make them superior to conventional peptides. Foldamers are self-organizing and can form higher order structures.
Structure and Features of Beta Foldamers
They are stabilized due to the presence of hydrogen bonds, while the torsion due to backbone and side chain interactions dictate the three dimensional structure. The main features of foldamers are that they have a large surface area which increases its binding potential, and they are highly resistant to proteolytic degradation compared to their peptide counterparts.
Types of Foldamers
Foldamers are of the following types: peptoids, aromatic and aliphatic oligoamides. While peptoids have N-substituted polyglycines as side chains on the nitrogen atom, aromatic oligoamides have aromatic or heteroaromatic rings linked by amide bonds, Peptoids are less complex structurally and thus easier to design. Aliphatic oligoamides generate α, β, γ, or δ peptides based on where the amide groups that form the peptide bonds are located. Different kinds of foldamers, including individual α or β peptide foldamers or mixed sequences such as α/β foldamers also exist.
Applications of Beta Foldamers
With the rise in antibiotic resistant strains of bacteria, there is a need to invest further in finding newer antimicrobial molecules. Antimicrobial peptides have been shown to act as antibiotics where they can disrupt the cell membrane and lead to death of the bacteria. Interestingly, no antibiotic resistance was observed in response to peptide foldamers. These peptides can be administered via three ways: intravenously, intraperitoneally, and orally. Studies have shown that gastrointestinal infections can be treated using peptoid antibacterial preparations.
Cell Penetrating Foldamers
As peptides can enter the cell, they can be used to deliver drugs and proteins or to disrupt the cell membranes. Foldamer peptides can penetrate cell membranes 3−30 times more effectively than original peptides.
Treatment of AIDS and Malaria
During transcription of HIV, the TAT protein interacts with a hairpin RNA segment TAR or transcriptional activator-responsive element. A β-peptide that was a TAT analogue and TAR-binding was designed to penetrate the cell membranes in an HIV infected cell.
Another major advancement due to the cell penetrating ability of the foldamers has been in the treatment of malaria caused by Plasmodium falciparum. The β-peptide foldamers cannot cross the cell membrane of healthy erythrocytes; however, they can pass the membranes of cells infected by Plasmodium. Thus, they may present a new way to treat malaria.
Alzheimer’s disease affects 20% of population between age 75−84 years. There is accumulation of β-amyloid in this disease in the brain, although it is not clear if it is the cause or consequence of the disease. It was found that a β-peptide--dendrimer conjugate complex could bind to the toxic β-amyloid oligomers and neutralize it. Also, the oligomerization was inhibited in ex vivo measurements. Thus, β-peptide foldamers could provide a novel and potent method against Alzheimer’s disease.
Side Effects of Beta Peptides
Although effective, β peptides also exhibited significant hemolytic activity which subsequently damaged human RBCs. This effect was found to be due to the hydrophobic nature of the β peptides and addition of positively charged cyclic groups could reduce its hemolytic activity. Additionally, the positive charges also increased the affinity towards the negatively charged bacterial membranes and lowered the affinity towards hydrophobic erythrocytic membrane.