Cyclic peptide

Cyclic peptides (or cyclic proteins) are polypeptide chains in which the amino termini and carboxyl termini; amino termini and side chain; carboxyl termini and side chain; or side chain and side chain are linked with a covalent bond that generates the ring. A number of cyclic peptides have been discovered in nature and a plethora have been synthesized in the laboratory. Their length ranges from just two amino acid residues to hundreds. These cyclic peptides have several applications in medicine and biology.

Cyclic peptides can be classified according to the types of bonds that comprise the ring.

One interesting property of cyclic peptides is that they tend to be extremely resistant to the process of digestion, enabling them to survive in the human digestive tract. This trait makes cyclic peptides attractive to designers of protein-based drugs that may be used as scaffolds which, in theory, could be engineered to incorporate any arbitrary protein domain of medicinal value, in order to allow those components to be delivered orally. This is especially important for delivery of other proteins that would be destroyed without such implementation. Cyclic peptides are also "rigid" compared to the corresponding linear peptides, and this attribute promotes binding by removing the "entropic penalty".

Examples include:

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