Cyclic peptides are

polypeptide chains Peptides (, ) are short chains of amino acids linked by peptide bonds. Long chains of amino acids are called proteins. Chains of fewer than twenty amino acids are called oligopeptides, and include dipeptides, tripeptides, and tetrapeptides. A p ...

which contain a circular sequence of bonds. This can be through a connection between the amino and carboxyl ends of the peptide, for example in

cyclosporin Ciclosporin, also spelled cyclosporine and cyclosporin, is a calcineurin inhibitor, used as an immunosuppressant medication. It is a natural product. It is taken orally or intravenously for rheumatoid arthritis, psoriasis, Crohn's disea ...

; a connection between the amino end and a side chain, for example in bacitracin; the carboxyl end and a side chain, for example in

colistin Colistin, also known as polymyxin E, is an antibiotic medication used as a last-resort treatment for multidrug-resistant Gram-negative infections including pneumonia. These may involve bacteria such as ''Pseudomonas aeruginosa'', '' Klebsiella ...

; or two side chains or more complicated arrangements, for example in amanitin. Many cyclic peptides have been discovered in nature and many others have been synthesized in the laboratory. Their length ranges from just two amino acid residues to hundreds. In nature they are frequently antimicrobial or toxic; in medicine they have various applications, for example as antibiotics and immunosuppressive agents.

Thin-Layer Chromatography Thin-layer chromatography (TLC) is a chromatography technique used to separate non-volatile mixtures. Thin-layer chromatography is performed on a sheet of an inert substrate such as glass, plastic, or aluminium foil, which is coated with a t ...

(TLC) is a convenient method to detect cyclic peptides in crude extract from bio-mass.

Classification

Cyclic peptides can be classified according to the types of bonds that comprise the ring. *Homodetic cyclic peptides, such as cyclosporine A, are those in which the ring is composed exclusively of normal peptide bonds (i.e. between the alpha carboxyl of one residue to the alpha amine of another). The smallest such species are 2,5-diketopiperazines, being derived from the cyclisation of a dipeptide. *Cyclic isopeptides contain at least one non-alpha amide linkage, such as a linkage between the side chain of one residue to the alpha carboxyl group of another residue, as in microcystin and bacitracin. *Cyclic depsipeptides, such as aureobasidin A and HUN-7293, have at least one lactone (ester) linkage in place of one of the amides. Some cyclic depsipeptides are cyclized between the C-terminal carboxyl and the side chain of a Thr or Ser residue in the chain, such as kahalalide F, theonellapeptolide, and didemnin B. * Bicyclics such as the amanitins and the

phalloidin Phalloidin belongs to a class of toxins called phallotoxins, which are found in the death cap mushroom ''(Amanita phalloides)''. It is a rigid bicyclic heptapeptide that is lethal after a few days when injected into the bloodstream. The major sy ...

s contain a bridging group, generally between two of the side chains. In the amatoxins, this is formed as a sulfoxide bridge between the Trp and Cys residues. Other bicyclic peptides include echinomycin, triostin A, and Celogentin C. * There are a number of bi and monocyclic peptides which are cyclized through a

disulfide bond In biochemistry, a disulfide (or disulphide in British English) refers to a functional group with the structure . The linkage is also called an SS-bond or sometimes a disulfide bridge and is usually derived by the coupling of two thiol groups. In ...

between two cysteines, oxytocin being a notable example.

Biosynthesis

Cyclic peptides in plants are synthesized via a two-step process; the

translation Translation is the communication of the meaning of a source-language text by means of an equivalent target-language text. The English language draws a terminological distinction (which does not exist in every language) between ''transla ...

of a linear peptide chain, and its subsequent formation into a cyclic structure through activities of a protease-like enzyme or other ways.

Properties and applications

Cyclic peptides tend to be extremely resistant to the process of digestion, making them of interest to scientists working on novel oral medications. Examples include: * Amanitins * Bacitracin *

Colistin Colistin, also known as polymyxin E, is an antibiotic medication used as a last-resort treatment for multidrug-resistant Gram-negative infections including pneumonia. These may involve bacteria such as ''Pseudomonas aeruginosa'', '' Klebsiella ...

Ciclosporin Ciclosporin, also spelled cyclosporine and cyclosporin, is a calcineurin inhibitor, used as an immunosuppressant medication. It is a natural product. It is taken orally or intravenously for rheumatoid arthritis, psoriasis, Crohn's disease ...

Dactinomycin Dactinomycin, also known as actinomycin D, is a chemotherapy medication used to treat a number of types of cancer. This includes Wilms tumor, rhabdomyosarcoma, Ewing's sarcoma, trophoblastic neoplasm, testicular cancer, and certain types of ...

Daptomycin Daptomycin, sold under the brand name Cubicin among others, is a lipopeptide antibiotic used in the treatment of systemic and life-threatening infections caused by Gram-positive organisms. Daptomycin was removed from the World Health Organiza ...

Gramicidin S Gramicidin S or Gramicidin Soviet is an antibiotic that is effective against some gram-positive and gram-negative bacteria as well as some fungi. It is a derivative of gramicidin, produced by the gram-positive bacterium '' Brevibacillus brevis ...

* Hymenistatin * Microcystins *

Nisin Nisin is a polycyclic antibacterial peptide produced by the bacterium ''Lactococcus lactis'' that is used as a food preservative. It has 34 amino acid residues, including the uncommon amino acids lanthionine (Lan), methyllanthionine (MeLan), di ...

Nodularin Nodularins are potent toxins produced by the cyanobacterium '' Nodularia spumigena'', among others. This aquatic, photosynthetic cyanobacterium forms visible colonies that present as algal blooms in brackish water bodies throughout the world. The ...

Octreotide Octreotide, sold under the brand name Sandostatin among others, is an octapeptide that mimics natural somatostatin pharmacologically, though it is a more potent inhibitor of growth hormone, glucagon, and insulin than the natural hormone. It was ...

Polymyxin B Polymyxin B, sold under the brand name Poly-Rx among others, is an antibiotic used to treat meningitis, pneumonia, sepsis, and urinary tract infections. While it is useful for many Gram negative infections, it is not useful for Gram positive inf ...

Pristinamycin Pristinamycin ( INN), also spelled pristinamycine, is an antibiotic used primarily in the treatment of staphylococcal infections, and to a lesser extent streptococcal infections. It is a streptogramin group antibiotic, similar to virginiamycin, d ...

Valinomycin Valinomycin is a naturally occurring dodecadepsipeptide used in the transport of potassium and as an antibiotic. Valinomycin is obtained from the cells of several ''Streptomyces'' species, '' S. fulvissimus'' being a notable one. It is a member o ...

(technically a depsipeptide) *

Vancomycin Vancomycin is a glycopeptide antibiotic medication used to treat a number of bacterial infections. It is recommended intravenously as a treatment for complicated skin infections, bloodstream infections, endocarditis, bone and joint infections, ...

* Viscumamide * Yunnanin A

References

External links

Cybase
* {{MeshName, Cyclic+Peptides Peripheral membrane proteins

Classification

Biosynthesis

Properties and applications

See also

References

External links