Cyclic peptides are polypeptides that contain a cyclization- like sequence of connections.This can be achieved by linking the amino and carboxyl ends of peptides, as in cyclosporine; The connection between the amino terminal and the side chain, as in bacitracin; Carboxyl terminal and side chains, such as colistin;Or two side chains or more complex arrangements, as in amanitin. Many cyclic peptides have been found in nature and many others have been synthesized in the laboratory.They range in length from two amino acid residues to hundreds.In nature, they are usually antimicrobial or toxic; In medicine, they have a variety of applications, such as antibiotics and immunosuppressants.Thin layer chromatography (TLC) is a simple method for the detection of cyclopeptides in biomass crude extracts
Cyclic peptides can be classified according to the types of bonds that make up the ring.
Homologous cyclic peptides, such as cyclosporine A, are those in which the rings consist only of normal peptide bonds (i.e., between the carboxyl of one residue and the amine of the other residue).The smallest such substance is 2, 5-diketone piperazine, derived from the cyclopeptide.
Cyclic isopeptides, such as microcystis toxin and bacitracin, contain at least one non-amide bond, such as a bond between the side chain of one residue and the carboxyl group of the other residue.
Cyclic peptides, such as chrysobasidin A and hun-7293, have at least one lactone (ester) bond in place of one of the amides.Some cyclic peptides, such as kahalalide F, theonellapeptolide and didemnin B, are cycled between the c-terminal carboxyl group and the side chains of the Thr or Ser residues in the chain.
Double rings, such as amatoxin amanitin and phallotoxin, contain bridging groups, usually with two side chains.In amatoxins, it forms a sulfoxide bridge between the Trp and Cys residues.Other dicyclic peptides include acanthomycin, triostin A and Celogentin C.
Oxytocin is a noteworthy example of the many cyclic and cyclic peptides that are cysteinized by disulfide bonds between two cysteines.
Cyclic peptides in plants are synthesized in two steps.The translation of linear peptides and subsequent formation of ring structures by protease like enzymes or other means of activity.
Properties and applications
Cyclic peptides are often extremely resistant to the digestive process, allowing them to survive in the human digestive tract.
Valinomycin (technically a depsipeptide)
Different methods for synthesizing cyclic peptides
Skeletal cyclic peptides can be easily assembled by forming an amide bond between the n-terminal amine of the peptide itself and the c-terminal carboxylic acid.Common methods are chemical synthesis and biosynthesis.
2.Side chain Cyclization,
Side chain to side chain is often used to stabilize and select specific conformations and reduce susceptibility to proteolytic degradation.It is selectively protected, and then the side chain of the peptide is deprotected to allow the formation of lactam Bridges between lysine or diaminopropionic acid and glutamate and aspartic acid.
3.CLIPS(Chemical Linkage of Peptides onto Scaffolds) Cyclization
CLIPS technology is based on the chemical connection between linear peptide precursors and activated bromide on molecular scaffolds via the sulfhydryl nucleophilic attack (usually cysteine residue) on linear peptide precursors.
Disulfide bonds are widely found in hormones, enzymes and immunoglobulins and are thought to play an important role in the reconstruction of the conformation of bioactive peptides.Disulfide bonds are often used to modify bioactive peptides to further enhance bioactivity.
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