An oligopeptide , often simply called a peptide ( oligo- , “some”), consists of two to twenty amino acids and can include dipeptides , tripeptides , tetrapeptides , and pentapeptides. The major classes of naturally occurring oligopeptides include aeruginosins, cyanopeptolins , microcystins , microviridins , microginins, anabaenopeptins, and cyclamides . Because of their potential toxicity effects in drinking water, microcystins are best studied. A review of some oligopeptides found that the largest class are cyanopeptolins (40.1%), followed by microcystins (13.4%).
The oligopeptide classes are produced by nonribosomal peptides synthases (NRPS), except cyclamides and microviridines are synthesized via ribosomal pathways.
Examples of oligopeptides include:
- Amanitins – Cyclic peptides derived from carpophores of several different mushroom species. They are potent inhibitors of RNA polymerase in most eukaryotic species, inhibiting the production of mRNA and protein synthesis. These peptides are important in the study of transcription. Alpha-amanitin is the main toxin from the species Amanita phalloides , poisonous if ingested by humans or animals.
- Antipen – an oligopeptide produced by various bacteria that acts as a protease inhibitor.
- Ceruletide – A specific decapeptide found in the skin of the Australian green tree frog , Hyla caerulea . Ceruletide has much in common with regard to action and structure to cholecystokinin . It stimulates gastric, bile, and pancreatic secretions; And some smooth muscle . It is used to induce pancreatitis in experimental animal models .
- Glutathione – a tripeptide with multiple roles in cells. It interacts with drugs to make them more soluble for excretion, is a cofactor for some enzymes, is involved in protein disulfide bond rearrangement and reduces peroxidase.
- Lupeptins – a group of acylated oligopeptides produced by actinomycetes that act as protease inhibitors. They are known to inhibit to varying degrees trypsin , plasmin , kallikreins , papain and cathepsins.
- Natropsin – a basic oligopeptide isolated from Streptomyces natropsis . It is cytotoxic and its strong, specific binding to the AT regions of DNA is useful for genetics research.
- Pepsin-N- acylated oligopeptides isolated from culture filtrates of actinomycetes act specifically to inhibit acid proteases such as pepsin and renin.
- Peptide T- N- ( N- ( N (2)-( N- ( N- ( N- ( N – D – Alanyl L -seryl) -L -threonyl)-L- threonyl ) L – threonyl) -L- Asparagus )- L- Tyrosyl) L-Threonine. Octapeptide sharing sequence homology with the HIV envelope protein gp120. It may be useful as an antiviral agent in AIDS therapy. The core pentapeptide sequence, TTNYT, consisting of amino acids 4–8 in peptide T, is the HIV envelope sequence required for attachment to the CD4 receptor.
- Phalloidin – a very toxic polypeptide primarily isolated from Amanita phalloides (Agaricaceae) or death cap; Mushroom poisoning causes fatal liver, kidney and CNS damage; Used in the study of liver damage.
- Teprotide – A man created a nonapeptide (Pyr-Trp-Pro-Arg-Pro-Gln-Ile-Pro-Pro) that is exactly the same as a peptide from snake venom, Bothrops jararaca. It inhibits kininase II and ANGIOTENSIN I and has been proposed as an antihypertensive agent.
- Tuftsin – N (2)-((1-( N (2)- L -Threonyl)- L -lysyl)- L -prolyl)- L –arginine. A tetrapeptide produced in the spleen by enzymatic cleavage of leukophilic gamma-globulin. It specifically stimulates the phagocytic activity of blood polymorphonuclear leukocytes and neutrophils. The peptide is located in the FD fragment of the gamma-globulin molecule.