Long before chemists made peptides, living things were using them as signals, defences and weapons. Natural peptides are the main source of ideas for peptide research.
Peptide hormones
Many of the body's chemical messengers are peptides. They are released in one tissue, travel through the blood, and act on receptors elsewhere.
| Peptide | Size | Made in | Main role |
|---|---|---|---|
| Insulin | 51 residues (two chains) | Pancreatic β-cells | Lowers blood glucose |
| Glucagon | 29 residues | Pancreatic α-cells | Raises blood glucose |
| GLP-1 | ~30 residues | Intestinal L-cells | Incretin hormone; boosts insulin release after meals |
| Oxytocin | 9 residues (cyclic) | Hypothalamus | Childbirth, lactation, social bonding |
| Vasopressin | 9 residues (cyclic) | Hypothalamus | Water balance and blood pressure |
| Ghrelin | 28 residues | Stomach | Hunger signalling |
Natural peptide hormones typically last only minutes in the blood, so their signals are brief and tightly controlled. Much of the work on longer-lasting synthetic peptides is about extending that.
Neuropeptides
Neurons release peptides as well as classical neurotransmitters. Examples include endorphins and enkephalins, the body's own opioids, substance P, involved in pain signalling, and neuropeptide Y, involved in appetite and stress. Neuropeptides tend to act more slowly and over longer distances than small-molecule transmitters.
Small but essential: glutathione
Glutathione is a tripeptide (glutamate–cysteine–glycine) found in almost every cell. It acts as a key antioxidant, using its cysteine thiol group to neutralise reactive oxygen species.
Defensive peptides
Plants, insects, amphibians and mammals all produce antimicrobial peptides as a first line of defence against infection. Humans make defensins and the cathelicidin LL-37. Frog skin is a particularly rich source: the magainins were discovered on the African clawed frog in 1987. See our article on antimicrobial peptides.
Venoms: nature's peptide libraries
Snake, spider, scorpion and cone snail venoms are complex cocktails of peptides that evolved to hit specific ion channels and receptors very precisely. They've given research some valuable tools and medicines:
- Captopril, an early blood-pressure drug, was designed from peptides in Brazilian pit viper venom.
- Exenatide is based on exendin-4 from Gila monster saliva.
- Ziconotide is a synthetic version of a cone snail toxin.
Microbial peptides
Bacteria and fungi make peptides, often cyclic and containing unusual amino acids, to compete with each other. Many antibiotics come from them. Read more in Cyclic peptides in nature.
Related articles
- A brief history of peptide science
- How peptide receptors work: GPCRs explained
- Peptide structure: from sequence to shape
Sources and further reading
- Muttenthaler M, King GF, Adams DJ, Alewood PF. Trends in peptide drug discovery. Nat Rev Drug Discov 2021;20:309–325. doi:10.1038/s41573-020-00135-8 · PMID: 33536635
- Zasloff M. Magainins, a class of antimicrobial peptides from Xenopus skin. PNAS 1987;84:5449–5453. doi:10.1073/pnas.84.15.5449 · PMID: 3299384
- King GF. Venoms as a platform for human drugs: translating toxins into therapeutics. Expert Opin Biol Ther 2011;11:1469–1484. doi:10.1517/14712598.2011.621940 · PMID: 21939428
- Cushman DW, Ondetti MA. History of the design of captopril and related inhibitors of angiotensin converting enzyme. Hypertension 1991;17:589–592. doi:10.1161/01.HYP.17.4.589 · PMID: 2013486