HOME

TheInfoList



OR:

Peptides (, ) are short chains of
amino acid Amino acids are organic compounds that contain both amino and carboxylic acid functional groups. Although hundreds of amino acids exist in nature, by far the most important are the alpha-amino acids, which comprise proteins. Only 22 alpha a ...
s linked by peptide bonds. Long chains of amino acids are called proteins. Chains of fewer than twenty amino acids are called
oligopeptide An oligopeptide, often just called peptide ('' oligo-'', "a few"), consists of two to twenty amino acids and can include dipeptides, tripeptides, tetrapeptides, and pentapeptides. Some of the major classes of naturally occurring oligopeptides in ...
s, and include dipeptides,
tripeptide A tripeptide is a peptide derived from three amino acids joined by two or sometimes three peptide bonds. As for proteins, the function of peptides is determined by the constituent amino acids and their sequence. The simplest tripeptide is glycine ...
s, and
tetrapeptide A tetrapeptide is a peptide, classified as an oligopeptide, since it only consists of four amino acids joined by peptide bonds. Many tetrapeptides are pharmacologically active, often showing affinity and specificity for a variety of receptors in p ...
s. A polypeptide is a longer, continuous, unbranched peptide chain. Hence, peptides fall under the broad chemical classes of biological polymers and oligomers, alongside nucleic acids, oligosaccharides, polysaccharides, and others. A polypeptide that contains more than approximately 50 amino acids is known as a
protein Proteins are large biomolecules and macromolecules that comprise one or more long chains of amino acid residues. Proteins perform a vast array of functions within organisms, including catalysing metabolic reactions, DNA replication, res ...
. Proteins consist of one or more polypeptides arranged in a biologically functional way, often bound to
ligand In coordination chemistry, a ligand is an ion or molecule ( functional group) that binds to a central metal atom to form a coordination complex. The bonding with the metal generally involves formal donation of one or more of the ligand's elec ...
s such as coenzymes and cofactors, or to another protein or other macromolecule such as DNA or RNA, or to complex macromolecular assemblies. Amino acids that have been incorporated into peptides are termed residues. A water molecule is released during formation of each amide bond.. All peptides except cyclic peptides have an N-terminal (amine group) and
C-terminal The C-terminus (also known as the carboxyl-terminus, carboxy-terminus, C-terminal tail, C-terminal end, or COOH-terminus) is the end of an amino acid chain (protein or polypeptide), terminated by a free carboxyl group (-COOH). When the protein is ...
(carboxyl group) residue at the end of the peptide (as shown for the tetrapeptide in the image).


Classes

There are numerous types of peptides that have been classified according to their sources and functions. According to the Handbook of Biologically Active Peptides, some groups of peptides include plant peptides, bacterial/ antibiotic peptides, fungal peptides, invertebrate peptides, amphibian/skin peptides, venom peptides, cancer/anticancer peptides, vaccine peptides, immune/inflammatory peptides, brain peptides, endocrine peptides, ingestive peptides, gastrointestinal peptides, cardiovascular peptides, renal peptides, respiratory peptides,
opiate peptide An opiate, in classical pharmacology, is a substance derived from opium. In more modern usage, the term ''opioid'' is used to designate all substances, both natural and synthetic, that bind to opioid receptors in the brain (including antagonist ...
s, neurotrophic peptides, and blood–brain peptides. Some ribosomal peptides are subject to proteolysis. These function, typically in higher organisms, as
hormone A hormone (from the Greek participle , "setting in motion") is a class of signaling molecules in multicellular organisms that are sent to distant organs by complex biological processes to regulate physiology and behavior. Hormones are require ...
s and signaling molecules. Some microbes produce peptides as antibiotics, such as
microcin Microcins are very small bacteriocins, composed of relatively few amino acids. For this reason, they are distinct from their larger protein cousins. The classic example is microcin V, of ''Escherichia coli''. Subtilosin A is another bacterioci ...
s and
bacteriocin Bacteriocins are proteinaceous or peptidic toxins produced by bacteria to inhibit the growth of similar or closely related bacterial strain(s). They are similar to yeast and paramecium killing factors, and are structurally, functionally, and ec ...
s. Peptides frequently have post-translational modifications such as phosphorylation, hydroxylation,
sulfonation Aromatic sulfonation is an organic reaction in which a hydrogen atom on an arene is replaced by a sulfonic acid functional group in an electrophilic aromatic substitution. Aryl sulfonic acids are used as detergents, dye, and drugs. Stoichiometry a ...
, palmitoylation, glycosylation, and
disulfide 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 ...
formation. In general, peptides are linear, although
lariat A lasso ( or ), also called lariat, riata, or reata (all from Castilian, la reata 're-tied rope'), is a loop of rope designed as a restraint to be thrown around a target and tightened when pulled. It is a well-known tool of the Spanish an ...
structures have been observed. More exotic manipulations do occur, such as racemization of L-amino acids to D-amino acids in
platypus venom The platypus is one of the few living mammals to produce venom. The venom is made in venom glands that are connected to hollow spurs on their hind legs; it is primarily made during the mating season. While the venom's effects are described as e ...
. '' Nonribosomal peptides'' are assembled by
enzyme Enzymes () are proteins that act as biological catalysts by accelerating chemical reactions. The molecules upon which enzymes may act are called substrates, and the enzyme converts the substrates into different molecules known as products ...
s, not the ribosome. A common non-ribosomal peptide is
glutathione Glutathione (GSH, ) is an antioxidant in plants, animals, fungi, and some bacteria and archaea. Glutathione is capable of preventing damage to important cellular components caused by sources such as reactive oxygen species, free radicals, pe ...
, a component of the antioxidant defenses of most aerobic organisms. Other nonribosomal peptides are most common in
unicellular organism A unicellular organism, also known as a single-celled organism, is an organism that consists of a single cell, unlike a multicellular organism that consists of multiple cells. Organisms fall into two general categories: prokaryotic organisms a ...
s,
plant Plants are predominantly photosynthetic eukaryotes of the kingdom Plantae. Historically, the plant kingdom encompassed all living things that were not animals, and included algae and fungi; however, all current definitions of Plantae exclu ...
s, and
fungi A fungus ( : fungi or funguses) is any member of the group of eukaryotic organisms that includes microorganisms such as yeasts and molds, as well as the more familiar mushrooms. These organisms are classified as a kingdom, separately from ...
and are synthesized by modular enzyme complexes called ''nonribosomal peptide synthetases''. These complexes are often laid out in a similar fashion, and they can contain many different modules to perform a diverse set of chemical manipulations on the developing product. These peptides are often cyclic and can have highly complex cyclic structures, although linear nonribosomal peptides are also common. Since the system is closely related to the machinery for building fatty acids and
polyketide Polyketides are a class of natural products derived from a precursor molecule consisting of a chain of alternating ketone (or reduced forms of a ketone) and methylene groups: (-CO-CH2-). First studied in the early 20th century, discovery, biosynth ...
s, hybrid compounds are often found. The presence of
oxazoles Oxazole is the parent compound for a vast class of heterocyclic aromatic organic compounds. These are azoles with an oxygen and a nitrogen separated by one carbon. Oxazoles are aromatic compounds but less so than the thiazoles. Oxazole is a weak ...
or
thiazoles Thiazole, or 1,3-thiazole, is a heterocyclic compound that contains both sulfur and nitrogen. The term 'thiazole' also refers to a large family of derivatives. Thiazole itself is a pale yellow liquid with a pyridine-like odor and the molecular fo ...
often indicates that the compound was synthesized in this fashion. ' are derived from animal milk or meat digested by proteolysis. In addition to containing small peptides, the resulting material includes fats, metals, salts, vitamins, and many other biological compounds. Peptones are used in nutrient media for growing bacteria and fungi. ''Peptide fragments'' refer to fragments of proteins that are used to identify or quantify the source protein. Often these are the products of enzymatic degradation performed in the laboratory on a controlled sample, but can also be forensic or paleontological samples that have been degraded by natural effects.


Chemical synthesis


Example families

The peptide families in this section are ribosomal peptides, usually with hormonal activity. All of these peptides are synthesized by cells as longer "propeptides" or "proproteins" and truncated prior to exiting the cell. They are released into the bloodstream where they perform their signaling functions.


Antimicrobial peptides

*
Magainin The magainins are a class of antimicrobial peptides found in the African clawed frog (''Xenopus laevis''). The peptides are cationic, generally lack a stable conformation in water but form amphipathic α-helix in membranes; their mechanism agains ...
family * Cecropin family *
Cathelicidin Cathelicidin antimicrobial peptide (CAMP) is a polypeptide that is primarily stored in the lysosomes of macrophages and polymorphonuclear leukocytes (PMNs); in humans, the ''CAMP'' gene encodes the peptide precursor CAP-18 (18 kDa), which is proce ...
family * Defensin family


Tachykinin peptides

*
Substance P Substance P (SP) is an undecapeptide (a peptide composed of a chain of 11 amino acid residues) and a member of the tachykinin neuropeptide family. It is a neuropeptide, acting as a neurotransmitter and as a neuromodulator. Substance P and its clo ...
* Kassinin * Neurokinin A * Eledoisin *
Neurokinin B Neurokinin B (NKB) belongs in the family of tachykinin peptides. Neurokinin B is implicated in a variety of human functions and pathways such as the secretion of gonadotropin-releasing hormone. Additionally, NKB is associated with pregnancy in fem ...


Vasoactive intestinal peptides

*
VIP A very important person or personage (VIP or V.I.P.) is a person who is accorded special privileges due to their high social status, influence or importance. The term was not common until sometime after World War 2 by RAF pilots. Examples inc ...
(''Vasoactive Intestinal Peptide''; PHM27) * PACAP ''Pituitary Adenylate Cyclase Activating Peptide'' *
Peptide PHI Peptide PHI, also known as peptide histidine isoleucine, is a peptide which functions as a hormone. This peptide contains a composition of 27 amino acids with histidine on the N-terminus and isoleucine on the C-terminus. It was originally isolated f ...
27 (''Peptide Histidine Isoleucine 27'') * GHRH 1-24 ''(Growth Hormone Releasing Hormone 1-24)'' * Glucagon * Secretin


Pancreatic polypeptide-related peptides

* NPY ''(NeuroPeptide Y) * PYY ''(Peptide YY)'' * APP ''(Avian Pancreatic Polypeptide)'' * PPY ''Pancreatic PolYpeptide''


Opioid peptides

* Proopiomelanocortin (POMC) peptides * Enkephalin pentapeptides *
Prodynorphin Prodynorphin, also known as proenkephalin B, is an opioid polypeptide hormone involved with chemical signal transduction and cell communication. The gene for prodynorphin is expressed in the endometrium and the striatum, and its gene map locus is 20 ...
peptides


Calcitonin peptides

* Calcitonin *
Amylin Amylin, or islet amyloid polypeptide (IAPP), is a 37-residue peptide hormone. It is co-secreted with insulin from the pancreatic β-cells in the ratio of approximately 100:1 (insulin:amylin). Amylin plays a role in glycemic regulation by sl ...
* AGG01


Self-assembling peptides

* Aromatic short peptides * Biomimetic peptides * Peptide amphiphiles *Peptide dendrimers


Other peptides

* B-type Natriuretic Peptide (BNP) - produced in the myocardium and useful in medical diagnosis * Lactotripeptides - Lactotripeptides might reduce blood pressure, although the evidence is mixed. * Peptidic components from traditional Chinese medicine Colla Corii Asini in hematopoiesis.


Terminology


Length

Several terms related to peptides have no strict length definitions, and there is often overlap in their usage: * A ''polypeptide'' is a single linear chain of many amino acids (any length), held together by amide bonds. * A ''
protein Proteins are large biomolecules and macromolecules that comprise one or more long chains of amino acid residues. Proteins perform a vast array of functions within organisms, including catalysing metabolic reactions, DNA replication, res ...
'' consists of one or more polypeptides (more than about 50 amino acids long). * An ''
oligopeptide An oligopeptide, often just called peptide ('' oligo-'', "a few"), consists of two to twenty amino acids and can include dipeptides, tripeptides, tetrapeptides, and pentapeptides. Some of the major classes of naturally occurring oligopeptides in ...
'' consists of only a few amino acids (between two and twenty).


Number of amino acids

Peptides and proteins are often described by the number of amino acids in their chain, e.g. a protein with 158 amino acids may be described as a "158 amino-acid-long protein". Peptides of specific shorter lengths are named using
IUPAC numerical multiplier The numerical multiplier (or multiplying affix) in IUPAC nomenclature indicates how many particular atoms or functional groups are attached at a particular point in a molecule. The affixes are derived from both Latin and Greek. Compound aff ...
prefixes: * A ''
monopeptide Peptides (, ) are short chains of amino acids linked by peptide bonds. Long chains of amino acids are called Protein, proteins. Chains of fewer than twenty amino acids are called oligopeptides, and include dipeptides, tripeptides, and tetrapepti ...
'' has one amino acid. * A '' dipeptide'' has two amino acids. * A ''
tripeptide A tripeptide is a peptide derived from three amino acids joined by two or sometimes three peptide bonds. As for proteins, the function of peptides is determined by the constituent amino acids and their sequence. The simplest tripeptide is glycine ...
'' has three amino acids. * A ''
tetrapeptide A tetrapeptide is a peptide, classified as an oligopeptide, since it only consists of four amino acids joined by peptide bonds. Many tetrapeptides are pharmacologically active, often showing affinity and specificity for a variety of receptors in p ...
'' has four amino acids. * A ''pentapeptide'' has five amino acids. (''e.g.'', enkephalin). * A ''hexapeptide'' has six amino acids. (''e.g.'', angiotensin IV). * A ''heptapeptide'' has seven amino acids. (''e.g.'', spinorphin). * An ''octapeptide'' has eight amino acids (''e.g.'', angiotensin II). * A ''nonapeptide'' has nine amino acids (''e.g.'', oxytocin). * A ''decapeptide'' has ten amino acids (''e.g.'',
gonadotropin-releasing hormone Gonadotropin-releasing hormone (GnRH) is a releasing hormone responsible for the release of follicle-stimulating hormone (FSH) and luteinizing hormone (LH) from the anterior pituitary. GnRH is a tropic peptide hormone synthesized and release ...
and
angiotensin I Angiotensin is a peptide hormone that causes vasoconstriction and an increase in blood pressure. It is part of the renin–angiotensin system, which regulates blood pressure. Angiotensin also stimulates the release of aldosterone from the a ...
). * A ''undecapeptide'' has eleven amino acids (''e.g.'',
substance P Substance P (SP) is an undecapeptide (a peptide composed of a chain of 11 amino acid residues) and a member of the tachykinin neuropeptide family. It is a neuropeptide, acting as a neurotransmitter and as a neuromodulator. Substance P and its clo ...
). The same words are also used to describe a group of residues in a larger polypeptide (''e.g.'', RGD motif).


Function

* A '' neuropeptide'' is a peptide that is active in association with neural tissue. * A ''
lipopeptide A lipopeptide is a molecule consisting of a lipid connected to a peptide. They are able to self-assemble into different structures. Many bacteria produced these molecules as a part of their metabolism, especially those of the genus ''Bacillus'', ' ...
'' is a peptide that has a
lipid Lipids are a broad group of naturally-occurring molecules which includes fats, waxes, sterols, fat-soluble vitamins (such as vitamins A, D, E and K), monoglycerides, diglycerides, phospholipids, and others. The functions of lipids includ ...
connected to it, and '' pepducins'' are lipopeptides that interact with GPCRs. * A ''
peptide hormone Peptide hormones or protein hormones are hormones whose molecules are peptide, or proteins, respectively. The latter have longer amino acid chain lengths than the former. These hormones have an effect on the endocrine system of animals, including h ...
'' is a peptide that acts as a
hormone A hormone (from the Greek participle , "setting in motion") is a class of signaling molecules in multicellular organisms that are sent to distant organs by complex biological processes to regulate physiology and behavior. Hormones are require ...
. * A proteose is a mixture of peptides produced by the hydrolysis of proteins. The term is somewhat archaic. * A peptidergic agent (or drug) is a chemical which functions to directly modulate the peptide systems in the body or brain. An example is
opioidergic An opioidergic agent (or drug) is a chemical which functions to directly modulate the opioid neuropeptide systems (i.e., endorphin, enkephalin, dynorphin, nociceptin) in the body or brain. Examples include opioid analgesics such as morphine a ...
s, which are neuropeptidergics. * A cell-penetrating peptide is a peptide able to penetrate the cell membrane.


See also

* Acetyl hexapeptide-3 * Beefy meaty peptide * Collagen hybridizing peptide, a short peptide that can bind to denatured collagen in tissues * Bis-peptide *
CLE peptide CLE peptides (CLAVATA3/Embryo Surrounding Region-Related) are a group of peptides found in plants that are involved with cell signaling. Production is controlled by the CLE genes. Upon binding to a CLE peptide receptor in another cell, a chain react ...
* Epidermal growth factor * ''
Journal of Peptide Science The ''Journal of Peptide Science'' is a monthly peer-reviewed scientific journal, published since 1995 by John Wiley & Sons on behalf of the European Peptide Society. The current editor-in-chief is Paolo Rovero ( Universita di Firenze). Abstract ...
'' * Lactotripeptides *
Micropeptide Micropeptides (also referred to as microproteins) are polypeptides with a length of less than 100-150 amino acids that are encoded by short open reading frames (sORFs). In this respect, they differ from many other active small polypeptides, which ...
*
Multifunctional peptide A multifunctional peptide is a peptide which occurs when two genes band together. This process gives new properties to the polypeptide Peptides (, ) are short chains of amino acids linked by peptide bonds. Long chains of amino acids are called ...
* Neuropeptide * Palmitoyl pentapeptide-4 * Pancreatic hormone * peptide spectral library *
Peptide synthesis In organic chemistry, peptide synthesis is the production of peptides, compounds where multiple amino acids are linked via amide bonds, also known as peptide bonds. Peptides are chemically synthesized by the condensation reaction of the carboxyl ...
*
Peptidomimetic A peptidomimetic is a small protein-like chain designed to mimic a peptide. They typically arise either from modification of an existing peptide, or by designing similar systems that mimic peptides, such as peptoids and β-peptides. Irrespective ...
s (such as peptoids and β-peptides) to peptides, but with different properties. *
Protein tag Protein tags are peptide sequences genetically grafted onto a recombinant protein. Tags are attached to proteins for various purposes. They can be added to either end of the target protein, so they are either C-terminus or N-terminus specific or a ...
, describing addition of peptide sequences to enable protein isolation or detection * Replikins * Ribosome * Translation (biology)


References

{{Authority control Peptides