Peptide 24029 224266649 2008-07-08T02:00:33Z 66.123.206.45 Fix typo. /* Peptide classes */ '''Peptides''' (from the [[Greek language|Greek]] ''πεπτίδια'', "small digestibles") are short [[polymer]]s formed from the linking, in a defined order, of α-[[amino acid]]s. The link between one amino acid residue and the next is known as an [[amide]] [[chemical bond|bond]] or a [[peptide bond]]. [[Protein]]s are '''polypeptide''' [[molecule]]s (or consist of multiple polypeptide subunits). The distinction is that peptides are short and polypeptides/proteins are long. There are several different conventions to determine these, all of which have caveats and nuances. ==Conventions== One convention is that those peptide chains that are short enough to be made synthetically from the constituent [[amino acid]]s are called peptides rather than proteins. However, with the advent of better synthetic techniques, peptides as long as hundreds of amino acids can be made, including full proteins like [[ubiquitin]]. [[Native chemical ligation]] has given access to even longer proteins, so this convention seems to be outdated. Another convention places an informal dividing line at approximately 50 amino acids in length (some people claim shorter lengths). However, this definition is somewhat arbitrary. Long peptides, such as the [[amyloid beta|amyloid beta peptide]] linked to [[Alzheimer's disease]], can be considered proteins; and small proteins, such as [[insulin]], can be considered peptides. ==Peptide classes== Here are the major classes of peptides, according to how they are produced: ; Ribosomal peptides : Are synthesized by [[Translation (biology)|translation]] of [[mRNA]]. They are often subjected to [[proteolysis]] to generate the mature form. These function, typically in higher organisms, as [[hormone]]s and signaling molecules. Some organisms produce peptides as [[antibiotic]]s, such as [[microcins]].<ref>{{cite journal |author=Duquesne S, Destoumieux-Garzón D, Peduzzi J, Rebuffat S |title=Microcins, gene-encoded antibacterial peptides from enterobacteria |journal=Natural product reports |volume=24 |issue=4 |pages=708–34 |year=2007 |pmid=17653356 | doi = 10.1039/b516237h <!--Retrieved from CrossRef by DOI bot-->}}</ref> Since they are translated, the [[amino acid residue]]s involved are restricted to those utilized by the ribosome. However, these peptides frequently have [[posttranslational modification]]s, such as [[phosphorylation]], [[hydroxylation]], [[sulfonation]], palmitylation, glycosylation and [[disulfide bridge|disulfide]] formation. In general, they are linear, although [[lariat]] structures have been observed.<ref>{{cite journal |author=Pons M, Feliz M, Antònia Molins M, Giralt E |title=Conformational analysis of bacitracin A, a naturally occurring lariat |journal=Biopolymers |volume=31 |issue=6 |pages=605–12 |year=1991 |pmid=1932561 | doi = 10.1002/bip.360310604 <!--Retrieved from CrossRef by DOI bot-->}}</ref> More exotic manipulations do occur, such as racemization of L-amino acids to D-amino acids in [[platypus]] [[venom]].<ref>{{cite journal |author=Torres AM, Menz I, Alewood PF, ''et al'' |title=D-Amino acid residue in the C-type natriuretic peptide from the venom of the mammal, Ornithorhynchus anatinus, the Australian platypus |journal=FEBS Lett. |volume=524 |issue=1-3 |pages=172–6 |year=2002 |pmid=12135762 | doi = 10.1016/S0014-5793(02)03050-8 <!--Retrieved from CrossRef by DOI bot-->}}</ref> ; [[Nonribosomal peptide]]s : These peptides are assembled by enzymes that are specific to each peptide, rather than by the ribosome. The most common non-ribosomal peptide is [[glutathione]], which is a component of the [[antioxidant]] defenses of most aerobic organisms.<ref name=MeisterB>{{cite journal |author=Meister A, Anderson M |title=Glutathione |journal=Annu Rev Biochem |volume=52 |pages=711 – 60 |year=1983 |pmid=6137189 | doi = 10.1146/annurev.bi.52.070183.003431 <!--Retrieved from CrossRef by DOI bot-->}}</ref> Other nonribosomal peptides are most common in [[unicellular organism]]s, [[plant]]s, and [[fungi]] and are synthesized by [[Modularity (biology)|modular]] enzyme complexes called ''nonribosomal peptide synthetases''.<ref>{{cite journal |author=Hahn M, Stachelhaus T |title=Selective interaction between nonribosomal peptide synthetases is facilitated by short communication-mediating domains |journal=Proc. Natl. Acad. Sci. U.S.A. |volume=101 |issue=44 |pages=15585–90 |year=2004 |pmid=15498872 |url=http://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pubmed&pubmedid=15498872 | doi = 10.1073/pnas.0404932101 <!--Retrieved from CrossRef by DOI bot-->}}</ref> 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.<ref>{{cite journal |author=Finking R, Marahiel MA |title=Biosynthesis of nonribosomal peptides1 |journal=Annu. Rev. Microbiol. |volume=58 |pages=453–88 |year=2004 |pmid=15487945 | doi = 10.1146/annurev.micro.58.030603.123615 <!--Retrieved from CrossRef by DOI bot-->}}</ref> These peptides are often [[Cyclic compound|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 acid]]s and [[polyketide]]s, hybrid compounds are often found. [[Oxazoles]], [[thiazoles]] often indicate that the compound was synthesized in this fashion.<ref>{{cite journal |author=Du L, Shen B |title=Biosynthesis of hybrid peptide-polyketide natural products |journal=Current opinion in drug discovery & development |volume=4 |issue=2 |pages=215–28 |year=2001 |pmid=11378961}}</ref> ; Peptones :: ''See also [[Tryptone]]'' : Are derived from animal milk or meat digested by proteolytic digestion. In addition to containing small peptides, the resulting spray-dried material includes fats, metals, salts, vitamins and many other biological compounds. Peptone is used in nutrient media for growing bacteria and fungi.<ref>{{cite journal |author=Payne JW |title=Peptides and micro-organisms |journal=Adv. Microb. Physiol. |volume=13 |issue= |pages=55–113 |year=1976 |pmid=775944}}</ref> ; Peptide Fragments : Refer to fragments of proteins that are used to identify or quantify the source protein.<ref>{{cite journal |author=Hummel J, Niemann M, Wienkoop S, ''et al'' |title=ProMEX: a mass spectral reference database for proteins and protein phosphorylation sites |journal=BMC Bioinformatics |volume=8 |issue= |pages=216 |year=2007 |pmid=17587460 |url=http://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pubmed&pubmedid=17587460 | doi = 10.1186/1471-2105-8-216 <!--Retrieved from CrossRef by DOI bot-->}}</ref> Often these are the products of enzymatic degradation performed in the laboratory on a controlled sample, but can also be forensic or paleontological samples which have been degraded by natural effects.<ref>{{cite journal |author=Webster J, Oxley D |title=Peptide mass fingerprinting: protein identification using MALDI-TOF mass spectrometry |journal=Methods Mol. Biol. |volume=310 |issue= |pages=227–40 |year=2005 |pmid=16350956}}</ref><ref>{{cite journal |author=Marquet P, Lachâtre G |title=Liquid chromatography-mass spectrometry: potential in forensic and clinical toxicology |journal=J. Chromatogr. B Biomed. Sci. Appl. |volume=733 |issue=1-2 |pages=93–118 |year=1999 |pmid=10572976 | doi = 10.1016/S0378-4347(99)00147-4 <!--Retrieved from CrossRef by DOI bot-->}}</ref> == Peptides in molecular biology == Peptides have received prominence in molecular biology in recent times for several reasons. The first and most important is that peptides allow the creation of ''peptide antibodies'' in animals without the need to purify the [[protein]] of interest.<ref>{{cite journal |author=Bulinski JC |title=Peptide antibodies: new tools for cell biology |journal=Int. Rev. Cytol. |volume=103 |pages=281–302 |year=1986 |pmid=2427468}}</ref> This involves synthesizing antigenic peptides of sections of the protein of interest. These will then be used to make antibodies in a rabbit or mouse against the protein. Another reason is that peptides have become instrumental in [[mass spectrometry]], allowing the identification of proteins of interest based on peptide masses and sequence. In this case the peptides are most often generated by [[in-gel digestion]] after [[electrophoresis|electrophoretic]] separation of the proteins. Peptides have recently been used in the study of [[Protein_structure|protein structure]] and function. For example, synthetic peptides can be used as probes to see where protein-peptide interactions occur. Inhibitory peptides are also used in clinical research to examine the effects of peptides on the inhibition of cancer proteins and other diseases. ==Well-known peptide families in humans== The peptide families in this section are all 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 signalling functions. ===The Tachykinin peptides=== * [[Substance P]] * [[Kassinin]] * [[Neurokinin A]] * [[Eledoisin]] * [[Neurokinin B]] ===Vasoactive intestinal peptides=== * [[Vasoactive intestinal peptide|VIP]] ''Vasoactive intestinal peptide'' * [[PACAP]] ''[[Pituitary adenylate cyclase activating peptide]]'' * [[PHI 27]] * [[PHM 27]] * [[GHRH 1-24]] ''[[Growth hormone releasing hormone 1-24]]'' * [[Glucagon]] * [[Secretin]] ===Pancreatic polypeptide-related peptides=== * [[NPY]] * [[PYY]] ''[[Peptide YY]]'' * [[Avian pancreatic polypeptide|APP]] ''[[Avian pancreatic polypeptide]]'' * [[HPP]] ''[[Human pancreatic polypeptide]]'' ===Opioid peptides=== * [[Proopiomelanocortin]] ([[POMC]]) Peptides * The [[Enkephalin]] pentapeptides * The [[Prodynorphin]] peptides ===Calcitonin peptides=== * [[Calcitonin]] * [[Amylin]] * [[AGG01]] ==Notes on terminology== *A ''polypeptide'' is a single linear chain of amino acids. *A ''[[protein]]'' is one or more polypeptides more than about 50 amino acids long. *An ''[[oligopeptide]]'' or (simply) a ''peptide'' is a polypeptide less than 30-50 amino acids long. *A ''[[dipeptide]]'' has two amino acids. *A ''[[tripeptide]]'' has three amino acids. *A ''pentapeptide'' has five amino acids. *A ''[[nonapeptide]]'' has nine amino acids (e.g., [[oxytocin]]). *A ''[[decapeptide]]'' has ten amino acids (e.g., [[gonadotrophin geleasing hormone]]). *A ''[[neuropeptide]]'' is a peptide that is active in association with neural tissue. *A ''[[peptide hormone]]'' is a peptide that acts as a [[hormone]]. ==See also== * [[Peptidomimetic]]s (such as [[peptoid]]s and [[beta-peptide|β-peptide]]s) to peptides, but with different properties. * [[bis-peptide]] * [[Peptide synthesis]] * [[Translation (genetics)|Translation]] * [[Ribosome]] * [[Argireline]] ==References== {{reflist}} {{Peptides}} [[Category:Peptides| ]] [[ar:هضميد]] [[bg:Полипептид]] [[ca:Pèptid]] [[cs:Peptid]] [[da:Peptid]] [[de:Peptid]] [[et:Peptiidid]] [[el:Πεπτίδιο]] [[es:Péptido]] [[eo:Peptido]] [[fa:پپتید]] [[fr:Peptide]] [[ko:펩타이드]] [[it:Peptide]] [[he:פפטיד]] [[lt:Polipeptidas]] [[mk:Пептид]] [[nl:Polypeptide]] [[ja:ペプチド]] [[no:Peptid]] [[nn:Peptid]] [[oc:Peptid]] [[pl:Peptydy]] [[pt:Peptídeo]] [[ru:Пептиды]] [[sq:Peptidet]] [[sk:Peptid]] [[fi:Peptidi]] [[sv:Peptid]] [[th:เปปไทด์]] [[tr:peptit]] [[uk:Пептиди]] [[ur:Peptide]] [[zh:肽]]