Amino acids that have been incorporated into peptides are termedresidues. A water molecule is released during formation of eachamide bond.[6] All peptides exceptcyclic peptides have anN-terminal (amine group) andC-terminal (carboxyl group) residue at the end of the peptide (as shown for the tetrapeptide in the image).
There are numerous types of peptides that have been classified according to their sources and functions. According to theHandbook 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,opioid peptides,neurotrophic peptides, and blood–brain peptides.[7]
Some ribosomal peptides are subject toproteolysis. These function, typically in higher organisms, ashormones and signaling molecules. Some microbes produce peptides asantibiotics, such asmicrocins andbacteriocins.[8]
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.[13] These peptides are oftencyclic and can have highly complex cyclic structures, although linear nonribosomal peptides are also common. Since the system is closely related to the machinery for buildingfatty acids andpolyketides, hybrid compounds are often found. The presence ofoxazoles orthiazoles often indicates that the compound was synthesized in this fashion.[14]
Peptones are derived from animal milk or meat digested byproteolysis.[15] 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.[16]
Peptide fragments refer to fragments of proteins that are used to identify or quantify the source protein.[17] 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.[18][19]
Example of a protein (orange) and peptide (green) interaction. Obtained from Propedia: a peptide-protein interactions database.[20]
Peptides can perform interactions with proteins and other macromolecules. They are responsible for numerous important functions in human cells, such as cell signaling, and act as immune modulators.[21] Indeed, studies have reported that 15-40% of all protein-protein interactions in human cells are mediated by peptides.[22] Additionally, it is estimated that at least 10% of the pharmaceutical market is based on peptide products.[21]
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.[23]
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 usingIUPAC numerical multiplier prefixes:
Aproteose is a mixture of peptides produced by the hydrolysis of proteins. The term is somewhat archaic.
Apeptidergic agent (or drug) is a chemical which functions to directly modulate the peptide systems in the body or brain. An example isopioidergics, which areneuropeptidergics.
A cell-penetrating peptide is a peptide able to penetrate the cell membrane.
^Abba J. Kastin, ed. (2013).Handbook of Biologically Active Peptides (2nd ed.). Elsevier Science.ISBN978-0-12-385095-9.
^Duquesne S, Destoumieux-Garzón D, Peduzzi J, Rebuffat S (August 2007). "Microcins, gene-encoded antibacterial peptides from enterobacteria".Natural Product Reports.24 (4):708–34.doi:10.1039/b516237h.PMID17653356.
^Pons M, Feliz M, Antònia Molins M, Giralt E (May 1991). "Conformational analysis of bacitracin A, a naturally occurring lariat".Biopolymers.31 (6):605–12.doi:10.1002/bip.360310604.PMID1932561.S2CID10924338.
^Tao, Kai; Levin, Aviad; Adler-Abramovich, Lihi; Gazit, Ehud (26 Apr 2016). "Fmoc-modified amino acids and short peptides: simple bio-inspired building blocks for the fabrication of functional materials".Chem. Soc. Rev.45 (14):3935–3953.doi:10.1039/C5CS00889A.PMID27115033.
^Tao, Kai; Wang, Jiqian; Zhou, Peng; Wang, Chengdong; Xu, Hai; Zhao, Xiubo; Lu, Jian R. (February 10, 2011). "Self-Assembly of Short Aβ(16−22) Peptides: Effect of Terminal Capping and the Role of Electrostatic Interaction".Langmuir.27 (6):2723–2730.doi:10.1021/la1034273.PMID21309606.
^Kai Tao; Guy Jacoby; Luba Burlaka; Roy Beck; Ehud Gazit (July 26, 2016). "Design of Controllable Bio-Inspired Chiroptic Self-Assemblies".Biomacromolecules.17 (9):2937–2945.doi:10.1021/acs.biomac.6b00752.PMID27461453.
^Kai Tao; Aviad Levin; Guy Jacoby; Roy Beck; Ehud Gazit (23 August 2016). "Entropic Phase Transitions with Stable Twisted Intermediates of Bio-Inspired Self-Assembly".Chem. Eur. J.22 (43):15237–15241.doi:10.1002/chem.201603882.PMID27550381.
^Donghui Jia; Kai Tao; Jiqian Wang; Chengdong Wang; Xiubo Zhao; Mohammed Yaseen; Hai Xu; Guohe Que; John R. P. Webster; Jian R. Lu (June 16, 2011). "Dynamic Adsorption and Structure of Interfacial Bilayers Adsorbed from Lipopeptide Surfactants at the Hydrophilic Silicon/Water Interface: Effect of the Headgroup Length".Langmuir.27 (14):8798–8809.doi:10.1021/la105129m.PMID21675796.
^Xu JY, Qin LQ, Wang PY, Li W, Chang C (October 2008). "Effect of milk tripeptides on blood pressure: a meta-analysis of randomized controlled trials".Nutrition.24 (10):933–40.doi:10.1016/j.nut.2008.04.004.PMID18562172.
