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Peptides (from the Greek πεπτίδια, "small digestibles") are short polymers formed from the linking, in a defined order, of α-amino acids. Greek (el ελληνική γλώσσα or simply el ελληνικά — "Hellenic" is an Indo-European language, spoken today by 15-22 million people mainly A polymer is a large Molecule ( Macromolecule) composed of repeating Structural units typically connected by Covalent Chemical bonds In Chemistry, an amino acid is a Molecule containing both Amine and Carboxyl Functional groups In Biochemistry, this The link between one amino acid residue and the next is known as an amide bond or a peptide bond. In Chemistry, an amide is one of three kinds of Compounds (sometimes called acid amide the organic Functional group characterized A chemical bond is the physical process responsible for the attractive interactions between Atoms and Molecules and which confers stability to diatomic and polyatomic A peptide bond is a Chemical bond formed between two Molecules when the Carboxyl group of one molecule reacts with the

Proteins are polypeptide molecules (or consist of multiple polypeptide subunits). Proteins are large Organic compounds made of Amino acids arranged in a linear chain and joined together by Peptide bonds between the Carboxyl In Chemistry, a molecule is defined as a sufficiently stable electrically neutral group of at least two Atoms in a definite arrangement held together by 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.

Contents

Conventions

One convention is that those peptide chains that are short enough to be made synthetically from the constituent amino acids are called peptides rather than proteins. In Chemistry, an amino acid is a Molecule containing both Amine and Carboxyl Functional groups In Biochemistry, this However, with the advent of better synthetic techniques, peptides as long as hundreds of amino acids can be made, including full proteins like ubiquitin. Ubiquitin is a highly-conserved regulatory Protein that is ''ubiquitously'' expressed in Eukaryotes. Native chemical ligation has given access to even longer proteins, so this convention seems to be outdated. Native chemical ligation is the most widely used form of Chemical ligation, a technique for constructing a large Polypeptide from two or more unprotected peptides

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 peptide linked to Alzheimer's disease, can be considered proteins; and small proteins, such as insulin, can be considered peptides. Alzheimer's disease ( AD) also called Alzheimer disease or simply Alzheimer's, is the most common form of Dementia. Insulin is a Hormone with intensive effects on both metabolism and several other body systems (eg vascular compliance

Peptide classes

Here are the major classes of peptides, according to how they are produced:

Ribosomal peptides 
Are synthesized by translation of mRNA. Translation is the first stage of Protein biosynthesis (part of the overall process of Gene expression) Messenger ribonucleic acid ( mRNA) is a molecule of RNA encoding a chemical "blueprint" for a Protein product They are often subjected to proteolysis to generate the mature form. Proteolysis is the directed degradation ( digestion) of Proteins by cellular Enzymes called Proteases or by intramolecular digestion These function, typically in higher organisms, as hormones and signaling molecules. Hormones (from Greek ὁρμή - "impetus" are chemicals released by cells that affect cells in other parts of the body Some organisms produce peptides as antibiotics, such as microcins. In modern usage an antibiotic is a Chemotherapeutic agent with activity against Microorganisms such as Bacteria, fungi or Protozoa Microcins are very small Bacteriocins composed of a relatively few Peptides For this reason they are distinct from their larger Protein cousins [1] Since they are translated, the amino acid residues involved are restricted to those utilized by the ribosome. In Chemistry, an amino acid is a Molecule containing both Amine and Carboxyl Functional groups In Biochemistry, this However, these peptides frequently have posttranslational modifications, such as phosphorylation, hydroxylation, sulfonation, palmitylation, glycosylation and disulfide formation. Posttranslational modification (PTM is the chemical modification of a Protein after its translation. Phosphorylation is the addition of a Phosphate (PO4 group to a Protein molecule or a small molecule Hydroxylation is any chemical process that introduces one or more hydroxyl groups (-OH into a compound (or radical thereby oxidizing it Sulfonic acid is an unstable Acid with the formula H-S(=O2-OH In Chemistry, a disulfide bond is a single Covalent bond derived from the coupling of Thiol groups In general, they are linear, although lariat structures have been observed. Reata redirects here For the comic book character see Reata (comics A lasso, lariat, or riata (from the Spanish reata [2] More exotic manipulations do occur, such as racemization of L-amino acids to D-amino acids in platypus venom. The Platypus ( Ornithorhynchus anatinus) is a semi- aquatic Mammal endemic to eastern Australia, including Tasmania. This article is about the class of Biotoxins For other uses see Venom (disambiguation and Venomous (disambiguation. [3]
Nonribosomal peptides 
These peptides are assembled by enzymes that are specific to each peptide, rather than by the ribosome. Nonribosomal peptide s (NRP are a class of Peptide Secondary metabolites, usually produced by Microorganisms like bacteria and Fungi The most common non-ribosomal peptide is glutathione, which is a component of the antioxidant defenses of most aerobic organisms. Glutathione ( GSH) is a Tripeptide. It contains an unusual Peptide linkage between the amine group of Cysteine and the Carboxyl An antioxidant is a Molecule capable of slowing or preventing the oxidation of other molecules [4] Other nonribosomal peptides are most common in unicellular organisms, plants, and fungi and are synthesized by modular enzyme complexes called nonribosomal peptide synthetases. A microorganism (also spelled micro organism or micro-organism and also called a microbe) is an Organism that is Microscopic (usually Plants are living Organisms belonging to the kingdom Plantae. A fungus (ˈfʌŋgəs is a eukaryotic Organism that is a member of the kingdom Fungi (ˈfʌndʒaɪ Many organisms consist of modules, both anatomically and in their Metabolism. [5] 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. [6] These peptides are often cyclic and can have highly-complex cyclic structures, although linear nonribosomal peptides are also common. In Organic chemistry, a cyclic compound is a compound in which a series of carbon atoms are connected to form a loop or ring Since the system is closely related to the machinery for building fatty acids and polyketides, hybrid compounds are often found. In Chemistry, especially Biochemistry, a fatty acid is a Carboxylic acid often with a long unbranched Aliphatic tail ( chain) which Polyketides are Secondary metabolites from bacteria, Fungi, Plants and Animals Polyketides are biosynthesized by the Oxazoles, thiazoles often indicate that the compound was synthesized in this fashion. Oxazole is the parent compound for a vast class of heterocyclic Aromatic Organic compounds Thse are Azoles with an oxygen and a nitrogen Thiazole, or 13-thiazole, is a clear to pale yellow flammable liquid with a Pyridine -like odor and the molecular formula C3H3NS [7]
Peptones
See also Tryptone
Are derived from animal milk or meat digested by proteolytic digestion. Tryptone is a Peptide formed by the digestion of Casein (commonly found in milk by the Protease Trypsin. 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. [8]
Peptide Fragments 
Refer to fragments of proteins which used to identify or quantify the source protein. [9] 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. [10][11]

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. Proteins are large Organic compounds made of Amino acids arranged in a linear chain and joined together by Peptide bonds between the Carboxyl [12] 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. Mass spectrometry is an analytical technique that identifies the chemical composition of a compound or sample based on the Mass-to-charge ratio of charged particles In this case the peptides are most often generated by in-gel digestion after electrophoretic separation of the proteins. The in-gel digestion is part of the sample preparation for the mass spectrometric identification of Proteins in course of proteomic analysis. Electrophoresis is the most well-known electrokinetic phenomenon.

Peptides have recently been used in the study of protein structure and function. Proteins are an important class of biological Macromolecules present in all biological organisms made up of such elements as Carbon, Hydrogen 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

Vasoactive intestinal peptides

Pancreatic polypeptide-related peptides

Opioid peptides

Calcitonin peptides

Notes on terminology

See also

References

  1. ^ Duquesne S, Destoumieux-Garzón D, Peduzzi J, Rebuffat S (2007). Bis-peptides are analogues of Peptides but consist of Bis-amino acids which bear two Carboxyl groups and two Amino groups The connection of specific In Organic chemistry, peptide synthesis is the production of Peptides which are Organic compounds in which multiple Amino acids are linked via Translation is the first stage of Protein biosynthesis (part of the overall process of Gene expression) Ribosomes ( from ribo nucleic acid and "Greek soma ( meaning body") are complexes of RNA and Protein that "Microcins, gene-encoded antibacterial peptides from enterobacteria". Natural product reports 24 (4): 708–34. doi:10.1039/b516237h. A digital object identifier ( DOI) is a permanent identifier given to an Electronic document. PMID 17653356.  
  2. ^ Pons M, Feliz M, Antònia Molins M, Giralt E (1991). "Conformational analysis of bacitracin A, a naturally occurring lariat". Biopolymers 31 (6): 605–12. doi:10.1002/bip.360310604. A digital object identifier ( DOI) is a permanent identifier given to an Electronic document. PMID 1932561.  
  3. ^ Torres AM, Menz I, Alewood PF, et al (2002). "D-Amino acid residue in the C-type natriuretic peptide from the venom of the mammal, Ornithorhynchus anatinus, the Australian platypus". FEBS Lett. 524 (1-3): 172–6. doi:10.1016/S0014-5793(02)03050-8. A digital object identifier ( DOI) is a permanent identifier given to an Electronic document. PMID 12135762.  
  4. ^ Meister A, Anderson M (1983). "Glutathione". Annu Rev Biochem 52: 711 – 60. doi:10.1146/annurev.bi.52.070183.003431. A digital object identifier ( DOI) is a permanent identifier given to an Electronic document. PMID 6137189.  
  5. ^ Hahn M, Stachelhaus T (2004). "Selective interaction between nonribosomal peptide synthetases is facilitated by short communication-mediating domains". Proc. Natl. Acad. Sci. U. S. A. 101 (44): 15585–90. doi:10.1073/pnas.0404932101. A digital object identifier ( DOI) is a permanent identifier given to an Electronic document. PMID 15498872.  
  6. ^ Finking R, Marahiel MA (2004). "Biosynthesis of nonribosomal peptides1". Annu. Rev. Microbiol. 58: 453–88. doi:10.1146/annurev.micro.58.030603.123615. A digital object identifier ( DOI) is a permanent identifier given to an Electronic document. PMID 15487945.  
  7. ^ Du L, Shen B (2001). "Biosynthesis of hybrid peptide-polyketide natural products". Current opinion in drug discovery & development 4 (2): 215–28. PMID 11378961.  
  8. ^ Payne JW (1976). "Peptides and micro-organisms". Adv. Microb. Physiol. 13: 55–113. PMID 775944.  
  9. ^ Hummel J, Niemann M, Wienkoop S, et al (2007). "ProMEX: a mass spectral reference database for proteins and protein phosphorylation sites". BMC Bioinformatics 8: 216. doi:10.1186/1471-2105-8-216. A digital object identifier ( DOI) is a permanent identifier given to an Electronic document. PMID 17587460.  
  10. ^ Webster J, Oxley D (2005). "Peptide mass fingerprinting: protein identification using MALDI-TOF mass spectrometry". Methods Mol. Biol. 310: 227–40. PMID 16350956.  
  11. ^ Marquet P, Lachâtre G (1999). "Liquid chromatography-mass spectrometry: potential in forensic and clinical toxicology". J. Chromatogr. B Biomed. Sci. Appl. 733 (1-2): 93–118. doi:10.1016/S0378-4347(99)00147-4. A digital object identifier ( DOI) is a permanent identifier given to an Electronic document. PMID 10572976.  
  12. ^ Bulinski JC (1986). "Peptide antibodies: new tools for cell biology". Int. Rev. Cytol. 103: 281–302. PMID 2427468.  


Dictionary

peptide

-noun

  1. (biochemistry) A class of organic compounds consisting of various numbers of amino acids in which the amine of one is reacted with the carboxylic acid of the next to form an amide bond.
  2. (biochemistry) The peptide bond itself.
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