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Posttranslational modification (PTM) is a step in protein biosynthesis. Proteins are created by ribosomes translating mRNA into polypeptide chains. These polypeptide chains undergo PTM, (such as folding, cutting and other processes), before becoming the mature protein product.
A protein (also called a polypeptide) is a chain of amino acids. During protein synthesis, 20 different amino acids can be incorporated to become a protein. After translation, the posttranslational modification of amino acids extends the range of functions of the protein by attaching it to other biochemical functional groups (such as acetate, phosphate, various lipids and carbohydrates), changing the chemical nature of an amino acid (e.g. citrullination), or making structural changes (e.g. formation of disulfide bridges).
Also, enzymes may remove amino acids from the amino end of the protein, or cut the peptide chain in the middle. For instance, the peptide hormone insulin is cut twice after disulfide bonds are formed, and a propeptide is removed from the middle of the chain; the resulting protein consists of two polypeptide chains connected by disulfide bonds. Also, most nascent polypeptides start with the amino acid methionine because the "start" codon on mRNA also codes for this amino acid. This amino acid is usually taken off during post-translational modification.
Other modifications, like phosphorylation, are part of common mechanisms for controlling the behavior of a protein, for instance activating or inactivating an enzyme.
PTMs involving addition of functional groups Edit
PTMs involving addition by an enzyme in vivoEdit
PTMs involving addition of hydrophobic groups for membrane localizationEdit
- myristoylation, attachment of myristate, a C14 saturated acid
- palmitoylation, attachment of palmitate, a C16 saturated acid
- isoprenylation or prenylation, the addition of an isoprenoid group (e.g. farnesol and geranylgeraniol)
- glypiation, glycosylphosphatidylinositol (GPI) anchor formation via an amide bond to C-terminal tail
PTMs involving addition of cofactors for enhanced enzymatic activityEdit
- lipoylation, attachment of a lipoate (C8) functional group
- flavin moiety (FMN or FAD) may be covalently attached
- heme C attachment via thioether bonds with cysteins
- phosphopantetheinylation, the addition of a 4'-phosphopantetheinyl moiety from coenzyme A, as in fatty acid, polyketide, non-ribosomal peptide and leucine biosynthesis
- retinylidene Schiff base formation
PTMs involving unique modifications of translation factorsEdit
- diphthamide formation (on a histidine found in eEF2)
- ethanolamine phosphoglycerol attachment (on glutamte found in eEF1α)
- hypusine formation (on conserved lysine of eIF5A (eukaryotic) and aIF5A (archeal))
PTMs involving addition of smaller chemical groupsEdit
- acylation, e.g. O-acylation (esters), N-acylation (amides), S-acylation (thioesters)
- alkylation, the addition of an alkyl group, e.g. methyl, ethyl
- amide bond formation
- amidation at C-terminus
- amino acid addition
- gamma-carboxylation dependent on Vitamin K
- glycosylation, the addition of a glycosyl group to either arginine, asparagine, cysteine, hydroxylysine, serine, threonine, tyrosine, or tryptophan resulting in a glycoprotein. Distinct from glycation, which is regarded as a nonenzymatic attachment of sugars.
- iodination (e.g. of thyroglobulin)
- nucleotide addition such as ADP-ribosylation
- phosphate ester (O-linked) or phosphoramidate (N-linked) formation
- pyroglutamate formation
- succinylation addition of a succinyl group to lysine
- sulfation, the addition of a sulfate group to a tyrosine.
- selenoylation (co-translational incorporation of selenium in selenoproteins)
PTMs involving non-enzymatic additions in vivoEdit
- glycation, the addition of a sugar molecule to a protein without the controlling action of an enzyme.
PTMs involving non-enzymatic additions in vitroEdit
PTMs involving addition of other proteins or peptides Edit
- ISGylation, the covalent linkage to the ISG15 protein (Interferon-Stimulated Gene 15)
- SUMOylation, the covalent linkage to the SUMO protein (Small Ubiquitin-related MOdifier)
- ubiquitination, the covalent linkage to the protein ubiquitin.
- Neddylation, the covalent linkage to Nedd
- Pupylation, the covalent linkage to the Prokaryotic ubiquitin-like protein
PTMs involving changing the chemical nature of amino acids Edit
- citrullination, or deimination, the conversion of arginine to citrulline
- deamidation, the conversion of glutamine to glutamic acid or asparagine to aspartic acid
- eliminylation, the conversion to an alkene by beta-elimination of phosphothreonine and phosphoserine, or dehydration of threonine and serine, as well as by decarboxylation of cysteine 
- carbamylation, the conversion of lysine to homocitrulline 
PTMs involving structural changes Edit
- disulfide bridges, the covalent linkage of two cysteine amino acids
- proteolytic cleavage, cleavage of a protein at a peptide bond
- racemization of proline by prolyl isomerase
Post-translational modification statistics Edit
Recently, statistics of each post-translational modification experimentally and putatively detected have been compiled using proteome-wide information from the Swiss-Prot database. These statistics can be found at http://selene.princeton.edu/PTMCuration/.
Case examples Edit
- Cleavage and formation of disulfide bridges during the production of insulin
- PTM of histones as regulation of transcription: RNA polymerase control by chromatin structure
- PTM of RNA polymerase II as regulation of transcription
- Cleavage of polypeptide chains as crucial for lectin specificity
- dbPTM - database of protein post-translational modifications
- List of posttranslational modifications in ExPASy
- Browse SCOP domains by PTM — from the dcGO database
- Statistics of each post-translational modification from the Swiss-Prot database
- AutoMotif Server - A Computational Protocol for Identification of Post-Translational Modifications in Protein Sequences
- AutoMotif Server Version 3.0
- Functional analyses for site-specific phosphorylation of a target protein in cells
- Detection of Post-Translational Modifications after high-accuracy MSMS
- ↑ Gramatikoff K. in Abgent Catalog (2004-5) p.263
- ↑ Whiteheart SW, Shenbagamurthi P, Chen L, et al. (1989). Murine elongation factor 1 alpha (EF-1 alpha) is posttranslationally modified by novel amide-linked ethanolamine-phosphoglycerol moieties. Addition of ethanolamine-phosphoglycerol to specific glutamic acid residues on EF-1 alpha.. J. Biol. Chem. 264 (24): 14334–41.
- ↑ Polevoda B, Sherman F (2003). N-terminal acetyltransferases and sequence requirements for N-terminal acetylation of eukaryotic proteins. J Mol Biol 325 (4): 595–622.
- ↑ Yang XJ, Seto E (2008). Lysine acetylation: codified crosstalk with other posttranslational modifications. Mol Cell 31 (4): 449–61.
- ↑ Bártová E, Krejcí J, Harnicarová A, Galiová G, Kozubek S (2008). Histone modifications and nuclear architecture: a review. J Histochem Cytochem 56 (8): 711–21.
- ↑ Glozak MA, Sengupta N, Zhang X, Seto E (2005). Acetylation and deacetylation of non-histone proteins. Gene 363: 15–23.
- ↑ Eddé B, Rossier J, Le Caer JP, Desbruyères E, Gros F, Denoulet P (1990). Posttranslational glutamylation of alpha-tubulin. Science 247 (4938): 83–5.
- ↑ Walker CS, Shetty RP, Clark K, et al. (2001). On a potential global role for vitamin K-dependent gamma-carboxylation in animal systems. Animals can experience subvaginalhemototitis as a result of this linkage. Evidence for a gamma-glutamyl carboxylase in Drosophila. J. Biol. Chem. 276 (11): 7769–74.
- ↑ Malakhova, Oxana A.; Yan, Ming; Malakhov, Michael P.; Yuan, Youzhong; Ritchie, Kenneth J.; Kim, Keun Il; Peterson, Luke F.; Shuai, Ke; and Dong-Er Zhang (2003). Protein ISGylation modulates the JAK-STAT signaling pathway. Genes & Development 17 (4): 455–60.
- ↑ Van G. Wilson (Ed.) (2004). Sumoylation: Molecular Biology and Biochemistry. Horizon Bioscience. ISBN 0-9545232-8-8.
- ↑ Brennan DF, Barford D (2009). Eliminylation: a post-translational modification catalyzed by phosphothreonine lyases. Trends in Biochemical Sciences 34 (3): 108–114.
- ↑ Mydel P, et al. (2010). Carbamylation-dependent activation of T cells: a novel mechanism in the pathogenesis of autoimmune arthritis.. Journal of Immunology 184 (12): 6882–6890.
- ↑ Khoury, George A.; Baliban, Richard C.; and Christodoulos A. Floudas (2011). Proteome-wide post-translational modification statistics: frequency analysis and curation of the swiss-prot database. Scientific Reports 1 (90).
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