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Posttranslational modification
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Posttranslational modification

Posttranslational modification (PTM) is the chemical modification of a protein after its translation. It is one of the later steps in protein biosynthesis, and thus gene expression, for many proteins.

The bottom of this diagram shows the modification of primary structure of insulin, as described.
The bottom of this diagram shows the modification of primary structure of insulin, as described.
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.

Post-translational modification of proteins is detected by mass spectrometry or Eastern blotting.

Contents


PTMs involving addition of functional groups

The genetic code diagramGramatikoff K. in Abgent Catalog (2004-5) p.263 showing the amino acid residues as target of modification.
The genetic code diagram[1] showing the amino acid residues as target of modification.

PTMs involving addition by an enzyme in vivo

PTMs involving addition of hydrophobic groups for membrane localization

PTMs involving addition of cofactors for enhanced enzymatic activity

PTMs involving unique modifications of translation factors

PTMs involving addition of smaller chemical groups

PTMs involving non-enzymatic additions in vivo

  • glycation, the addition of a sugar molecule to a protein without the controlling action of an enzyme.

PTMs involving non-enzymatic additions in vitro

PTMs involving addition of other proteins or peptides

PTMs involving changing the chemical nature of amino acids

PTMs involving structural changes

Post-translational modification statistics

Recently statistics of each post-translational modification experimentally and putatively detected have been compiled using proteome-wide information from the Swiss-Prot database.[13] These statistics can be found at http://selene.princeton.edu/PTMCuration/.

Case examples

External links

References

ca:Modificaci postraduccional cs:Posttransla n modifikace da:Posttranslationel modifikation de:Posttranslationale Modifikation es:Modificaci n postraduccional fa: fr:Modification post-traductionnelle it:Modificazione post traduzionale nl:Posttranslationele modificatie ja: pl:Modyfikacje posttranslacyjne pt:Modifica o p s-traducional ru: sr:Posttranslaciona modifikacija tr: evrim sonras de i im uk: zh:






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