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Post-translational modification

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Postranslational modification is the chemical modification of a protein after its translation. It is one of the later steps in protein biosynthesis for many proteins.

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 in proteins. After translation, the posttranslational modification (PTM) of amino acids extends the range of functions of the protein by attaching to it other biochemical functional groups such as acetate, phosphate, various lipids and carbohydrates, by changing the chemical nature of an amino acid (e.g. citrullination) or by making structural changes, like the 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.

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

PTMs involving addition include:

PTMs involving addition of other proteins or peptides

PTMs involving changing the chemical nature of amino acids

PTMs involving structural changes

Case examples

References

1. Van G. Wilson (Ed.) (2004). Sumoylation: Molecular Biology and Biochemistry. Horizon Bioscience. ISBN 0-9545232-8-8.

2. 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), 455-460.

Protein primary structure and posttranslational modifications
General
N terminus
C terminus
Single specific AAs
Serine/Threonine
Tyrosine
Cysteine
Aspartate
Glutamate
Asparagine
Glutamine
Lysine
Arginine
Proline
Histidine
Tryptophan
Crosslinks between two AAs
CysteineCysteine
MethionineHydroxylysine
LysineTyrosine
TryptophanTryptophan
Crosslinks between three AAs
SerineTyrosineGlycine
HistidineTyrosineGlycine
AlanineSerineGlycine
Crosslinks between four AAs
AllysineAllysineAllysineLysine
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