Post-translational modification (PTM) refers to chemical modification of amino acids after they have been incorporated into protein chains in sequences specified by the genome. Proteolysis of protein chains is another form of PTM. PTM affect the functions of proteins. More than 200 kinds of PTM are known, affecting 15 of the 20 standard amino acids.
- Phosphorylation, notably of tyrosine, serine, or threonine, effected by protein kinases.
- Dephosphorylation is accomplished by protein phosphatases.
- Glycosylation, notably of asparagine (N-linked glycosylation), serine, or threonine.
- Acylation: attachment of acyl carboxylic acids, most commonly acetic (C2), myristic (C14), and palmitic (C16) acids.
- Ubiquitin is attached to proteins by acylation, using its carboxy-terminal glycine to form an isopeptide bond with a lysine in the target protein.
- De-acylation is accomplished by de-acylases.
- Alkylation, notably methylation, S-prenylation, and adenylation.
- Oxidation, notably creating hydroxylated proline, lysine, asparagine, and glutamic acid, as well as sulfation or nitrosylation of tyrosine.
- C-terminal amidation, neutralizing the charge.
- ADP ribosylation, a common mechanism used by bacterial toxins.
- Disulfide bond formation.
Consequences for Function
PTM induce conformational changes in proteins, and affect oligomerization and ligand binding. PTM may affect catalysis by direct modification of catalytic residues, modification of nearby residues, or effects on regulation.
Consequences for Proteome
About 5% of the genome of eukaryotes is devoted to enzymes that carry out PTM. PTM may increase the number of unique proteins in an organism by more than an order of magnitude.
- ↑ 1.0 1.1 1.2 Kessel, Amit, and Ben-Tal, Nir. Introduction to proteins: structure, function, and motion. CRC Press, 2011.
- ↑ Walsh CT, Garneau-Tsodikova S, Gatto GJ Jr. Protein posttranslational modifications: the chemistry of proteome diversifications. Angew Chem Int Ed Engl. 2005 Dec 1;44(45):7342-72. PMID:16267872 doi:10.1002/anie.200501023