Post-translational modifications can occur on the amino acidside chains or at the protein's C- or N- termini.[1] They can expand the chemical set of the 22 amino acids by changing an existing functional group or adding a new one such as phosphate. Phosphorylation is highly effective for controlling the enzyme activity and is the most common change after translation. [2] Many eukaryotic and prokaryotic proteins also have carbohydrate molecules attached to them in a process called glycosylation, which can promote protein folding and improve stability as well as serving regulatory functions. Attachment of lipid molecules, known as lipidation, often targets a protein or part of a protein attached to the cell membrane.
Other forms of post-translational modification consist of cleaving peptide bonds, as in processing a propeptide to a mature form or removing the initiator methionine residue. The formation of disulfide bonds from cysteine residues may also be referred to as a post-translational modification.[3] For instance, the peptide hormoneinsulin 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.
Some types of post-translational modification are consequences of oxidative stress. Carbonylation is one example that targets the modified protein for degradation and can result in the formation of protein aggregates.[4][5] Specific amino acid modifications can be used as biomarkers indicating oxidative damage.[6]
In 2011, statistics of each post-translational modification experimentally and putatively detected have been compiled using proteome-wide information from the Swiss-Prot database.[24] The 10 most common experimentally found modifications were as follows:[25]
[27] – A database of comprehensive information and tools for the study of mammalian protein post-translational modification
PhosphoSitePlus
[28] – A database of proteins and post-translational modifications experimentally
ProteomeScout
[28] – A database for different modifications and understand different proteins, their class, and function/process related to disease causing proteins
Human Protein Reference Database
[29] – A database of Consensus patterns for many types of PTM's including sites
PROSITE
[30] – A database consisting of a collection of annotations and structures for PTMs.
RESID
[31]– A database that integrates PTM information from several knowledgbases and text mining results.
iPTMnet
[26] – A database that shows different PTM's and information regarding their chemical components/structures and a frequency for amino acid modified site
dbPTM
has PTM information although that may be less comprehensive than in more specialized databases.
Effect of PTMs on protein function and physiological processes.[32]
Uniprot
[33][34] - A curated database for protein O-GlcNAcylation and referencing more than 14 000 protein entries and 10 000 O-GlcNAc sites.
The O-GlcNAc Database
Cleavage and formation of during the production of insulin
