3) Ubiquitinylation

Proteins are usually modified for selective destruction by cellular proteolytic complexes called proteasomes by attachment of ubiquitin . Ubiquitinylation involves attachment of a small 76 amino acid protein called ubiquitin to the polypeptide chain following which it is degraded by the cellular proteasome machinery. Ubiquitin binds to the lysine residue of the target protein, present in a specific sequence. The tagged protein is then recognized by the proteasomes complex and it gets degraded.

Apart from the above mentioned PTMs there are other types of PTMs as well which are −

a)  SUMOylation- SUMO (small ubiquitin related modifier) proteins are 100 amino acid residue proteins which bind to the target protein in same way as ubiquitin, except it also confers the transcription regulatory activity of the protein. It also helps in transport of the target protein from cytosol to the nucleus.

b)  Phosphorylation: Involved in Signal transduction, regulation of enzyme activity.

c)  Disulfide bond formation: Stabilizes protein structure and involved in redox processes.

d)  Lipidylation.

e) Sulfation: Signalling and protein localization; also involved in protein−protein interactions.

f)  Hydroxylation: Structural stability (collagens).

g)  Acetylation

h)  Methylation

i)  Prenylation and so on.