The polypeptide chain made up of several amino acid residues gets released at the end of the translation process and undergoes appropriate folding to attain its secondary and tertiary structures. If the protein is made up of multiple subunits, these come together to form the native protein structure. Many proteins undergo chemical modifications at some of their amino acid residues after translation. These are carried out by enzyme-catalyzed reactions and are essential for normal functioning of the protein. The protein that has undergone the required PTMs and is ready to function is the modified protein in its native, stable state conformation.

Some of the most commonly observed PTMs include:

a) Phosphorylation: The addition of a phosphate group, usually to serine, threonine or tyrosine residues of the protein. Protein phosphorylation and dephosphorylation is one of the most important control mechanisms for the inter-conversion of proteins between their functional and non-functional states.

b) Glycosylation: The enzymatic addition of saccharides to specific amino acid residues resulting in the formation of glycoproteins. Sugars like glucose and mannose are commonly added to either nitrogen atoms of aspargine, arginine or to hydroxyl oxygen atoms of serine, threonine, tyrosine etc.

c) Methylation: Addition of a methyl group, usually at lysine or arginine residues.

d) Hydroxylation: Addition of a hydroxyl (-OH) group by the hydroxylase enzymes. Proline is usually the principal residue that is hydroxylated resulting in hydroxyproline, an essential and abundant component of connective tissues like collagen.

The protein obtained by translation undergoes folding and various PTMs such as phosphorylation, alkylation, glycosylation, hydroxylation etc. to give the final functional protein. This adds to the complexity of each protein since the functional protein product does not directly correspond to its gene sequence.