Most proteins that are translated from mRNA undergo modifications before becoming functional in cells. These modifications are collectively known as post-translational modifications. The nascent or folded proteins, which are stable under physiological conditions, are then subjected to a battery of specific enzyme-catalyzed modifications on the side chains or backbones.
Post-translational modification of proteins can include acetylation, acylation (myristoylation, palmitoylation), alkylation, arginylation, ADP-ribosylation, biotinylation, formylation, geranylgeranylation, glutamylation, glycosylation, glycylation, hydroxylation, isoprenylation, lipoylation, methylation, nitroalkylation, phosphopantetheinylation, phosphorylation, prenylation, selenation, S-nitrosylation, succinylation, sulfation, transglutamination, sulfinylation, sulfonylation and ubiquitination (sumoylation, neddylation).
Post-translational modifications occurring at the N-terminus of the amino acid chain play an important role in translocation across biological membranes. These include secretory proteins in prokaryotes and eukaryotes and also proteins that are intended to be incorporated in various cellular and organelle membranes such as lysosomes, chloroplast, mitochondria and plasma membrane. Expression of posttranslated proteins is important in several diseases.