Ubiquitin Related Proteins

Ubiquitin (Ub) is a highly conserved small protein containing 76 amino acids that is ubiquitously expressed in eukaryotic cells. The covalent attachment of ubiquitin to target proteins, namely ubiquitination, is an important type of protein posttranslational modification (PTM). Ubiquitination plays a crucial role in controlling various proteins’ stability and functions, regulating many cellular pathways, such as cell division and differentiation, response to environmental stress, cell differentiation, immune response, DNA repair, and apoptosis. The ubiquitin-proteasome pathway (UPP), a well-known pathway, is the primary cytosolic proteolytic machinery for the selective degradation of various forms of damaged proteins. Ubiquitination occurs in a three-step reaction requiring three different enzymes: 1) Ubiquitin activation by an Ub -activating enzyme (E1); 2) Activated ubiquitin is transferred from E1 to a cysteinyl residue in an Ub-conjugating enzyme (E2); 3) Ubiquitin is ligated to the lysine residues of target proteins by an Ub-ligase enzyme (E3).