About Ubiquitin

Ubiquitin (Ub) is a small protein of 76 amino acids. It is arguably the most conserved protein in eukaryotes, with only three amino acid differences between yeast and human ubiquitin. It functions as a post-translational modification (PTM) via attachment to the ε-amine of a lysine residue in a substrate protein.

Ubiquitination, i.e., the attachment of Ub, is catalyzed by a cascade of enzymes named E1, E2 and E3. The number of genes that encode each class of enzyme in the human genome form a pyramid structure. Specific combinations of E2 and E3 enzymes determine substrate specificity as well as the type of polyUb chains that are formed.

Like other PTMs, ubiquitination is reversible. Removal of the (poly)Ub signal is carried out by Deubiquitinating enzymes (DUBs).