Fig. 2

Ubiquitination/deubiquitination mechanisms. A Ubiquitination is a reversible three-step enzymatic process in which participate ubiquitin-activating (E1), ubiquitin-conjugating (E2), and ubiquitin ligase (E3) enzymes. Conjugated ubiquitins are removed from the target proteins by deubiquitinases (DUBs) (see text for full description). B Eight main types of ubiquitin chains with distinct cellular functions can be formed, depending on the ubiquitin lysine residue involved (K6, K11, K27, K29, K33, K48, or K63). Linear ubiquitin chains (M1) are formed by a head-to-tail linkage between the C-terminal carboxyl group of one ubiquitin and the N-terminal methionine of another ubiquitin molecule (see text for full description). A “U” inside a green circle depicts ubiquitin residues