E2 Ubiquitin Enzymes
Ubiquitin-conjugating enzymes, also known as E2 enzymes and more rarely as
ubiquitin-carrier enzymes, perform the second step in the ubiquitination reaction
that targets a protein for degradation via the proteasome. E2 enzymes have a variety
of individual and redundant roles in cells and play important roles in target
degradation (proteasome pathway) and target modification (non-proteasome
pathway) for regulatory purposes. Ub/UBL conjugation is initiated by ATP-dependent
E1 enzyme and then transferred to cysteine, the active site of E2 enzyme.
Relationship with other enzymes
Ubiquitin-activating enzymes activate ubiquitin by covalently attaching molecules to
cysteine residues at their active sites. The activated protein is then transferred to E2
cysteine. Once bound to ubiquitin, E2 molecules bind to one of several ubiquitin
ligases or E3 proteins via a structurally conserved binding region. The E3 molecule
binds to the target protein substrate and transfers the lysine residues that pervade
the protein from E2 cysteine to the target protein.
