Figure 1.

The SUMO conjugation pathway. SUMO is expressed as a precursor protein and processed by a SUMO protease (SENP). Mature SUMO is activated in an ATP-dependent manner by the SUMO activating enzyme (E1) and is transferred through a transesterification process to the unique SUMO conjugating enzyme (E2) Ubc9. SUMO is next conjugated to the target lysine of a substrate (consensus sequence ΨKXE/D). Conjugation, in some instances, is facilitated by a SUMO E3 ligase. The sumoylation pathway is reversible as specific proteases can remove and recycle SUMO from modified substrates.