SUMO enzymatic cascade catalyzes the dynamic posttranslational modification process of sumoylation (i.e. transfer of SUMO protein to other proteins). The Small Ubiquitin-related Modifier, SUMO-1, is a ubiquitin-like family member that is conjugated to its substrates through three discrete enzymatic steps (see the figure on the right): activation, involving the E1 enzyme (SAE1/SAE2); conjugation, involving the E2 enzyme (UBE2I); substrate modification, through the cooperation of the E2 and E3 protein ligases.