SAE1

SAE1, also known as Aos1 and encoded by the AOS1 gene, is the non-catalytic subunit of the SUMO-activating enzyme. It heterodimerizes with its catalytic partner SAE2 (UBA2) to form the single E1 dedicated to all SUMO paralogs. Structurally, SAE1 provides the adenylation-domain half of the complex and a helix-helix docking surface for the SUMO C-terminus, while the thioester-forming cysteine resides on SAE2. The SAE1/SAE2 heterodimer activates SUMO1, SUMO2, and SUMO3 through ATP-dependent adenylation and passes them to the E2 enzyme UBE2I. Because UBE2I is the only SUMO E2, SAE1 sits at the apex of every SUMOylation event, making the E1 a target for SUMO-pathway inhibitors.