E3 SUMO-protein ligase; facilitates UBE2I/UBC9-mediated SUMO2 modification of target proteins (PubMed:26524493). Protein modification; protein sumoylation. Interacts with UBE2I/UBC9 and SUMO2. Binds UBE2I/UBC9 and two SUMO2 molecules via its N-terminus. The most N-terminal region interacts with the SUMO2 chain that is covalently bound to the UBE2I/UBC9 active site, while the second region interacts with another SUMO2 that is non-covalently associated with the same UBE2I/UBC9 chain.