E3 SUMO-protein ligase; has a preference for SUMO2 and SUMO3 and facilitates UBE2I/UBC9-mediated sumoylation of target proteins. Plays a role in protein SUMO2 modification in response to stress caused by DNA damage and by proteasome inhibitors (in vitro). Required for MCM4 sumoylation. Has no activity with SUMO1 (PubMed:26524493). Preferentially transfers an additional SUMO2 chain onto the SUMO2 consensus site 'Lys-11'. Negatively regulates transcriptional activation mediated by the SMAD4 complex in response to TGF-beta signaling. Inhibits EP300-mediated acetylation of histone H3 at 'Lys-9'. Plays a role in regulating the transcription of AR targets (By similarity). Protein modification; protein sumoylation. Homooligomer. Interacts (via N-terminal region) with SUMO1. Interacts (via N-terminal region) with SUMO2. Interacts simultaneously with two SUMO2 chains. Identified in a complex with SUMO2 and UBE2I/UBC9, where one ZNF451 interacts with one UBE2I/UBC9 and two SUMO2 chains, one bound to the UBE2I/UBC9 active site and the other to another region of the same UBE2I/UBC9 molecule. Interacts (via C-terminus) with ubiquitin. Interacts (via N-terminal zinc-finger domains) with SMAD4 (via MH2 domain). Interacts with SMAD2 and SMAD3. Identified in a complex that contains at least ZNF451, SMAD2, SMAD3 and SMAD4. Interacts with EP300. Inhibits interaction between EP300 and the SMAD4 complex. Colocalizes with UBE2I/UBC9, SUMO1 and SUMO2 in nuclear granules; this probably requires sumoylation. Desumoylation leads to diffuse nucleoplasmic location. 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. Sumoylated. Predominantly sumoylated on the N-terminal region that is important for interaction with SUMO1 and SUMO2. Sumoylation is important for localization in nuclear granules; desumoylation leads to diffuse nucleoplasmic location. Autosumoylated (in vitro). Sumoylation enhances E3 SUMO-protein ligase activity. Belongs to the krueppel C2H2-type zinc-finger protein family.