Ubiquitin-like protein that can be covalently attached to proteins as a monomer or as a lysine-linked polymer. Covalent attachment via an isopeptide bond to its substrates requires prior activation by the E1 complex SAE1-SAE2 and linkage to the E2 enzyme UBE2I, and can be promoted by an E3 ligase such as PIAS1-4, RANBP2 or CBX4. This post-translational modification on lysine residues of proteins plays a crucial role in a number of cellular processes such as nuclear transport, DNA replication and repair, mitosis and signal transduction. Polymeric SUMO2 chains are also susceptible to polyubiquitination which functions as a signal for proteasomal degradation of modified proteins. Plays a role in the regulation of sumoylation status of SETX (By similarity). Interacts with SAE2 and UBE2I. Interacts with ZNF451. Identified in a complex with ZNF451 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. Covalently attached to a number of proteins. Interacts with PELP1. Interacts with USP25; the interaction sumoylates USP25. Interacts with SIMC1, CASP8AP2, RNF111 AND SOBP (via SIM domains). Interacts with MTA1. Interacts with HINT1 (PubMed:31088288). Interacts with GCNA (via SIM domains); this interaction allows the GCNA recruitment to DPCs sites (By similarity). Polymeric chains can be formed through Lys-11 cross-linking. Polymeric SUMO2 chains undergo 'Lys-6'-, 'Lys-11'-, 'Lys-48'- and 'Lys-63'-linked polyubiquitination by RNF4 (By similarity). Cleavage of precursor form by SENP1 or SENP2 is necessary for function. Monoubiquitinated N-terminally by UBE2W, which primes it for RNF4-dependent polyubiquitination by the UBE2V1-UBE2N heterodimer. Belongs to the ubiquitin family. SUMO subfamily.