Hydrolase that can remove conjugated ubiquitin from proteins in vitro and may therefore play an important regulatory role at the level of protein turnover by preventing degradation. Mediates deubiquitination of 'Lys-11'-,'Lys-48'- and 'Lys-63'-linked polyubiquitin chains, with a preference for 'Lys-63'-linked polyubiquitin chains. Thiol-dependent hydrolysis of ester, thioester, amide, peptide and isopeptide bonds formed by the C-terminal Gly of ubiquitin (a 76-residue protein attached to proteins as an intracellular targeting signal). Widely expressed. Expressed at higher level in brain. In the structure described by PubMed:15258613, the Asp-48 active site of the catalytic triad is located too far to interact directly with the active site His-224. A possible explanation is that OTUB2 is in inactive conformation in absence of ubiquitin and a conformation change may move Asp-48 in the proximity of His-224 in presence of ubiquitin substrate. Belongs to the peptidase C65 family.