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 (Probable). Cysteine protease with a preference for 'Lys-63' over 'Lys-48' over 'Met-1' -linked ubiquitin (UB) tetramers as substrates (PubMed:24659992). Cleaves also RUB-GST fusion (PubMed:24659992). 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). Optimum pH is 7. Belongs to the peptidase C85 family.