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 (PubMed:24659992). Cysteine protease with a preference for 'Lys-63' over 'Lys-48'-linked over 'Met-1' ubiquitin (UB) tetramers (e.g. Ub3 and Ub4) 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. Prediction of a peroxisomal location. Belongs to the peptidase C65 family.