Otubain 2 (OTUB2) is a member of DUBs that belong to the ovarian tumour (OTU) superfamily of proteins which consists of a five-stranded β-sheet sandwiched in between a small helical amino-terminal region consisting of α1 and α2, and a large helical region comprised of α3-α1. Like other DUBs, otubain 2 (OTUB2) cleaves proteins precisely at the ubiquitin-protein bond so that ubiquitylation process can be reversed and regulated. Otubain 2 (OTUB2)'s active-site cleft is sterically occluded by a novel loop conformation resulting in an oxyanion hole, which consists uniquely of backbone amides. Furthermore, the residues that orient and stabilize the active-site histidine of otubain 2 (OTUB2) are different from other cysteine proteases. This reorganization of the active-site topology provides a possible explanation for the low turnover and substrate specificity of the otubains.