Otubains are deubiquitylating cysteine proteases (DUBs) that belong to the ovarian tumor (OTU) protein superfamily. Like other DUBs, otubains cleave proteins precisely at the ubiquitin (UB)-protein bond.

By affinity purification of DUBs from HeLa cells using UB aldehyde (UBAL), followed by SDS-PAGE and mass spectrophotometric analysis, Balakirev et al. (2003) obtained cDNAs encoding OTB1 and OTB2. The 234-amino acid, 27-kD OTB1 protein contains UB-interaction motifs (UIMs) and UB-associated (UBA) domains, as well as putative nuclear localization signals and a consensus LxxLL motif. RT-PCR and Western blot analyses revealed wide expression of OTB2, with highest expression in brain.