Otubain 1 (OTUB1)

Otubain-1 is a member of the OTU (ovarian tumor) superfamily of predicted cysteine proteases. The encoded protein is a highly specific ubiquitin iso-peptidase, and cleaves ubiquitin from branched poly-ubiquitin chains, being specific for lysine⁴⁸ -linked polyubiquitin but not lysine⁶³ -linked polyubiquitin. It interacts with another ubiquitin protease and an E3 ubiquitin ligase that inhibits cytokine gene transcription in the immune system.

The 271-amino acid, 31-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 OTB1, with 2 isoforms in leukocytes.