Josephin family represents DUBs with a papain-like cysteine protease catalytic domain. As a well studied Josephin family protein of Ataxin-3, the structure of the Josephin domain was solved by NMR which resembles that of UCH domain deubiquitinating enzymes. Furthermore, the active site residues of Ataxin-3 are positioned in a catalytically competent conformation which has been reported to edit K63-linked chains specifically (1).

1. Reyes-Turcu, F.E., Ventii, K.H. and Wilkinson, K.D. (2009) Regulation and cellular roles of ubiquitin-specific deubiquitinating enzymes. Annu. Rev. Biochem., 78, 363-397. PMID: 19489724