This is a predicted metallopeptidase domain called WLM (Wss1p-like metalloproteases). These are linked to the Ub-system by virtue of fusions with the UB-binding PUG (PUB), Ub-like, and Little Finger domains. More specifically, genetic evidence implicates the WLM family in de-SUMOylation [1].

1: Novel predicted peptidases with a potential role in the ubiquitin signaling pathway. Iyer LM, Koonin EV, Aravind L; Cell Cycle 2004;3:1440-1450. PMID:15483401