Zinc metalloprotease that specifically cleaves 'Lys-63'-linked polyubiquitin chains. Does not cleave 'Lys-48'-linked polyubiquitin chains (By similarity). Plays a role in the multivesicular body (MVB) sorting pathway. Required for ubiquitin-dependent sorting of proteins into the endosome and subsequent trafficking to the vacuole. May regulate MVB sorting through deubiquitination of ubiquitinated ESCRT proteins. Binds 2 Zn(2+) ions per subunit. The JAMM motif is essential for the protease activity. Belongs to the peptidase M67C family.