Metalloprotease component of the 26S proteasome that specifically cleaves 'Lys-63'-linked polyubiquitin chains. The 26S proteasome is involved in the ATP-dependent degradation of ubiquitinated proteins. The function of the 'Lys-63'-specific deubiquitination of the proteasome is unclear (By similarity). Component of the 19S regulatory cap of the 26S proteasome. Belongs to the peptidase M67A family. PSMD14 subfamily.