Mpr1p, Pad1p N-terminal (MPN) domains with catalytic isopeptidase activity (metal-binding); eukaryoticThis family contains eukaryotic MPN (also known as Mov34, PAD-1, JAMM, JAB, MPN+) domains found in proteins with a variety of functions, including AMSH (associated molecule with the Src homology 3 domain (SH3) of STAM), H2A-DUB (histone H2A deubiquitinase), BRCC36 (BRCA1/BRCA2-containing complex subunit 36), as well as Rpn11 (regulatory particle number 11) and CSN5 (COP9 signalosome complex subunit 5). These domains contain the signature JAB1/MPN/Mov34 metalloenzyme (JAMM) motif, EXnHS/THX7SXXD, which is involved in zinc ion coordination and provides the active site for isopeptidase activity. Rpn11 is responsible for substrate deubiquitination during proteasomal degradation. It is essential for maintaining a correct cell cycle and normal mitochondrial morphology and physiology. CSN5 is critical for nuclear export and the degradation of several tumor suppressor proteins, including p53, p27, and Smad4. Over-expression of CSN5 has been implicated in cancer initiation and progression. AMSH specifically cleaves Lys 63 and not Lys48-linked polyubiquitin (poly-Ub) chains, thus facilitating the recycling and subsequent trafficking of receptors to the cell surface. It is involved in the degradation of EGF receptor (EGFR) and possibly other ubiquitinated endocytosed proteins. BRCC36 is part of the BRCA1/BRCA2/BARD1-containing nuclear complex that displays an E3 ubiquitin ligase activity; it is targeted to DNA damage foci after irradiation. 2A-DUB is specific for monoubiquitinated H2A (uH2A), regulating transcription by coordinating histone acetylation and deubiquitination, and destabilizing the association of linker histone H1 with nucleosomes. It is a positive regulator of androgen receptor (AR) transactivation activity on a reporter gene and serves as a marker in prostate tumors.