Mov34/MPN/PAD-1 family: nuclear protein localization-4 (Npl4) domain
Npl4p (nuclear protein localization-4) is identical to Hmg-CoA reductase degradation 4 (HRD4) protein and contains a domain that is part of the pfam clan MPN/Mov34-like. Npl4 plays an intermediate role between endoplasmic reticulum-associated degradation (ERAD) substrate ubiquitylation and proteasomal degradation. Npl4p associates with Cdc48p (Cdc48 in yeast and p97 or valosin-containing protein (VCP) in higher eukaryotes), the highly conserved ATPase of the AAA family, via ubiquitin fusion degradation-1 protein (Ufd1p) to form a Cdc48p-Ufd1p-Npl4p complex which then functions in the recognition of several polyubiquitin-tagged proteins and facilitates their presentation to the 26S proteasome for processive degradation. This family of eukaryotic MPN-like domains lacks the key residues that coordinate a metal ion and therefore does not show catalytic isopeptidase activity.