The Zinc Finger of NEMO Is a Functional Ubiquitin-binding Domain

NEMO (NF-κB essential modulator) is a regulatory protein essential to the canonical NF-κB signaling pathway, notably involved in immune and inflammatory responses, apoptosis, and oncogenesis. Here, we report that the zinc finger (ZF) motif, located in the regulatory C-terminal half of NEMO, forms a specific complex with ubiquitin. We have investigated the NEMO ZF-ubiquitin interaction and proposed a structural model of the complex based on NMR, fluorescence, and mutagenesis data and on the sequence homology with the polymerase η ubiquitin-binding zinc finger involved in DNA repair. Functional complementation assays and in vivo pull-down experiments further show that ZF residues involved in ubiquitin binding are functionally important and required for NF-κB signaling in response to tumor necrosis factor-α. Thus, our findings indicate that NEMOZFisa bona fide ubiquitin-binding domain of the ubiquitin-binding zinc finger type.