Molecular basis for the unique deubiquitinating activity of the NF-kappaB inhibitor A20.
Nuclear factor kappaB (NF-kappaB) activation in tumor necrosis factor, interleukin-1, and Toll-like receptor pathways requires Lys63-linked nondegradative polyubiquitination. A20 is a specific feedback inhibitor of NF-kappaB activation in these pathways that possesses dual ubiquitin-editing functions. While the N-terminal domain of A20 is a deubiquitinating enzyme (DUB) for Lys63-linked polyubiquitinated signaling mediators such as TRAF6 and RIP, its C-terminal domain is a ubiquitin ligase (E3) for Lys48-linked degradative polyubiquitination of the same substrates. To elucidate the molecular basis for the DUB activity of A20, we determined its crystal structure and performed a series of biochemical and cell biological studies. The structure reveals the potential catalytic mechanism of A20, which may be significantly different from papain-like cysteine proteases. Ubiquitin can be docked onto a conserved A20 surface; this interaction exhibits charge complementarity and no steric clash. Surprisingly, A20 does not have specificity for Lys63-linked polyubiquitin chains. Instead, it effectively removes Lys63-linked polyubiquitin chains from TRAF6 without dissembling the chains themselves. Our studies suggest that A20 does not act as a general DUB but has the specificity for particular polyubiquitinated substrates to assure its fidelity in regulating NF-kappaB activation in the tumor necrosis factor, interleukin-1, and Toll-like receptor pathways.
Pubmed ID: 18164316 RIS Download
Alanine | Amino Acid Sequence | Amino Acid Substitution | Binding Sites | Catalysis | Cell Line | Conserved Sequence | Crystallography, X-Ray | DNA-Binding Proteins | Escherichia coli | Gene Deletion | Glutathione Transferase | Humans | Hydrogen Bonding | Intracellular Signaling Peptides and Proteins | Kidney | Models, Molecular | Molecular Sequence Data | NF-kappa B | Nuclear Proteins | Polyubiquitin | Precipitin Tests | Protein Binding | Protein Structure, Secondary | Protein Structure, Tertiary | Sequence Homology, Amino Acid | Static Electricity | Substrate Specificity | TNF Receptor-Associated Factor 6 | Ubiquitin | Ubiquitin-Protein Ligases | Ubiquitination