NEDD8 (neural precursor cell expressed developmentally downregulated gene 8) is an ubiquitin-like protein, with approximately 60% identity to ubiquitin (the highest homology of any ubiquitin-like protein). Conjugation of mature NEDD8 (via its exposed C-terminal glycine residue) to specific lysine residues on a limited number of cellular target proteins via isopeptide bonds, allows NEDD8 to play a critical regulatory role in cell proliferation and development.

The NEDD8 conjugation pathway proceeds by a mechanism analogous to that of the ubiquitin conjugation cascade, consisting of a dedicated NEDD8 E1 activating enzyme (a heterodimeric complex consisting of a regulatory subunit APP-BP1 and a catalytic subunit Uba3), E2 conjugating enzyme (UbcH12) and substrate specific E3 ligases.

An increasing number of substrates for NEDDylation, including the tumor suppressors p53 and VHL, and EGFR have been identified in addition to members of the well-characterized cullin family of proteins, that play a structural role in ubiquitin E3 ligase complexes such as SCF.

Cullin NEDDylation in SCF complexes is facilitated by the RING domain containing Rbx1 (Roc1) SCF subunit, which is thought to act as a NEDD8 E3 ligase, and enhances the complex’s ubiquitin E3 ligase activity.

NEDDylation of p53 is mediated by its ubiquitin E3 ligase Mdm2, providing an additional control mechanism for inhibition of its transcriptional activity. E3 independent NEDDylation of p53 has also been demonstrated in vitro. Reconstitution of the NEDD8 conjugation pathway in vitro using recombinant proteins is readily achieved and has been used to investigate a number of NEDD8 modification systems.