In vitro systems for NEDD8 conjugation by Ubc12

Nedd8 is a ubiquitin-like molecule that is highly conserved in eukaryotes. Similar to ubiquitin, Nedd8 attaches to target proteins through an enzymatic cascade composed of Nedd8-specific E1 (activating)- and E2 (conjugating)-enzymes. The E1 for Nedd8 is a heterodimer of APP-BP1 and Uba3, while the E2 is Ubc12. The most well-characterized targets of Nedd8 are proteins of the Cullin family, a core component of SCF (Skp1/Cullin1/F-box proteins) and/or SCF-like ubiquitin ligase complexes. The Nedd8 modification of Cullin (Cul) family proteins is evolutionarily conserved, and genetic analyses in various organisms suggest a positive role of the NEDD8 for the function of Cul family proteins. Further biochemical analysis reveals that NEDD8 modification augments the ubiquitin ligase activity of Cullin-based complexes through the recruitment of ubiquitin-charged E2 to the complex. This chapter describes methods for the purification of NEDD8 conjugation enzymes and in vitro Nedd8 conjugation.