NEDD8 recruits E2-ubiquitin to SCF E3 ligase

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Abstract
NEDD8/Rub1 is a ubiquitin (Ub)‐like post‐translational modifier that is covalently linked to cullin (Cul)‐family proteins in a manner analogous to ubiquitylation. NEDD8 is known to enhance the ubiquitylating activity of the SCF complex (composed of Skp1, Cul‐1, ROC1 and F‐box protein), but the mechanistic role is largely unknown. Using an in vitro reconstituted system, we report here that NEDD8 modification of Cul‐1 enhances recruitment of Ub‐conjugating enzyme Ubc4 (E2) to the SCF complex (E3). This recruitment requires thioester linkage of Ub to Ubc4. Our findings indicate that the NEDD8‐modifying system accelerates the formation of the E2–E3 complex, which stimulates protein polyubiquitylation.