CC0651 is an allosteric inhibitor of the human Cdc34 ubiquitin-conjugating enzyme. CC0651 potently inhibits the ubiquitination of p27Kip1 (IC50: 1.72 μM).

p27Kip1 ubiquitination:1.72 μM

CC0651 acts by trapping a weak interaction between ubiquitin and the E2 donor ubiquitin-binding site. CC0651 completely inhibits the assembly of polyubiquitin chains and decreased formation of free triubiquitin and, to a lesser extent, hCdc34 monoubiquitin, but has no effect on the production of diubiquitin [1]. CC0651 strongly impairs the rate of ubiquitin chain initiation on the substrate by SCFCdc4, as measured by the monoubiquitination of Sic1 by K0 ubiquitin. CC0651 actually potentiates the formation of both ubiquitin dimers and monoubiquitinated hCdc34, concordant with the observed accumulation of the hCdc34 conjugate in cells treated with the ester derivative of CC0651. A quantitative SCF ubiquitination assay with a β-Catenin substrate peptide yields a value of IC50 of 18±1 μM for CC0651 inhibition, similar to the effective concentrations observed in the NMR and TR-FRET assays [2].