E2 enzyme inhibition by stabilization of a low-affinity interface with ubiquitin

In the ubiquitin-proteasome system, E2 enzymes such as Cdc34A mediate the transfer of ubiquitin to protein substrates, which are thus marked for proteasomal degradation or other fates. New structural data reveal that the small-molecule inhibitor CC0651 impairs Cdc34A activity by stabilizing the normally transient Cdc34A–ubiquitin complex.