Molecular glue CELMoD compounds are allosteric regulators of cereblon conformation

Cereblon (CRBN) is an ubiquitin ligase (E3) adaptor protein co-opted by CRBN E3 Ligase Modulatory Drugs (CELMoD) agents that target therapeutically-relevant proteins for degradation. Prior crystallographic studies defined the drug-binding site within CRBNs Thalidomide Binding Domain (TBD), but the allostery of drug-induced neosubstrate binding remains unclear. We therefore performed cryo-EM analyses of the DDB1[~]CRBN apo-complex, and compared these structures with DDB1[~]CRBN in the presence of CELMoD compounds alone and complexed with neosubstrates. Association of CELMoD compounds to the TBD is necessary and sufficient for triggering CRBN allosteric rearrangement from an "open" conformation to the canonical "closed" conformation. Importantly, the neosubstrate Ikaros only stably associates with the closed CRBN conformation, illustrating the importance of allostery for CELMoD compound efficacy, and informing structure-guided design strategies to improve therapeutic efficacy.