Identification of an allosteric site on the E3 ligase adapter cereblon

Cereblon (CRBN) is the target of thalidomide derivatives¹ that achieve therapeutic efficacy against some haematologic neoplasias^2-4 by recruiting neosubstrates for degradation^5-7. Despite the intense investigation of orthosteric thalidomide derivatives, little is known about alternate binding sites on CRBN. Here we report an evolutionarily conserved cryptic allosteric binding site on CRBN. Small-molecule SB-405483 binds the allosteric site to cooperatively enhance the binding of orthosteric ligands and alter their neosubstrate degradation profiles. A survey of over 100 orthosteric ligands and their degradation targets reveals trends in the classes of compounds and neosubstrates in which degradation outcomes are enhanced or inhibited by SB-405483. Structural investigations provide a mechanistic basis for the effects of the allosteric ligand by shifting the conformational distribution of CRBN^open to a novel CRBN^int and increasing the CRBN^closed state. The discovery of a cryptic allosteric binding site on CRBN that alters the functional effects of orthosteric ligands opens new directions with broad implications for improving the selectivity and efficacy of CRBN therapeutics.