Selective Degradation of Multimeric Proteins Via Chemically Induced Proximity to TRIM21

Targeted protein degradation (TPD) has emerged as an effective strategy to eliminate disease-causing proteins by inducing their interactions with the protein degradation machinery. First-generation TPD agents exploit a limited set of broadly expressed E3 ubiquitin ligases with constitutive activity, forbidding their application to proteins requiring higher levels of targeting selectivity. Here, by phenotype-based screening, we discovered that the antipsychotic drug acepromazine possesses interferon-enhanced cytotoxicity towards cancer cell lines expressing high levels of aldo-keto reductases 1C. These enzymes convert acepromazine into its stereo-selective metabolite ( S )-hydroxyl-acepromazine, which recruits the interferon-induced E3 ubiquitin ligase TRIM21 to the vicinity of the nuclear pore complex, resulting in the degradation of nuclear pore proteins. Co-crystal structures of acepromazine and derivatives in complex with the PRYSPRY domain of TRIM21 revealed a ligandable pocket, which was exploited for designing heterobifunctional degraders. The resulting chemicals selectively degrade multimeric proteins— such as those in biomolecular condensates—without affecting monomeric proteins, consistent with the requirement of substrate-induced clustering for TRIM21 activation. As aberrant protein assemblies have been causally linked to diseases such as neurodegeneration, autoimmunity, and cancer, our findings highlight the potential of TRIM21-based multimer-selective degraders as a strategy to tackle the direct causes of these diseases.### Competing Interest StatementThe authors have declared no competing interest.