Ubiquitin Receptor-Induced Proximity is Sufficient for Ubiquitin-Independent Targeted Protein Degradation via the 26S Proteasome

Abstract

The 26S proteasome engages with ubiquitinated substrates primarily through its constituent ubiquitin (Ub) receptors, which initiates a cascade of proteolytic processes. Leveraging this recognition mechanism, we developed a targeted protein degradation (TPD) strategy that recruits substrates directly to the proteasome, thereby bypassing the ubiquitination step. Our proteasome-targeting chimera, Protea-Tac, is a heterobifunctional protein degrader composed of a Ub receptor and an intracellular antibody. This chimera integrates into 26S proteasomes without altering their functional integrity. Localization of target proteins, including c-Fos, BRD4, Flag-TDP43, HA-tau, and GFP-ODC, to the proteasome via Protea-Tac with cognate antibodies resulted in their induced degradation. We demonstrated that this platform is 1) modular, allowing facile switching between targets; 2) Ub-independent; and 3) highly target-specific. Protea-Tac exhibited in vivo anti-tumor efficacy, degrading c-Fos and substantially delaying tumor growth. Overall, these findings identify Protea-Tac as a distinct TPD modality capable of directly degrading intracellular proteins via engineered 26S proteasomes. TeaserProtea-Tac is a heterobifunctional protein degrader that enables Ub-independent TPD, exhibits high specificity and modularity, and demonstrates in vivo applicability.