Proteolysis Targeting Chimaeras (PROTACs) are heterobifunctional molecules that recruit a protein-of-interest (POI) to an E3 ubiquitin ligase enzyme to induce its ubiquitination and subsequent proteasomal degradation. In principle PROTACs could target any protein, even those that are currently considered “undruggable”, but target selection and pairing with an effective E3 ligase still present significant developmental bottlenecks.
Our work is therefore focussed upon the development of a high-throughput targeted protein degradation screening platform using engineered E3 ligases, known as bioPROTACs, modified to specifically engage and ubiquitinate given POIs via replacement of the endogenous substrate-recognition domain with a target-specific binding peptide. We have recently developed of a novel bioPROTAC degrader of β-catenin – a key downstream regulator of the Wnt signalling pathway – via conjugation of a short binding peptide derived from Axin to a truncated form of the E3 ligase βTrCP. Not only did this bioPROTAC display robust target knockdown and Wnt pathway suppression, but so too did it exemplify the modular nature of this system, with the binding peptide readily substitutable to transition between targets.
We now plan to extend this system to screen a library of approximately 450 human E3 ligases using various binding peptides directed against high-value oncogenic proteins. In doing so, we hope to identify effective POI-E3 ligase pairings to inform future small-molecule PROTAC development efforts.