Development of PolyHis‐Targeting PROTAC Degraders

ABSTRACT Targeted protein degradation (TPD) via proteolysis targeting chimeras (PROTACs) enables selective removal of proteins of interest (POIs) by hijacking the ubiquitin‐proteasome system (UPS). However, broad application is constrained by the availability of high‐quality target ligands, which remain scarce for much of the human proteome, limiting assessment of POIs for UPS‐mediated degradation. To address this challenge, we developed polyhistidine‐targeting PROTACs (polyHisTACs) by conjugating a nickel‐nitrilotriacetic acid (Ni 2 + ‐NTA) headgroup to ligands of VHL or CRBN, thereby recruiting these E3 ligase complexes to polyHis‐tagged POIs. As expected, polyHisTACs effectively degraded CRISPR‐engineered, endogenously polyHis‐tagged BRD4 and also induced robust degradation of an exogenously expressed polyHis‐tagged RNA‐binding protein, PSPC1, a target that is typically considered undruggable. In summary, polyHisTACs overcome key limitations of existing tag‐based degrader systems by leveraging a minimal, easily implemented polyHis tag. This platform provides a versatile, reliable way to evaluate UPS‐mediated degradability in the absence of target‐specific ligands and serves as a practical tool for acute POI depletion in basic research.