Investigating protein degradability through site-specific ubiquitin ligase recruitment.

We report targeted protein degradation through the site-specific recruitment of native ubiquitin ligases to a protein of interest conjugation of E3 ligase ligands. Direct comparison of degradation ability of proteins displaying the corresponding bioconjugation handle at different regions of protein surfaces was explored. We demonstrate the benefit of proximal lysine residues and investigate flexibility in linker length for the design of optimal degraders. Two proteins without known small molecule ligands, EGFP and DUSP6, were differentially degraded when modified at different locations on their protein surfaces. Further, the cereblon-mediated degradation of the known PROTAC target ERRα was improved through the recruitment of the E3 ligase to regions different from the known ligand binding site. This new methodology will provide insight into overall protein degradability, even in the absence of a known small molecule ligand and inform the process of new ligand and PROTAC development to achieve optimal protein degradation. Furthermore, this approach represents a new, small molecule-based conditional OFF switch of protein function with complete genetic specificity. Importantly, the protein of interest is only modified with a minimal surface modification (<200 Da) and does not require any protein domain fusions.