Boc3Arg-Linked Ligands Induce Degradation by Localizing Target Proteins to the 20S Proteasome.

Targeted protein degradation is a promising strategy for drug design and functional assessment. Several small molecule approaches have been developed that localize target proteins to ubiquitin ligases, inducing ubiquitination and subsequent degradation by the 26S proteasome. We discovered that the degradation of a target protein can also be induced by a recognition ligand linked to tert-butyl carbamate (Boc3)-protected arginine (B3A). Here, we show that this process requires the proteasome but does not involve ubiquitination of the target protein. B3A does not perturb the structure of the target protein; instead, a B3A-ligand stabilizes its target protein. B3A ligands stimulate activity of purified 20S proteasome, demonstrating that the tag binds directly to the 20S proteasome. Moreover, purified 20S proteasome is sufficient to degrade target proteins in the presence of their respective B3A-linked recognition ligands. These observations suggest a simple model for B3A-mediated degradation wherein the B3A tag localizes target proteins directly to the 20S proteasome. Thus, B3A ligands are the first example of a ubiquitin-free strategy for targeted protein degradation.