Multiplexed assessment of human degradation signals

Degrons are short protein segments that target proteins for degradation via the ubiquitin-proteasomesystem and thus ensure timely removal of signaling proteins and clearance of misfolded proteins fromthe intracellular space. Here, we describe a systematic screen for degrons in the human cytosol. Wedetermine degron potency of >200,000 different 30-residue tiles from more than 5,000 cytosolichuman proteins with 99.7% coverage. In total, 19.1% of the tiles function as strong degrons, 30.4%as intermediate degrons, while 50.5% did not display degron properties. The vast majority of thedegrons are dependent on the E1 ubiquitin-activating enzyme and the proteasome but independent ofautophagy. The results reveal both known and novel degron motifs, both internal as well as at the C-terminus. Mapping the degrons onto protein structures, predicted by AlphaFold2, revealed that mostof the degrons are located in buried regions, indicating that they only become active upon unfoldingor misfolding. Training of a machine learning model allowed us to probe the degron properties furtherand predict the cellular abundance of missense variants that operate by forming degrons in exposedand disordered protein regions, thus providing a mechanism of pathogenicity for germline codingvariants at such positions.