Elucidation of E3 Ubiquitin Ligase Specificity Through Proteome-wide Internal Degron Mapping
The ubiquitin-proteasome system plays critical roles in biology by regulating protein degradation. Despite their importance, precise recognition specificity is known for few of the 600 E3s. Here we establish a two-pronged strategy for identifying and mapping critical residues of internal degrons on a genome scale in HEK-293T cells.  We employ Global Protein Stability profiling combined with machine learning to identify 15,800 peptides likely to contain sequence-dependent degrons. We combine this with scanning mutagenesis to define critical residues for over 5,000 predicted degrons.  Focusing on Cullin-RING ligase degrons, we generated mutational fingerprints for 219 degrons and developed DegronID, a computational algorithm enabling the clustering of degron peptides with similar motifs.  CRISPR analysis enabled the discovery of E3-degron pairs of which we uncover 16 pairs that revealed extensive degron variability and structural determinants. We provide the visualization of this data on the public DegronID Data Browser as a resource for future exploration. Overall design: We performed the global protein stability (GPS) in HEK-293T cells using a human peptidome and performed CRISPR screens with an sgRNA library targetting genes related to the ubiquitin proteasome system.