Structural Studies of βTrCP Reveal Plasticity in Binding Modes of Consensus and Nonconsensus Degrons

The E3 ligase βTrCP regulates a significant number of important cytosolic proteins by recognizing and binding to a "DSGXXS" consensus phosphodegron sequence, resulting in the ubiquitination and degradation of target proteins. While many of the substrates of βTrCP have strong disease links, there is high-resolution structural data available for just one of these proteins in complex with βTrCP. Here, we describe the development of a robust crystallographic system for βTrCP and report high-resolution crystal structures for βTrCP in complex with degrons from five new targets, encompassing the important cancer proteins, WEE1, claspin, ATF4, PDCD4, and IκBα. Interestingly, these structures reveal the molecular basis by which βTrCP can recognize and bind both consensus and nonconsensus degron peptides and reveal an overall general plasticity in degron binding mode. We also provide a biochemical assessment of the binding affinities of these peptides for βTrCP, adding further insight into the molecular interactions observed in the crystal structures. Finally, computational analyses of the βTrCP complexes identify opportunities for potential molecular glue approaches.