Beyond the G-Loop: CRBN Molecular Glues Potently Target VAV1 via a Novel SH3 RT-Loop Degron

This study reports the discovery and characterization of novel CRBN molecular glues that selectively induce the proteasomal degradation of the hematopoietic-specific signaling protein VAV1, a key target in hematological malignancies and autoimmune diseases. Utilizing unbiased global proteomics, we identified phenyl-glutarimide derivatives NGT-201-12, as effective VAV1 degraders, with its C-terminal SH3 domain (SH3-2) being crucial for this interaction. A significant finding is the elucidation of a non-canonical RT-loop degron (RDxS motif, residues 796-799) within VAV1 SH3-2, distinct from previously characterized G-loop degrons. This discovery, supported by advanced computational modeling using the physics- and AI-driven GluePlex workflow and validated by site-directed mutagenesis, highlights versatility of CRBN in recognizing diverse neosubstrate motifs. Furthermore, we demonstrate that applying Free Energy Perturbation (FEP+) calculations to these predicted ternary structures yields cooperativity metrics that correlate with experimental degradation potency, overcoming the limitations of standard molecular docking. This establishes a robust workflow where, once a ternary complex is predicted--even with initial weak binders--FEP+ can be utilized to prospectively rank analogs and optimize molecular glue potency. Additionally, we demonstrate that strategic chemical modifications, particularly conformational restriction via halogen substitution (e.g., NGT-201-18), markedly potentiate VAV1 degradation, a principle supported by density functional theory (DFT) calculations. Comprehensive structure-activity relationship (SAR) studies provided a roadmap for designing next-generation VAV1 degraders. Importantly, dose-response proteomics not only confirmed VAV1 as the primary target but also revealed LIMD1, possessing a canonical G-loop, as an off-target for some analogs, indicating a single molecular glue can engage disparate degron motifs. The identification of the VAV1 RT-loop degron prompted a proteome-wide search, revealing other SH3-containing proteins as potential targets or off-targets. In conclusion, this research unveils a novel non-canonical RT-loop degron in VAV1, demonstrates the utility of conformational restriction in enhancing degrader potency, and underscores the critical role of integrating global proteomics with advanced structural modeling and FEP calculations for understanding degrader potency and selectivity. These findings offer a promising therapeutic strategy for targeting VAV1 and significantly expand the landscape of CRBN neosubstrate recognition and the rational design of molecular glue degraders.