Allosteric modulation of Grb2 drives ligand-dependent signal responses.

Adaptor proteins play a crucial role in signal transduction by facilitating the assembly of protein complexes at specific subcellular domains. These multifunctional molecules contain multiple binding modules that enhance the efficiency and flexibility of cellular signaling pathways, thereby orchestrating complex responses. Among these proteins, Grb2 (growth factor receptor-bound protein 2) emerges as a key regulator owing to its unique "sandwich" structure. Despite lacking intrinsic enzymatic activity, recent investigations have revealed that Grb2 acts not merely as a passive bridge but also utilizes intramolecular allosteric communication to modulate binding specificity. In this study, we compared the kinetic binding properties of SH2-SH3 belonging to Grb2 with Gab2 and the same experiment with bound states of the SH2 domain using two different peptides that mimics the physiological ligands of SH2. Our results demonstrate that the SH2 domain plays a critical regulatory role, exhibiting remarkably distinct behaviors in free and bound states, and depending on the ligand it binds to. This suggests how selectivity can be modulated by intradomain allostery. In vitro functional assays measuring the activation levels of the target protein further supported our hypothesis.