Fine-tuning an intracellular allosteric pocket programs GPCR signaling bias

Fine-tuning the intracellular allosteric pocket of neurotensin receptor 1 (NTSR1) by modifying the {beta}-arrestin-biased ligand SBI-553 reshapes G-protein versus {beta}-arrestin signaling profiles.

• Why it matters: Intracellular allosteric ligands can bias GPCR signaling, but how small chemical changes in these pockets alter receptor–transducer coupling and downstream pathways is unclear.
• What they did: The study chemically modified SBI-553, solved cryo-electron microscopy structures of NTSR1–{beta}-arrestin2 with designed probes, and used alanine scanning plus phosphoproteomics; it also tested SBI-553 and N065 in mice.
• The result: Ligand-dependent remodeling of the intracellular cavity and transducer-sensitive residues produced distinct signaling and partially overlapping phosphoproteomic profiles, and N065 improved survival in a lethal endotoxemia model.