Agonist-specific FPR1 conformational change prevents receptor recycling and promotes targeted protein degradation

Recycling of internalized cell surface receptors is critical for membrane transport and receptor-mediated signaling. Formyl peptide receptor 1 (FPR1) plays important roles in host defense and inflammatory tissue injury. Here we report that fMet–Leu–Phe–Cys (fMLFC), a peptide agonist of FPR1, prevents recycling of internalized FPR1 and diverts it to the late endosome and lysosome for degradation. In contrast, FPR1 bound to the classic ligand fMLF interacts with RAB11 and SNX17, facilitating its recycling back to the cell surface. We determined a cryo-EM structure of fMLFC-bound FPR1–Gi complex. Alanine substitutions of key residues that interact with fMLFC (F102A, T177A, F178A) improved FPR1 recycling. Using a FlAsH–NanoBRET-based FPR1 biosensor, the fMLFC-induced receptor conformational change was found to be different from the fMLF-induced conformational change. fMLFC stimulation reduced FPR1 cell surface expression, along with reduced acute lung injury in LPS-treated mice. Our findings suggest that fMLFC is a chemical knockdown agent that promotes targeted protein degradation and reduces FPR1-mediated inflammation. A peptide ligand binds FPR1 and induces changes in receptor conformation, thereby skewing the internalization-recycling pathway towards receptor degradation and reducing receptor-mediated inflammatory response in an animal model.