Agonist-dependent phosphorylation of the formyl peptide receptor is regulated by the membrane proximal region of the cytoplasmic tail

Formyl peptide receptor (FPR) is a chemoattractant G protein-coupled receptor (GPCR) involved in the innate immune response against bacteria. Receptor activation is terminated by receptor phosphorylation of two serine- and threonine-rich regions located in the distal half of the cytoplasmic tail. In this study we show that introduction of an amino acid with a bulky side chain (leucine or glutamine) adjacent to a single leucine, L320, in the membrane-proximal half of the cytoplasmic tail, significantly enhanced receptor phosphorylation, β-arrestin1/2 translocation, and receptor endocytosis, without affecting Gi-mediated ERK1/2 activation and release of intracellular calcium. In addition, the point mutations resulted in diminished susceptibility to trypsin, suggesting a conformation different from that of wild type FPR. Alignment of the FPR sequence with the rhodopsin sequence showed that L320 resides immediately C-terminal of an amphipathic region that in rhodopsin forms helix 8. Deletion of seven amino acids (Δ309–315) from the predicted helix 8 of FPR (G307–S319) caused reduced cell signaling as well as defects in receptor phosphorylation, β-arrestin1/2 translocation and endocytosis. Thus, the amino acid content in the N-terminal half of the cytoplasmic tail influences the structure and desensitization of FPR.