A formyl peptide substituted with a conformationally constrained phenylalanine residue evokes a selective immune response in human neutrophils

Abstract Formyl-Met-Leu-Phe-OH (fMLP) binds to formyl peptide receptors, FPR1 and FPR2, and evokes migration and superoxide anion production in human neutrophils. To obtain a more effective and selective ligand, fMLP analogs in which the Phe residue was substituted with four isomers of cyclopropanephenylalanine were synthesized. While Z -isomer peptides induced both migration and superoxide anion production, E -isomer peptides elicited only chemotaxis. Homologous receptor desensitization experiments revealed that E -isomer peptides bound to FPR2. Although a selective agonist of chemotaxis also binds to FPR2 without increasing intracellular calcium concentration, E -isomer peptide elevated the concentration to the same level as fMLP. Understanding of mechanisms responsible for the selectivity of the reported selective agonists and ∇Phe-substituted analogs should prove useful for revealing the relationship between receptor–ligand interactions and biological responses of human neutrophils.