Discovery of Trp-Nle-Tyr-Met as a novel agonist for human formyl peptide receptor-like 1

Formyl peptide receptor-like 1 (FPRL1) is a structural homologue of FPR, which binds chemotactic peptides as small as three amino acids (e.g., fMet-Leu-Phe, fMLF) and activates potent bactericidal functions in neutrophils. In comparison, FPRL1 ligands include peptides of 6-104 amino acids, such as Trp-Lys-Tyr-Met-Val-[d]Met (WKYMVm) and other synthetic peptides. To determine the core peptide sequence required for FPRL1 activation, we prepared various analogues based on WKYMVm and evaluated their bioactivities in an FPRL1-transfected cell line. Although substitution of d-Met(6) resulted in loss of activity, removal of Val(5) together with d-Met(6) produced a peptide that retained most of the bioactivities of the parent peptide. The resulting peptide, WKYM, represents a core structure for an FPRL1 ligand. Further substitution of Lys(2) with Nle slightly improved the potency of the tetrapeptide, which selectively activates FPRL1 over FPR. Based on these structure-activity relationship studies, we propose a model in which the modified tetrapeptide Trp-Nle-Tyr-Met (WNleYM) binds to FPRL1 through aromatic interactions involving the side chains of Trp(1) and Tyr(3), hydrophobic interaction of Nle(2), and the thio-based hydrogen bonding of Met(4), with the respective residues in FPRL1 which have not been identified. The identification of the core sequence of a potent peptide agonist provides a structural basis for future design of peptidomimetics as potential therapeutic agents for FPRL1-related disorders.