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-Met6 resulted in loss of activity, removal of Val5 together with d-Met6 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 Lys2 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 Trp1 and Tyr3, hydrophobic interaction of Nle2, and the thio-based hydrogen bonding of Met4, 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.