A HIGH POTENCY NONFORMYLATED PEPTIDE AGONIST FOR THE PHAGOCYTE N-FORMYLPEPTIDE CHEMOTACTIC RECEPTOR

Analysis of synthetic tri- and tetrapeptides has previously indicated that N-formylation is required for high biological activity when they react with the phagocyte N-formylpeptide receptor, suggesting that the natural ligand for the receptor is from bacterial and/or mitochondria l sources. To explore this requirement further, we synthesized the pen tapeptide thionyl-norleucyl-leucyl-phenylalanylphenylalanine (MNleLFF) and studied the effects of different NH2-terminal modifications on it s activity. N-formyl-MNleLFF induced transient alterations of [Ca2+](i ) and superoxide production in human neutrophils with 10- and 100-fold greater potency, respectively, than the prototype N-formylpeptide, N- formylmethionyl-leucyl-phenylalanine (fMLF). Surprisingly, N-acetyl-MN leLFF was as potent as N-formyl-MNleLFE Moreover, the unacylated count erpart H-MNleLFF was also highly active, having an EC(50) for calcium mobilization of 10 nM, and for respiratory burst activation of 100 nM. All three pentapeptides could completely desensitize calcium transien ts elicited by stimulation of neutrophils with fMLF, whereas the neutr ophil chemoattractants C5a and interleukin 8 only weakly affected fMLF -induced transients, suggesting that they activate neutrophils via the same receptor as fMLF Finally, all three pentapeptides activated the recombinant human N-formylpeptide receptor expressed in frog oocytes, but did not effectively activate related phagocyte receptors. These da ta broaden the potential sources of natural ligands for the N-formylpe ptide receptor from N-formylated bacterial and mitochondrial products to other nonformylated endogenous peptides.