Studies on fMLP-receptor interaction and signal transduction pathway by means of fMLP-OMe selective analogues

For-Thp-Leu-Ain-OMe ([Thp(1), Ain(3)] fMLP-OMe) (2), for-Met-Delta(2)Leu Ph e-OMe ([Delta(t)Leu(2)] fMLP-OMe) (3), for-Thp-Leu-Phe OMe ([Thp(1)] fMLP-O Me) (4), and for-Met-Leu-Ain-OMe ([Ain(3)] fMLP-OMe) (5) are for-Met-Leu-Ph e-OMe (fMLP-OMe) (1) analogues which discriminate between different respons es of human neutrophils. Peptides 3 and 5, similar to fMLP-OMe, enhance neu trophil cyclic AMP (cAMP) as well as calcium levels, while analogues 2 and 4, which evoke only chemotaxis, do not alter the concentration of these int racellular messengers. When we tested the peptides' ability to displace [H- 3]-fMLP from its binding sites, the following order of potency was observed : analogue 1 > 3 > 5 > 2 > 4. A particularly low activity at the receptor l evel characterized analogues 2 and 4. Their low effectiveness was not impro ved by the addition of cytochalasin B, by different incubation temperatures , or by the absence of endogenous guanine nucleotides, conditions known to influence fMLP receptor fate and functionality. We speculate that, in certa in conditions, the fMLP receptor may undergo conformational changes that im pede the binding of pure chemoattractants. (C) 2000 Elsevier Science Inc. A ll rights reserved.