Structural requirements for formyl homooligopeptide chemoattractants.

Using solution peptide synthesis, we have made three series of N alpha-formylated homooligopeptides, from the dipeptide to the heptapeptide, derived from L-methionine, L-norleucine, and S-methyl-L-cysteine and related to the chemotactic peptide N alpha-formylmethionylleucylphenylalanine. Compounds were prepared to determine the combined effects of the main-chain length and the presence of a sulfur atom in side-chain gamma- and delta-positions. Each peptide was tested for its ability to induce rabbit peritoneal polymorphonuclear leukocytes in the presence of cytochalasin B to secrete granule enzymes. In parallel, a conformational analysis was carried out in the solid state and in solution, using infrared absorption and circular dichroism. We examined these peptides in solvents of widely different polarities, i.e., chloroform, 2,2,2-trifluoroethanol, 1,1,1,3,3,3-hexafluoropropan-2-ol, and mixed organic-aqueous media. The tendencies to form antiparallel-chain beta-associated and folded structures were determined. The biological and conformational data are described in terms of a model of the chemotactic peptide receptor of rabbit neutrophils recently proposed by Freer et al. (1982) [Freer, R.J., Day, A.R., Muthukumarswamy, N., Pinon, D., Wu, A., Showell, H.J., & Becker, E.L. (1982) Biochemistry 21, 257-263]. In the three N alpha-formylated C-methoxy homooligopeptide series tested, the highest level of activity attained is at the tetrapeptide or pentapeptide stage, confirming the suggestion that the formylpeptide receptor is large enough to accommodate a peptide with at least four amino acid residues.(ABSTRACT TRUNCATED AT 250 WORDS)