Essential structural requirements for triggering of mast cells by a synthetic peptide comprising a sequence in the C epsilon 4 domain of human IgE

A range of synthetic analogues of the peptides Lys-Thr-Lys-Gly-Ser-Gly-Phe-Phe-Val-PheNH2 (human IgE epsilon-chain 497-506 decapeptide) and Lys-Thr-Lys-Gly-Ser-Gly-Phe-PheNH2 (epsilon-chain 497-504 octapeptide) were tested for activity as releasers of 5-hydroxytryptamine from rat peritoneal mast cells. The following structural modifications were found to abrogate activity: N-acetylation of the alpha-amino group of the N-terminal lysine residue; substitution of the two lysine residues by either serine or glutamine; depletion of the two C-terminal hydrophobic residues (Val-Phe) of the decapeptide; and substitution of phenylalanine by alanine in the C-terminal position of the octapeptide. These observations point to a requirement for positively charged amino acids and hydrophobic amino acids at the N- and C-terminus respectively for triggering of mast cells by these short-chain peptides. Releasing activity was also found to depend on the stereospecific conformation of the positively charged region, since substitution of L-isomeric amino acids by D-isomeric forms in the three N-terminal positions of the decapeptide led to loss of potency. Inactive analogues of the decapeptide and octapeptide, at concns up to 10(-4) M, failed to antagonise the mediator-releasing effects of the active decapeptide at concns of 3 X 10(-6) - 10(-4) M.