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-PheNH 2 (human IgE e-chain 497–506 decapeptide) and Lys-Thr-Lys-Gly-Ser-Gly-Phe-PheNH 2 (e-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 α-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 × 10 −6 — 10 −4 M .