Inhibition of binding of rat IgE to rat mast cells by synthetic IgE peptides.

Seven synthetic peptides corresponding to amino acid sequences located within various surface regions of the CH3 and CH4 domains of rat IgE were tested for their capacity to compete with intact rat IgE for binding sites on mast cells. Peptides representing rat IgE sequences 414-428 (P129), 459-472 (P124), 491-503 (P128) and 542-557 (P123) inhibited the binding of 125I-labeled rat IgE to mast cells by between 25-50% at concentrations between 10(-5)-10(-4) M. Three other rat IgE sequences, 378-396 (P130), 522-535 (P122) and 560-571 (P131), and three non-IgE peptides demonstrated no inhibitory activity. On a molar basis, the most active peptide, P129, was approximately 1000-times less active than native rat IgE. Furthermore, extensive washing of cells incubated with this peptide did not reduce its ability to inhibit the subsequent binding of 125I-labeled rat IgE. These results suggest that residues within sequences 414-428, 459-473, 491-503 and 542-557 may contribute towards the mast cell receptor binding site on rat IgE.