IMMUNOGENICITY OF MASTOPARAN-B, A CATIONIC TETRADECAPEPTIDE ISOLATED FROM THE HORNET (VESPA-BASALIS) VENOM, AND ITS STRUCTURAL REQUIREMENTS

Mastoparan B (MP-B) is a cationic tetradecapeptide (LKLKSIVSWAKKVL-CON H2, mol. wt 1611) isolated from the black-bellied hornet (Vespa basali s) venom. The small peptide itself was capable of inducing antibodies without prior conjugation to a protein carrier in rabbits and mice. Th e mouse antibody was found to be of IgG(1) isotype with kappa-type lig ht chain. The peptide antigen was able to form insoluble complexes wit h the specific antibody, suggesting that MP-B possessed more than one epitope in its molecule. The finding that MP-B was able to bind with b oth mouse and rabbit antibodies in sandwich ELISA supports this conten tion. Synthetic MP-B analogues in which lysine at position 2, 4, 11 or 12 was replaced by neutral amino acids such as asparagine or leucine showed a significant decrease in their antibody-binding activities, Su bstitution of lysine at position 4 (Lys(4)) caused the most marked inh ibition in its binding activity, However, replacing tryptophan at posi tion 9 by tyrosine caused a relatively small reduction in its binding activity. Replacing both Lys(2,4) by asparagine or removing Lys-contai ning segments at amino or carboxyl terminus in MP-B sequence caused a remarkable decrease in the antibody-binding and immuno-genic activitie s of the peptide. The Lys residues located at amino and carboxyl termi nal segments of MP-B, especially Lys(4), appear to play a critical rol e in the binding interaction and the immunogenicity of the peptide.