Use of synthetic peptides to probe functional domains of a Bacillus thuringiensis toxin

Two 10-residue peptides exhibiting sequence homology to CryIA(a) toxin were chemically synthesized. One corresponds to a segment from residues 48-57 (peptide A) and is common to all CryIA toxins and the second corresponds to a segment from residues 348-357 (peptide B) and is specific to the CryIA(a) toxin. Antibodies were raised in rabbits against both peptides. Antipeptide A did not protect either Bombyx mori or Choristoneura fumiferana larvae against CryIA(a) toxin. However, antipeptide B offered significant protection to B. mori and somewhat less protection to C. fumiferana larvae. Neither antiserum interfered with the binding of CryIA(a) toxin to brush border membrane vesicles of either insect. The results suggest that the segment from residues 348-357 in CryIA(a) toxin is important for expression of toxicity in both insects but not for binding.