A Toxic Fragment from the Entomocidal Crystal Protein of<i>Bacillus thuringiensis</i>

Abstract

Purified crystal protein from Bacillus thuringiensis subsp. dendrolimus strain T84A1 gave a single polypeptide band (apparent mol. wt. 145,000) on SDS-PAGE and the only N-terminal amino acid sequence was Met–Asp–Asn–Asn–Pro–Asn–Ile–. No pentose or hexose was detected. Solid phase tryptic digestion of the solubilized crystal protein bound on a DEAE-cellulose column was found to be a successful method to prepare a toxic fragment without denaturation. The resulting fragment (fragment T) was slightly basic (pI 8.9) and the molecular weight was estimated as 58,000 on SDS-PAGE and by gel filtration without denaturing agents. The apparent number of the amono acid residues was 516 and the N- and C-terminal sequences were determined as Ile–Glu–X–Gly–Tyr–Thr– and –Leu–Arg, respectively. The molar specific toxicities of the solubilized crystal protein and fragment T were nearly identical. The fragment T retained the full toxicity and selectivity of the intat crystal protein. Location of the fragment T in the crystal protein is also discussed.