Chemical modification of Bacillus thuringiensis subsp. thuringiensis (HD-524) trypsin-activated endotoxin: Implication of tyrosine residues in lepidopteran cell lysis

Abstract

A purified protein fraction from a solubilized and trypsin-digested extract of Bacillus thuringiensis subsp. thuringiensis (HD-524) fermentation powder was lytic to cells from several lepidopteran lines. Maximum yield was obtained by alkaline carbonate-thiocyanate solubilization of washed powder followed by trypsin digestion and Sephacryl (S-300) chromatography. The alkaline carbonate-solubilized fraction consisted predominantly of two bands on sodium dodecyl sulfatepolyacrylamide gel electrophoresis with MW of 144 ± 0.9 kDa and 134 ± 1.4 kDa. After trypsin treatment and column chromatography, the cytolytic fraction consisted of a major band with a MW of 60.0 ± 1.8 kDa and a minor band of 69 ± 0.9 kDa. Cells from Trichoplusia ni (TN368) were most susceptible to lysis with 50% of cells lysed at 3 μg/ml, followed by Spodoptera frugiperda cells (SF21AE) exhibiting 50% cell lysis at 5 μg/ml and Lymantria dispar cells (Ld652Y) showing 40% lysis at 10 μg/ml. Chemical modification of the polypeptides was performed to determine the role of certain amino acid residues in the cytolytic activity. The group-specific reagent tetranitromethane was used to nitrate and oxidize tyrosine and cysteine residues, respectively. Cysteine residues alone were also modified with p-hydroxymercuribenzoic acid. Lysine residues were modified with O-methylisourea. Of the three types of amino acid residues, only the modification of tyrosine resulted in reduced cell lysis.