Ahmad W, Ellar D J
Department of Biochemistry, University of Cambridge, U.K.
FEMS Microbiol Lett. 1990 Mar 1;56(1-2):97-104. doi: 10.1016/0378-1097(90)90132-a.
Comparison of the sequences of Bacillus thuringiensis entomocidal toxins of widely differing specificity reveals six conserved domains. The role of one of the most highly conserved domains (D1) located near the N-terminus has been investigated by site directed mutagenesis at two positions. Although preliminary results indicate that the capacity of the mutants to bind to putative receptors on the plasma membrane of susceptible cells was unaffected, toxicity in vivo was reduced by 70-80%. The role of the highly hydrophobic segment exposed at the N-terminus of the toxin after proteolytic activation was investigated by substituting two aspartate residues for phenylalanine and valine located adjacent to each other in the centre of this segment. The toxicity of the resulting mutant protein was only 40% of the unmutated toxin but again preliminary results suggest that binding to putative receptors was unaffected. These results suggest that regions close to the N-terminus of this and similar toxins may play an important role in the membrane insertion event which is believed to follow receptor recognition.
对具有广泛不同特异性的苏云金芽孢杆菌杀虫毒素序列进行比较，发现了六个保守结构域。通过在两个位置进行定点诱变，研究了位于N端附近的一个高度保守结构域（D1）的作用。虽然初步结果表明突变体与敏感细胞质膜上假定受体结合的能力未受影响，但体内毒性降低了70 - 80%。通过将位于该片段中心彼此相邻的两个天冬氨酸残基替换为苯丙氨酸和缬氨酸，研究了毒素经蛋白水解激活后在N端暴露的高度疏水片段的作用。所得突变蛋白的毒性仅为未突变毒素的40%，但初步结果再次表明与假定受体的结合未受影响。这些结果表明，这种毒素及类似毒素靠近N端的区域可能在据信继受体识别之后发生的膜插入事件中起重要作用。
