Carroll J, Convents D, Van Damme J, Boets A, Van Rie J, Ellar D J
Department of Biochemistry, University of Cambridge, United Kingdom.
J Invertebr Pathol. 1997 Jul;70(1):41-9. doi: 10.1006/jipa.1997.4656.
The Cry3A delta-endotoxin protein inclusion synthesized by Bacillus thuringiensis subsp. tenebrionis is soluble in alkaline and acid buffer solutions but the toxin precipitates when returned to neutral pH conditions. The midgut pH of susceptible beetle larvae is neutral to slightly acidic, a pH environment in which the Cry3A toxin is insoluble. To investigate this paradox we studied the Cry3A toxin after various proteolytic treatments. In many cases the toxin was cleaved into polypeptides that remained associated under non-denaturing conditions. Interestingly a chymotrypsinized Cry3A product was soluble under neutral pH conditions, retained full activity against susceptible beetle larvae, and exhibited specific binding to Leptinotarsa decemlineata midgut membranes.
由苏云金芽孢杆菌十斑亚种合成的Cry3A δ-内毒素蛋白包涵体可溶于碱性和酸性缓冲溶液，但当恢复到中性pH条件时，毒素会沉淀。易感甲虫幼虫的中肠pH呈中性至微酸性，在这种pH环境下Cry3A毒素不溶。为了研究这一矛盾现象，我们对Cry3A毒素进行了各种蛋白水解处理后进行了研究。在许多情况下，毒素被切割成在非变性条件下仍保持结合状态的多肽。有趣的是，经胰凝乳蛋白酶处理的Cry3A产物在中性pH条件下可溶，对易感甲虫幼虫保持完全活性，并与马铃薯甲虫中肠膜表现出特异性结合。
