Dean D H, Rajamohan F, Lee M K, Wu S J, Chen X J, Alcantara E, Hussain S R
Department of Biochemistry, Ohio State University, Columbus, 43210, USA.
Gene. 1996 Nov 7;179(1):111-7. doi: 10.1016/s0378-1119(96)00442-8.
The current model of the mechanism of action of several Bacillus thuringiensis insecticidal crystal proteins (Cry) is reviewed and tested by site-directed mutagenesis experiments. Amino acid (aa) residues were substituted in each of the three domains of Cry toxins and the effects on toxin stability, binding to receptors, irreversible insertion into the membrane, and ion channel activity were examined. Mutant proteins with aa altered on the putative membrane-proximal surface of domain I are affected in insertion into the membrane and toxicity, but not in binding to the receptor. Alterations in the putative receptor-binding loops of domain II show an effect on the initial (reversible) binding to the receptor when certain aa are altered, while affecting irreversible binding when other aa are altered. Mutant proteins with aa altered in a conserved track of aa of domain III have altered ion channel properties, as measured by the voltage clamping of insect midguts and the K+ permeability of brush border membrane vesicles. In summary, domain I is involved in insertion into the membrane and affects ion channel function, domain II is involved in receptor binding and insertion into the membrane, and domain III is involved ion channel function, receptor binding, and insertion into the membrane.
本文回顾了几种苏云金芽孢杆菌杀虫晶体蛋白（Cry）作用机制的当前模型，并通过定点诱变实验进行了验证。在Cry毒素的三个结构域中分别替换氨基酸（aa）残基，并检测其对毒素稳定性、与受体结合、不可逆插入膜以及离子通道活性的影响。在结构域I假定的膜近端表面上改变aa的突变蛋白在插入膜和毒性方面受到影响，但在与受体结合方面不受影响。当某些aa发生改变时，结构域II假定的受体结合环的改变对与受体的初始（可逆）结合有影响，而当其他aa发生改变时则影响不可逆结合。通过对昆虫中肠进行电压钳制和测量刷状缘膜囊泡的K +通透性发现，在结构域III的保守aa序列中改变aa的突变蛋白具有改变的离子通道特性。总之，结构域I参与膜插入并影响离子通道功能，结构域II参与受体结合和膜插入，结构域III参与离子通道功能、受体结合和膜插入。
