Chan S W, Thanabalu T, Wee B Y, Porter A G
Institute of Molecular and Cell Biology, National University of Singapore, 10 Kent Ridge Crescent, Singapore 119260, Republic of Singapore.
J Biol Chem. 1996 Jun 14;271(24):14183-7. doi: 10.1074/jbc.271.24.14183.
Five different mosquitocidal toxin (mtx2) gene homologs have been cloned from eight Bacillus sphaericus strains. Pairwise comparisons of the predicted amino acid sequences show between four and eight substitutions compared with the prototype Mtx2 from B. sphaericus strain SSII-1. Mtx2 from strain SSII-1 was approximately 7-fold more toxic to Culex mosquito larvae than the Mtx2 homolog from B. sphaericus strain 31-2. Conversely, Mtx2 from strain 31-2 was approximately 100-fold more toxic to Aedes mosquito larvae than Mtx2 from strain SSII-1. Lys224 in Mtx2 was found to be the most important amino acid for toxicity to Culex larvae, and substitution of Lys224 with threonine abolished the toxicity of Mtx2 from strain SSII-1 to these larvae. In complete contrast, Thr224 was found to be crucial for the toxicity of Mtx2 from strain 31-2 to Aedes larvae, and substitution of Thr224 with lysine caused a approximately 100-fold drop in toxicity to these larvae. Thus, amino acid 224 in the Mtx2 family of mosquitocidal toxins is an unusual and important determinant of mosquito larvicidal activity and host range.
已从8株球形芽孢杆菌菌株中克隆出5种不同的杀蚊毒素（mtx2）基因同源物。对预测的氨基酸序列进行两两比较发现，与球形芽孢杆菌菌株SSII-1的原型Mtx2相比，存在4至8个氨基酸替换。菌株SSII-1的Mtx2对库蚊幼虫的毒性比球形芽孢杆菌菌株31-2的Mtx2同源物高约7倍。相反，菌株31-2的Mtx2对伊蚊幼虫的毒性比菌株SSII-1的Mtx2高约100倍。发现Mtx2中的赖氨酸224是对库蚊幼虫毒性最重要的氨基酸，用苏氨酸替换赖氨酸224会消除菌株SSII-1的Mtx2对这些幼虫的毒性。与此形成完全对比的是，发现苏氨酸224对菌株31-2的Mtx2对伊蚊幼虫的毒性至关重要，用赖氨酸替换苏氨酸224会导致对这些幼虫的毒性下降约100倍。因此，杀蚊毒素Mtx2家族中的第224位氨基酸是蚊幼虫icidal活性和宿主范围的一个不寻常且重要的决定因素。
