Structural characterisation of the insecticidal toxin XptA1, reveals a 1.15 MDa tetramer with a cage-like structure
Structural characterisation of the insecticidal toxin XptA1, reveals a 1.15 MDa tetramer with a cage-like structure
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DOI：
10.1016/j.jmb.2006.12.057
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发表时间：
2007-03-09
影响因子：
5.6
通讯作者：
Morgan, J. Alun W.
中科院分区：
文献类型：
--
作者：
Lee, Sarah C.;Stoilova-Mcphie, Svetla;Morgan, J. Alun W.
最近鉴定的一类赋予肠杆菌科内的几种细菌杀虫活性的蛋白质具有控制商业上重要的昆虫害虫的潜力。在这里，我们报告的第一个纯化，生物物理表征。以及对来自嗜热短杆菌PMF 1296的毒素组分之一XptA 1的三维结构分析，分辨率为23 A。膜结合研究表明，三组分毒素系统具有不同的作用模式，从苏云金芽孢杆菌（Bt）的蛋白质。XptA 1的生物物理特性表明XptA 1的作用机制，即它首先与细胞膜结合，形成具有中央空腔的结构，并与其配偶体XptB 1和XptC 1形成复合物，产生完整的杀虫毒素。结合电子显微镜、超离心和圆二色性光谱分析，表明XptA 1是一个分子量为1.15 MDa的笼状四聚体。四个与螺旋相关的亚基中的每一个都具有三个明确定义的结构域和一端比另一端窄的纵向扭曲。XptA 1的三分之一的残基是α-螺旋的，这表明亚基通过α-螺旋卷曲螺旋相互作用部分关联。XptA 1本身在中性pH和碱性环境（pH 10.5）下显示出相同的二级结构。这种pH耐受性表明折叠的XptA 1可以通过对杀虫毒素复合物敏感的鳞翅目昆虫的中肠。因此，这意味着其折叠结构对其生物活性很重要。(c)2007爱思唯尔有限公司保留所有权利。
A recently identified class of proteins conferring insecticidal activity to several bacteria within the Enterobacteriaceae family have potential for control of commercially important insect pests. Here, we report the first purification, biophysical characterisation. and 3-D structural analysis of one of the toxin components, XptA1, from Xenorhabdus nematophila PMF1296 to a resolution of 23 A. Membrane binding studies indicate that the three-component toxin system has a different mode of action from that of proteins from Bacillus thuringiensis (Bt). Biophysical characterisation of XptA1 suggests a mechanism of action of XptA1 whereby it first binds to the cell membrane forming a structure with a central cavity and forms a complex with its partners XptB1 and XptC1 producing the full insecticidal toxin. The structure of XptA1 is shown by a combination of electron microscopy, ultracentrifugation and circular dichroism spectroscopy to be a 1.15 MDa tetramer with a cage-like structure. Each of the four symmetry-related subunits has three well-defined domains and a longitudinal twist with one end narrower than the other. One third of the residues of XptA1 are alpha-helical and it is suggested the subunits associate partly via an alpha-helical coiled-coil interaction. XptA1 itself shows the same secondary structure at neutral pH and in an alkaline environment up to pH10.5. This pH tolerance indicates that the folded XptA1 can pass through the midgut of Lepidopteran insects susceptible to the insecticidal toxin complex. This implies therefore that its folded structure is important for its biological activity. (c) 2007 Elsevier Ltd. All rights reserved.