Structure of a type III secretion needle at 7-Å resolution provides insights into its assembly and signaling mechanisms
Structure of a type III secretion needle at 7-Å resolution provides insights into its assembly and signaling mechanisms
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DOI：
10.1073/pnas.1116126109
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发表时间：
2012-03-20
影响因子：
11.1
通讯作者：
Namba, Keiichi
中科院分区：
文献类型：
--
作者：
Fujii, Takashi;Cheung, Martin;Namba, Keiichi
革兰氏阴性菌的III型分泌系统形成注射装置，在感染期间将效应蛋白输送到真核细胞中。它们跨越细菌膜和细胞外空间与宿主细胞质膜连接。它们的细胞外部分是一个针状的中空管，作为效应蛋白的分泌管道。福氏志贺氏菌的针长约50纳米，厚约7纳米，由一种蛋白质MxiH的螺旋组装而成。我们通过电子冷冻显微镜提供了志贺氏菌针的7埃分辨率3D图像重建，该图像分解了在针蛋白（包括MxiH）的晶体和溶液结构中从未观察到的α -螺旋和β -发夹。基于3d密度图的针的原子模型，与细菌鞭毛细丝的原子模型相比，提供了这样一个薄管结构是如何通过复杂的分子间相互作用稳定组装的见解。该图谱还阐明了针长控制蛋白如何在MxiH输出过程中作为中央通道中的标尺在针的远端组装，以及分泌激活信号如何通过宿主细胞接触时针的构象变化进行转导。
Type III secretion systems of Gram-negative bacteria form injection devices that deliver effector proteins into eukaryotic cells during infection. They span both bacterial membranes and the extracellular space to connect with the host cell plasma membrane. Their extracellular portion is a needle-like, hollow tube that serves as a secretion conduit for effector proteins. The needle of Shigella flexneri is approximately 50-nm long and 7-nm thick and is made by the helical assembly of one protein, MxiH. We provide a 7-angstrom resolution 3D image reconstruction of the Shigella needle by electron cryomicroscopy, which resolves alpha-helices and a beta-hairpin that has never been observed in the crystal and solution structures of needle proteins, including MxiH. An atomic model of the needle based on the 3D-density map, in comparison with that of the bacterial-flagellar filament, provides insights into how such a thin tubular structure is stably assembled by intricate intermolecular interactions. The map also illuminates how the needle-length control protein functions as a ruler within the central channel during export of MxiH for assembly at the distal end of the needle, and how the secretion-activation signal may be transduced through a conformational change of the needle upon host-cell contact.