Zhang Peijun, Khursigara Cezar M, Hartnell Lisa M, Subramaniam Sriram
Laboratory of Cell Biology, Center for Cancer Research, National Cancer Institute, National Institutes of Health, Bethesda, MD 20892, USA.
Proc Natl Acad Sci U S A. 2007 Mar 6;104(10):3777-81. doi: 10.1073/pnas.0610106104. Epub 2007 Feb 26.
Signal transduction in bacterial chemotaxis is initiated by the binding of extracellular ligands to a specialized family of methyl-accepting chemoreceptor proteins. Chemoreceptors cluster at distinct regions of the cell and form stable ternary complexes with the histidine autokinase CheA and the adapter protein CheW. Here we report the direct visualization and spatial organization of chemoreceptor arrays in intact Escherichia coli cells by using cryo-electron tomography and biochemical techniques. In wild-type cells, ternary complexes are arranged as an extended lattice, which may or may not be ordered, with significant variations in the size and specific location among cells in the same population. In the absence of CheA and CheW, chemoreceptors do not form observable clusters and are diffusely localized to the cell pole. At disproportionately high receptor levels, membrane invaginations containing nonfunctional, axially interacting receptor assemblies are formed. However, functional chemoreceptor arrays can be reestablished by increasing cellular levels of CheA and CheW. Our results demonstrate that chemotaxis in E. coli requires the presence of chemoreceptor arrays and that the formation of these arrays requires the scaffolding interactions of the signaling molecules CheA and CheW.
细菌趋化作用中的信号转导是由细胞外配体与一类特殊的甲基接受趋化受体蛋白结合引发的。趋化受体聚集在细胞的不同区域，并与组氨酸自激酶CheA和衔接蛋白CheW形成稳定的三元复合物。在此，我们通过冷冻电子断层扫描和生化技术报告了完整大肠杆菌细胞中趋化受体阵列的直接可视化和空间组织情况。在野生型细胞中，三元复合物排列成一个扩展的晶格结构，其可能有序也可能无序，同一群体中的细胞在大小和具体位置上存在显著差异。在没有CheA和CheW的情况下，趋化受体不会形成可观察到的簇，而是分散地定位于细胞极。在受体水平过高的情况下，会形成含有无功能的、轴向相互作用的受体组装体的膜内陷。然而，通过增加细胞内CheA和CheW的水平可以重新建立功能性趋化受体阵列。我们的结果表明，大肠杆菌中的趋化作用需要趋化受体阵列的存在，并且这些阵列的形成需要信号分子CheA和CheW的支架相互作用。
