Daniell Sarah J, Kocsis Eva, Morris Edward, Knutton Stuart, Booy Frank P, Frankel Gad
Centre for Molecular Microbiology and Infection, Department of Biological Sciences, Imperial College, London, SW7 2AZ, UK.
Mol Microbiol. 2003 Jul;49(2):301-8. doi: 10.1046/j.1365-2958.2003.03555.x.
The type III secretion system (TTSS) is a modular apparatus assembled by many pathogenic Gram-negative bacteria and is designed to translocate proteins through the bacterial cell wall into the eukaryotic host cell. The conserved components of the TTSS comprise stacks of rings spanning the inner and outer bacterial membrane and a narrow, needle-like structure projecting outwards. The TTSS of enteropathogenic E. coli is unique in that one of the translocator proteins, EspA, polymerizes to form an extension to the needle complex which interacts with the host cell. In this study we present the 3D structure of EspA filaments to c. 26 A resolution determined from electron micrographs of negatively stained preparations by image processing. The structure comprises a helical tube with a diameter of 120 A enclosing a central channel of 25 A diameter through which effector proteins may be transported. The subunit arrangement corresponds to a one-start helix with 28 subunits present in five turns of the helix and an axial rise of 4.6 A per subunit. This is the first report of a 3D structure of a filamentous extension to the TTSS.
III型分泌系统（TTSS）是一种由许多致病性革兰氏阴性菌组装而成的模块化装置，旨在将蛋白质通过细菌细胞壁转运到真核宿主细胞中。TTSS的保守组件包括横跨细菌内膜和外膜的多环结构，以及向外突出的狭窄针状结构。肠致病性大肠杆菌的TTSS独特之处在于，其中一种转运蛋白EspA会聚合形成针状复合物的延伸部分，该延伸部分与宿主细胞相互作用。在本研究中，我们通过图像处理，从负染制剂的电子显微照片中确定了EspA细丝的三维结构，分辨率约为26埃。该结构由一个直径为120埃的螺旋管组成，包围着一个直径为25埃的中央通道，效应蛋白可能通过该通道运输。亚基排列对应于单起始螺旋，螺旋的五圈中有28个亚基，每个亚基的轴向上升为4.6埃。这是关于TTSS丝状延伸部分三维结构的首次报道。
