Hahn E, Wild P, Schraner E M, Bertschinger H U, Häner M, Müller S A, Aebi U
Institute of Veterinary Anatomy, University of Zürich, CH-8057 Zürich, Switzerland.
J Struct Biol. 2000 Dec;132(3):241-50. doi: 10.1006/jsbi.2000.4323.
The F18 fimbriae expressed by porcine toxigenic Escherichia coli strains are 1- to 2-mm-long filaments that mediate the adhesion of the bacteria to enterocytes. The backbone of these fimbriae is built from a major structural 15.1-kDa protein, FedA. The structure of isolated negatively stained F18 fimbriae imaged by dark-field scanning transmission electron microscopy (STEM) was resolved to approximately 2 nm. Analyzing their helical symmetry showed the axially repeating units to alternate in a "zigzag" manner around the helical axis with an axial rise of 2.2 nm. Two repeating units give rise to the observed 4.3-nm helical repeat, which is practically identical to the pitch of the one-start helix formed. Additionally, an axially repeating pattern with a 27-nm spacing was found on rotary-shadowed fimbriae. Mass-per-length determination of unstained F18 fimbriae by STEM revealed the axially repeating unit to have a molecular mass of 25.4 kDa, indicating that it is a FedA monomer, with the difference in mass arising from the minor subunits, FedE and FedF. The presence of the latter two proteins might cause the observed 27-nm axial pattern.
猪产毒素大肠杆菌菌株表达的F18菌毛是1到2毫米长的细丝，介导细菌与肠上皮细胞的黏附。这些菌毛的主干由一种主要结构蛋白FedA（15.1 kDa）构成。通过暗场扫描透射电子显微镜（STEM）对分离的负染F18菌毛成像，其结构分辨率约为2纳米。分析其螺旋对称性表明，轴向重复单元围绕螺旋轴以“之字形”方式交替，轴向上升2.2纳米。两个重复单元产生了观察到的4.3纳米螺旋重复，这与形成的单起始螺旋的螺距几乎相同。此外，在旋转阴影的菌毛上发现了间距为27纳米的轴向重复模式。通过STEM对未染色的F18菌毛进行单位长度质量测定，结果显示轴向重复单元的分子量为25.4 kDa，表明它是一个FedA单体，质量差异源于次要亚基FedE和FedF。后两种蛋白质的存在可能导致观察到的27纳米轴向模式。
