Salih Osman, Remaut Han, Waksman Gabriel, Orlova Elena V
Institute of Structural Molecular Biology at UCL/Birkbeck, London WC1E 7HX, UK.
J Mol Biol. 2008 May 23;379(1):174-87. doi: 10.1016/j.jmb.2008.03.056. Epub 2008 Apr 3.
Bacterial pili are important virulence factors involved in host cell attachment and/or biofilm formation, key steps in establishing and maintaining successful infection. Here we studied Salmonella atypical fimbriae (or Saf pili), formed by the conserved chaperone/usher pathway. In contrast to the well-established quaternary structure of typical/FGS-chaperone assembled, rod-shaped, chaperone/usher pili, little is known about the supramolecular organisation in atypical/FGL-chaperone assembled fimbriae. In our study, we have used negative stain electron microscopy and single-particle image analysis to determine the three-dimensional structure of the Salmonella typhimurium Saf pilus. Our results show atypical/FGL-chaperone assembled fimbriae are composed of highly flexible linear multi-subunit fibres that are formed by globular subunits connected to each other by short links giving a "beads on a string"-like appearance. Quantitative fitting of the atomic structure of the SafA pilus subunit into the electron density maps, in combination with linker modelling and energy minimisation, has enabled analysis of subunit arrangement and intersubunit interactions in the Saf pilus. Short intersubunit linker regions provide the molecular basis for flexibility of the Saf pilus by acting as molecular hinges allowing a large range of movement between consecutive subunits in the fibre.
细菌菌毛是参与宿主细胞黏附和/或生物膜形成的重要毒力因子，是建立和维持成功感染的关键步骤。在此，我们研究了由保守的伴侣/组装途径形成的沙门氏菌非典型菌毛（或Saf菌毛）。与典型的/FGS伴侣组装的、杆状的、伴侣/组装菌毛的既定四级结构不同，对于非典型/FGL伴侣组装菌毛的超分子组织知之甚少。在我们的研究中，我们使用了负染电子显微镜和单颗粒图像分析来确定鼠伤寒沙门氏菌Saf菌毛的三维结构。我们的结果表明，非典型/FGL伴侣组装菌毛由高度灵活的线性多亚基纤维组成，这些纤维由球状亚基通过短连接相互连接形成，呈现出“串珠”状外观。将SafA菌毛亚基的原子结构定量拟合到电子密度图中，结合连接体建模和能量最小化，能够分析Saf菌毛中的亚基排列和亚基间相互作用。短的亚基间连接区域通过充当分子铰链，允许纤维中连续亚基之间进行大范围的运动，从而为Saf菌毛的灵活性提供了分子基础。
