Structural analysis of the Saf pilus by electron microscopy and image processing.

TitleStructural analysis of the Saf pilus by electron microscopy and image processing.
Publication TypeJournal Article
Year of Publication2008
AuthorsSalih, O., H. Remaut, G. Waksman, and E. V. Orlova
JournalJ Mol Biol
Volume379
Issue1
Pagination174-87
Date Published2008 May 23
Type of Articlesmm
ISSN1089-8638
KeywordsBacterial Proteins, Crystallography, X-Ray, Fimbriae, Bacterial, Image Processing, Computer-Assisted, Microscopy, Electron, Molecular Chaperones, Salmonella typhimurium
Abstract

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.

DOI10.1016/j.jmb.2008.03.056
Alternate JournalJ. Mol. Biol.
PubMed ID18448124
Grant List58149 / / Medical Research Council / United Kingdom
AI49950 / AI / NIAID NIH HHS / United States