X-ray crystallography and EPR spectroscopy establish the mechanism of pilus formation in E. coli

The ability of bacteria to cause diseases depends, among other things, on their ability to stick to their host in order to be able to establish an infection. Many kinds of bacteria do this with the help of very thin protein hairs, known as pili. Like our hairs, these pili grow from the root. In a study published in the journal Nature, researchers at the Institute of Structural and Molecular Biology and the LCN, led by Professor Gabriel Waksman, have established the detailed structure of a complex involving the outermost, "sticky" FimH subunit of an E. coli pilus, as it is being exported through the outer membrane by a specialised protein export machine (the FimD usher) and still being guarded by a chaperone, FimC. The structure, which was obtained by X-ray crystallography augmented with EPR spectroscopy, shows the pilus tip protein lined up inside a hollow cylindrical channel of the usher protein. This is the first time that the structure of a complete protein export machine, including the actual protein to be exported, has been determined.

Dr Chris Kay, who led the EPR effort on the study, commented that the pulsed EPR approach using nitroxide spin labels to determine intra-molecular distances in proteins has now come of age as an important biophysical method to complement structural determinations by X-ray crystallography.

Further details can be found on the ISMB website http://www.ismb.lon.ac.uk/news.html and at on the Nature website at http://www.nature.com/nature/journal/v474/n7349/full/nature10109.html

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