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Donor-strand exchange in chaperone-assisted pilus assembly revealed in atomic detail by molecular dynamics

Paci, E., Rose, R.J., Welsh, T.S., Waksman, G., Ashcroft, A.E. and Radford, S.E. (2008) Donor-strand exchange in chaperone-assisted pilus assembly revealed in atomic detail by molecular dynamics. Journal of Molecular Biology, 375 (4). pp. 908-919. ISSN 0022-2836

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Adhesive multi-subunit fibres are assembled on the surface of many pathogenic bacteria via the chaperone-usher pathway. In the periplasm, a chaperone donates a β-strand to a pilus subunit to complement its incomplete immunoglobulin-like fold. At the outer membrane, this is replaced with a β-strand formed from the N-terminal extension (Nte) of an incoming pilus subunit by a donorstrand exchange (DSE) mechanism. This reaction has previously been shown to proceed via a concerted mechanism, in which the Nte interacts with the chaperone:subunit complex before the chaperone has been displaced, forming a ternary intermediate. Thereafter, the pilus and chaperone β-strands have been postulated to undergo a strand swap by a ‘zip-in-zip-out’ mechanism, whereby the chaperone strand zips out, residue by residue, as the Nte simultaneously zips in. Here, molecular dynamics simulations have been used to probe the DSE mechanism during formation of the Salmonella enterica Saf pilus at an atomic level, allowing the direct investigation of the zip-inzip- out hypothesis. The simulations provide an explanation of how the incoming Nte is able to dock and initiate DSE due to inherent dynamic fluctuations within the chaperone:subunit complex. The chaperone donor-strand is shown to unbind from the pilus subunit residue by residue, in direct support of the zip-in-zip-out hypothesis. In addition, an interaction of a residue towards the Nterminus of the Nte with a specific binding pocket (P*) on the adjacent pilus subunit is shown to stabilise the DSE product against unbinding, which also proceeds by a zippering mechanism. Together, the study provides an in-depth picture of DSE, including the first insights into the molecular events occurring during the zip-in-zip-out mechanism.

Item Type: Article
Copyright, Publisher and Additional Information: © 2008 Elsevier Science B.V, Amsterdam. This is an author produced version of a paper published in the Journal of Molecular Biology. Uploaded in accordance with the publisher's self archiving policy.
Keywords: Molecular dynamics, pili, chaperone, donor-strand exchange, assembly mechanisms
Institution: The University of Leeds
Academic Units: The University of Leeds > University of Leeds Research Centres and Institutes > Astbury Centre for Structural Molecular Biology (Leeds)
The University of Leeds > Faculty of Biological Sciences (Leeds) > School of Molecular and Cellular Biology (Leeds)
The University of Leeds > Faculty of Maths and Physical Sciences (Leeds) > School of Physics and Astronomy (Leeds)
Depositing User: Repository Administrator York
Date Deposited: 16 Apr 2008 18:27
Last Modified: 17 Aug 2015 13:36
Published Version: http://dx.doi.org/10.1016/j.jmb.2007.10.077
Status: Published
Publisher: Elsevier
Refereed: Yes
Identification Number: 10.1016/j.jmb.2007.10.077
Related URLs:
URI: http://eprints.whiterose.ac.uk/id/eprint/3662

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