Structural and energetic basis of folded-protein transport by the FimD usher

Abstract

Type 1 pili, produced by uropathogenic Escherichia coli, are multisubunit fibres crucial in recognition of and adhesion to host tissues1. During pilus biogenesis, subunits are recruited to an outer membrane assembly platform, the FimD usher, which catalyses their polymerization and mediates pilus secretion2. The recent determination of the crystal structure of an initiation complex provided insight into the initiation step of pilus biogenesis resulting in pore activation, but very little is known about the elongation steps that follow3. Here, to address this question, we determine the structure of an elongation complex in which the tip complex assembly composed of FimC, FimF, FimG and FimH passes through FimD. This structure demonstrates the conformational changes required to prevent backsliding of the nascent pilus through the FimD pore and also reveals unexpected properties of the usher pore. We show that the circular binding interface between the pore lumen and the folded substrate participates in transport by defining a low-energy pathway along which the nascent pilus polymer is guided during secretion.

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Figure 1: Structure of FimD–FimC–FimF–FimG–FimH.
Figure 2: Comparison of the structures of FimH before and after translocation.
Figure 3: Steep energy funnels and opposing binding surfaces position the translocating substrate at the centre of the pore.
Figure 4: A low-energy pathway through the pore lumen facilitates translocation of subunits and their transfer from NTD to CTDs.

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Primary accessions

Protein Data Bank

Data deposits

The atomic coordinates and structure factors of FimD–FimC–FimF–FimG–FimH have been deposited in the Protein Data Bank under accession ID 4J3O.

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Acknowledgements

This work was funded by Medical Research Council grant 85602 to G.W. D.B. and E.P. are supported by grant P41 GM103533 from the National Institute of General Medical Studies at the US National Institutes of Health (NIH). S.J.H. was supported by grant AI029549 from the National Institute of Allergy and Infectious Disease at the NIH. We thank the staff of beamline ID23-1 at the European Synchrotron Radiation Facility, the staff of beamline IO2 at the Diamond Light source and A. Cole for technical assistance during data collection.

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S.G. and E.P. carried out the crystallographic and computational work, respectively. D.B. and G.W. supervised the work. S.G., E.P., D.B. and G.W. analysed the data. S.G., E.P., S.J.H., D.B. and G.W. wrote the paper.

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Correspondence to David Baker or Gabriel Waksman.

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The authors declare no competing financial interests.

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This file contains Supplementary Methods, Supplementary Tables 1-2, Supplementary Figures 1-16 and Supplementary References. (PDF 23699 kb)

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Geibel, S., Procko, E., Hultgren, S. et al. Structural and energetic basis of folded-protein transport by the FimD usher. Nature 496, 243–246 (2013). https://doi.org/10.1038/nature12007

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