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Structural characterization of a type III secretion system filament protein in complex with its chaperone

Nature Structural & Molecular Biology volume 12, pages 75–81 (2005)Cite this article

Abstract

The type III secretion system (TTSS) mediates the specific translocation of bacterial proteins into the cytoplasm of eukaryotic cells, a process essential for the virulence of many Gram-negative pathogens. The enteropathogenic Escherichia coli TTSS protein EspA forms a hollow extracellular filament believed to be a molecular conduit for type III protein translocation. Structural analysis of EspA has been hampered by its polymeric nature. We show that EspA alone is sufficient to form filamentous structures in the absence of other pathogenicity island–encoded proteins. CesA is the recently proposed chaperone of EspA, and we demonstrate that CesA traps EspA in a monomeric state and inhibits its polymerization. Crystallographic analysis of the heterodimeric CesA–EspA complex at a resolution of 2.8 Å reveals that EspA contains two long a-helices, which are involved in extensive coiled-coil interactions with CesA.

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Figure 1: CesA is dimeric and helical.
Figure 2: Purified EspA exists as filamentous oligomers.
Figure 3: CesA traps the EspA monomer.
Figure 4: Overall structure of the CesA–EspA complex in comparison with other secretion chaperones.
Figure 5: Interaction interface between CesA and EspA.

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Acknowledgements

We thank A.L. Lovering, M.G. Bertero, D. Lim, and P.I. Lario for assistance in data collection and analyses, R.A. Pfuetzner for assistance in multiangle light scattering, S. He for mass spectrometry service, G. Martens and E. Humphries for assistance in transmission EM, N.A. Thomas and W. Deng for advice and support and F. Rosell for assistance in CD spectroscopy. We thank the US Department of Energy and the staff at the Advanced Light Source beamline 8.2.2 for access and assistance in data collection. C.K. Yip is supported by training awards from the Natural Sciences and Engineering Research Council of Canada and the Michael Smith Foundation for Health Research. N.C.J. Strynadka thanks the Canadian Institutes of Health Research, Howard Hughes Medical Institute and Canadian Bacterial Diseases Network for financial support for this project.

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  1. Department of Biochemistry and Molecular Biology, University of British Columbia, 2146 Health Sciences Mall, Vancouver, V6T 1Z3, British Columbia, Canada

    Calvin K Yip & Natalie C J Strynadka

  2. Biotechnology Laboratory, University of British Columbia, Room 237, 6174 University Boulevard, Vancouver, V6T 1Z3, British Columbia, Canada

    B Brett Finlay

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Correspondence to Natalie C J Strynadka.

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Yip, C., Finlay, B. & Strynadka, N. Structural characterization of a type III secretion system filament protein in complex with its chaperone. Nat Struct Mol Biol 12, 75–81 (2005). https://doi.org/10.1038/nsmb879

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