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The structure of a cytolytic α-helical toxin pore reveals its assembly mechanism

Nature volume 459, pages 726–730 (2009)Cite this article

Abstract

Pore-forming toxins (PFTs) are a class of potent virulence factors that convert from a soluble form to a membrane-integrated pore1. They exhibit their toxic effect either by destruction of the membrane permeability barrier or by delivery of toxic components through the pores. Among the group of bacterial PFTs are some of the most dangerous toxins, such as diphtheria and anthrax toxin. Examples of eukaryotic PFTs are perforin and the membrane-attack complex, proteins of the immune system2. PFTs can be subdivided into two classes, α-PFTs and β-PFTs, depending on the suspected mode of membrane integration, either by α-helical or β-sheet elements3. The only high-resolution structure of a transmembrane PFT pore is available for a β-PFT—α-haemolysin from Staphylococcus aureus4. Cytolysin A (ClyA, also known as HlyE), an α-PFT, is a cytolytic α-helical toxin responsible for the haemolytic phenotype of several Escherichia coli and Salmonella enterica strains5,6,7,8. ClyA is cytotoxic towards cultured mammalian cells, induces apoptosis of macrophages and promotes tissue pervasion9,10,11. Electron microscopic reconstructions demonstrated that the soluble monomer of ClyA12 must undergo large conformational changes to form the transmembrane pore13,14. Here we report the 3.3 Å crystal structure of the 400 kDa dodecameric transmembrane pore formed by ClyA. The tertiary structure of ClyA protomers in the pore is substantially different from that in the soluble monomer. The conversion involves more than half of all residues. It results in large rearrangements, up to 140 Å, of parts of the monomer, reorganization of the hydrophobic core, and transitions of β-sheets and loop regions to α-helices. The large extent of interdependent conformational changes indicates a sequential mechanism for membrane insertion and pore formation.

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Figure 1: Structure of the ClyA pore.
Figure 2: Conformational differences between the soluble and the protomeric form.
Figure 3: Key residues for triggering the conformational switch.
Figure 4: Mechanism of pore formation.

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Accession codes

Primary accessions

Protein Data Bank

Data deposits

Atomic coordinates and structure factors for the ClyA-pore have been deposited in the PDB data bank under accession number 2WCD.

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Acknowledgements

We thank B. Blattmann for help with initial screening, N. Eifler and A. Engel for providing electron microscopy maps, D. Boehringer for sample characterization, and H. Fäh-Rechsteiner for technical assistance. We also acknowledge the staff of X06SA at the Swiss Light Source for developing an excellent beamline and support with data collection, T. C. Terwilliger for his support using RESOLVE, and M. Leibundgut and D. Boehringer for critically reading the manuscript. This work was supported by the Swiss National Science Foundation (SNSF) and the National Center of Excellence in Research (NCCR) Structural Biology program of the SNSF.

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Author notes

  1. Marcus Mueller & Ulla Grauschopf

    Present address: Present addresses: Paul Scherrer Institut, 5232 Villigen PSI, Switzerland (M.M.); Formulation R&D Biologics, Pharmaceutical and Analytical R&D, F. Hoffmann-La Roche Ltd, 4070 Basel, Switzerland (U.G.).,

Authors and Affiliations

  1. Institute of Molecular Biology and Biophysics, ETH Zurich, 8093 Zurich, Switzerland ,

    Marcus Mueller, Ulla Grauschopf, Timm Maier, Rudi Glockshuber & Nenad Ban

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Correspondence to Nenad Ban.

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Mueller, M., Grauschopf, U., Maier, T. et al. The structure of a cytolytic α-helical toxin pore reveals its assembly mechanism. Nature 459, 726–730 (2009). https://doi.org/10.1038/nature08026

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