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Structural basis for the unfolding of anthrax lethal factor by protective antigen oligomers

Nature Structural & Molecular Biology volume 17, pages 1383–1390 (2010)Cite this article

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Abstract

The protein transporter anthrax lethal toxin is composed of protective antigen (PA), a transmembrane translocase, and lethal factor (LF), a cytotoxic enzyme. After its assembly into holotoxin complexes, PA forms an oligomeric channel that unfolds LF and translocates it into the host cell. We report the crystal structure of the core of a lethal toxin complex to 3.1-Å resolution; the structure contains a PA octamer bound to four LF PA-binding domains (LFN). The first α-helix and β-strand of each LFN unfold and dock into a deep amphipathic cleft on the surface of the PA octamer, which we call the α clamp. The α clamp possesses nonspecific polypeptide binding activity and is functionally relevant to efficient holotoxin assembly, PA octamer formation, and LF unfolding and translocation. This structure provides insight into the mechanism of translocation-coupled protein unfolding.

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Figure 1: Structure of LF's PA-binding domain in complex with the PA octamer.
Figure 2: LFN electron density in the PA8(LFN)4 complex.
Figure 3: The PA octamer binds LFN in two distinct subsites.
Figure 4: Dynamics and thermodynamics of the pre-translocation unfolding of LFN.
Figure 5: The role of the α-clamp in LFN and LF translocation.

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Acknowledgements

We thank H. Gong, E. Haddadian, T. Sosnick and K. Freed for assistance in refining the backbone torsional angles using their unpublished TOP algorithm; J. Colby for assistance in purifying constructs; M. Brown for constructing the pET15-LFN-SalI vector; J. Berger and N. Echols for advice on crystallography; R. Zalpuri at the Robert D. Ogg Electron Microscope Laboratory; J. Holton and G. Meigs at the 8.3.1 beamline of the Advanced Light Source; and T. Sosnick, J. Collier, J. Berger and J. Kuriyan for helpful advice. This work was supported by University of California start-up funds (B.A.K.) and US National Institutes of Health research grants R01-AI077703 (B.A.K.) and R01-GM064712 (E.R.W.).

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Author notes

  1. Geoffrey K Feld and Katie L Thoren: These authors contributed equally to this work.

Authors and Affiliations

  1. Department of Chemistry, University of California, Berkeley, California, USA

    Geoffrey K Feld, Katie L Thoren, Alexander F Kintzer, Harry J Sterling, Iok I Tang, Evan R Williams & Bryan A Krantz

  2. Department of Molecular & Cell Biology, University of California, Berkeley, California, USA

    Shoshana G Greenberg & Bryan A Krantz

  3. California Institute for Quantitative Biosciences, University of California, Berkeley, California, USA

    Evan R Williams & Bryan A Krantz

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Contributions

G.K.F. crystallized, solved and refined the PA8(LFN)4 structure. G.K.F., K.L.T., H.J.S., A.F.K., S.G.G. and I.I.T. obtained functional data. G.K.F., K.L.T., H.J.S., A.F.K., E.R.W. and B.A.K. prepared the manuscript.

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Correspondence to Bryan A Krantz.

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Feld, G., Thoren, K., Kintzer, A. et al. Structural basis for the unfolding of anthrax lethal factor by protective antigen oligomers. Nat Struct Mol Biol 17, 1383–1390 (2010). https://doi.org/10.1038/nsmb.1923

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