Structural dynamics of bacteriophage P22 infection initiation revealed by cryo-electron tomography

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For successful infection, bacteriophages must overcome multiple barriers to transport their genome and proteins across the bacterial cell envelope. We use cryo-electron tomography to study the infection initiation of phage P22 in Salmonella enterica serovar Typhimurium, revealing how a channel forms to allow genome translocation into the cytoplasm. Our results show free phages that initially attach obliquely to the cell through interactions between the O antigen and two of the six tailspikes; the tail needle also abuts the cell surface. The virion then orients perpendicularly and the needle penetrates the outer membrane. The needle is released and the internal head protein gp7* is ejected and assembles into an extracellular channel that extends from the gp10 baseplate to the cell surface. A second protein, gp20, is ejected and assembles into a structure that extends the extracellular channel across the outer membrane into the periplasm. Insertion of the third ejected protein, gp16, into the cytoplasmic membrane probably completes the overall trans-envelope channel into the cytoplasm. Construction of a trans-envelope channel is an essential step during infection of Gram-negative bacteria by all short-tailed phages, because such virions cannot directly deliver their genome into the cell cytoplasm.

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Fig. 1: Tomograms reveal P22 intermediates at different stages of infection.
Fig. 2: P22 binds obliquely to the cell surface.
Fig. 3: Intermediate structures during commitment to infection.
Fig. 4: The 3D structure of the trans-envelope channel.
Fig. 5: Channel formed by E protein-defective particles.

Data availability

The structures derived from cryo-ET and subtomogram averaging were deposited in the Electron Microscopy Data Bank under accession codes EMDB-9006, EMDB-9007, EMDB-9008, EMDB-9009 and EMDB-9010.


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We thank S. Casjens for providing phage strains and amber mutant sequence data. We also thank M. M. Susskind and A. R. Poteete for phage and bacterial strains. This work was supported by grant nos. GM124378 and GM110243 to I.J.M. and J.L. C.W., J.T. and J.L. were also supported in part by grant no. AI087946 from the NIAID and grant no. AU-1714 from the Welch Foundation.

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J.L. and I.J.M. designed the research. C.W., J.T., I.J.M. and J.L. prepared the samples and collected and analysed the data. C.W., J.T., J.L. and I.J.M. wrote the manuscript.

Correspondence to Ian J. Molineux.

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Wang, C., Tu, J., Liu, J. et al. Structural dynamics of bacteriophage P22 infection initiation revealed by cryo-electron tomography. Nat Microbiol 4, 1049–1056 (2019) doi:10.1038/s41564-019-0403-z

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