The bacteriophage t7 virion undergoes extensive structural remodeling during infection - PubMed (original) (raw)

The bacteriophage t7 virion undergoes extensive structural remodeling during infection

Bo Hu et al. Science. 2013.

Abstract

Adsorption and genome ejection are fundamental to the bacteriophage life cycle, yet their molecular mechanisms are not well understood. We used cryo-electron tomography to capture T7 virions at successive stages of infection of Escherichia coli minicells at ~4-nm resolution. The six phage tail fibers were folded against the capsid, extending and orienting symmetrically only after productive adsorption to the host cell surface. Receptor binding by the tail triggered conformational changes resulting in the insertion of an extended tail, which functions as the DNA ejection conduit into the cell cytoplasm. After ejection, the extended phage tail collapsed or disassembled, which allowed resealing of the infected cell membrane. These structural studies provide a detailed series of intermediates during phage infection.

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Figures

Fig. 1

Fig. 1

Three stages of T7 infection. (A and D) T7 adsorbed to the outer membrane. The density spanning the cell envelope at 270° in (A) was derived from fiducial gold markers (shown explicitly in movie S1 as a series of slices across the cell in (A). (B and E) An extended tail (arrow) spanned the cell envelope. (C and F) After DNA ejection, the extended tail was not apparent.

Fig. 2

Fig. 2

Asymmetric reconstructions of virions. (A) A central slice of a fiberless virion revealed the tail, capsid, and internal core. Fibers were visible in a central slice (B) and a cross section of wild-type virions (C). Surface rendering of fiberless (D) and wild-type virions in side (E) and bottom (F) views. A crystal structure of the receptor-binding domain of T7 fibers (5) was placed into three fiber densities. Residues A518, D520, and V544, known to affect phage host range (5), are highlighted in red (F). Classification revealed different conformations of fibers not bound (G) or bound to the capsid (H and I). (J) Distribution of the number of bound fibers on free virions; few had either six or zero fibers bound.

Fig. 3

Fig. 3

Adsorption structures. (A) Central slice and (B) 3D surface view of a subvolume average derived from 3352 virions. All six fibers were bound to the cell, and the tail made a small indentation in the outer membrane (OM); the internal core and DNA were still in the capsid. (C) Central slice and (D) 3D surface view of a subvolume average derived from 1886 virions. The internal core had been ejected from the virion, forming an extended tail that penetrated the cell cytoplasm. PG, peptidoglycan cell wall; IM, inner membrane.

Fig. 4

Fig. 4

Schematic model of T7 infection. The insert tomograms show the different orientations of tail fibers. Fibers bound to the cell are highlighted with yellow arrows, unbound fibers with green arrows. After “walking” across the cell surface to find the receptor for the tail, all fibers rotate downward to contact the outer membrane. Commitment to infection occurs after internal core proteins are ejected from the virion and the extended tail (red arrow) forms.

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References

    1. Johnson JE, Chiu W. Curr Opin Struct Biol. 2007;17:237. - PubMed
    1. Casjens SR, Molineux IJ. Adv Exp Med Biol. 2012;726:143. - PubMed
    1. Agirrezabala X, et al. EMBO J. 2005;24:3820. - PMC - PubMed
    1. Steven AC, et al. J Mol Biol. 1988;200:351. - PubMed
    1. Garcia-Doval C, van Raaij MJ. Proc Natl Acad Sci U S A. 2012;109:9390. - PMC - PubMed

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