Article | Published:

Extensive subunit contacts underpin herpesvirus capsid stability and interior-to-exterior allostery

Nature Structural & Molecular Biology volume 23, pages 531539 (2016) | Download Citation

Abstract

The herpesvirus capsid is a complex protein assembly that includes hundreds of copies of four major subunits and lesser numbers of several minor proteins, all of which are essential for infectivity. Cryo-electron microscopy is uniquely suited for studying interactions that govern the assembly and function of such large functional complexes. Here we report two high-quality capsid structures, from human herpes simplex virus type 1 (HSV-1) and the animal pseudorabies virus (PRV), imaged inside intact virions at ~7-Å resolution. From these, we developed a complete model of subunit and domain organization and identified extensive networks of subunit contacts that underpin capsid stability and form a pathway that may signal the completion of DNA packaging from the capsid interior to outer surface, thereby initiating nuclear egress. Differences in the folding and orientation of subunit domains between herpesvirus capsids suggest that common elements have been modified for specific functions.

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Acknowledgements

The authors thank K. Sader (FEI) for expert technical assistance with collecting the PRV data set, and H. Lopez, T. Neef, and J. Yoder for technical assistance in the early stages of image analysis. We gratefully acknowledge W. Busing and J. Balkovec of FEI for assisting with access to a Krios microscope for data collection, and R. Duda for his comments on the manuscript. J. Brown (University of Virginia) kindly provided an anti-pUL25 mouse monoclonal antibody, and J. Baines (Cornell University) provided an anti-pUL17 chicken polyclonal antibody. This work was supported by NIH grants R01AI089803 (J.F.C. and F.L.H.) and R56AI060836 (F.L.H.).

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Affiliations

  1. Department of Structural Biology, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania, USA.

    • Alexis Huet
    • , Alexander M Makhov
    •  & James F Conway
  2. Department of Microbiology and Molecular Genetics, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania, USA.

    • Jamie B Huffman
    •  & Fred L Homa
  3. Apps Lab, FEI Europe, Eindhoven, the Netherlands.

    • Matthijn Vos

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Contributions

J.F.C. and F.L.H. developed the concepts and experiments; J.B.H. and F.L.H. prepared samples and performed biochemistry; A.M.M. prepared grids; M.V. and J.F.C. developed microscopy procedures and collected data; A.H. and J.F.C. performed data analyses and interpretation; J.F.C., F.L.H. and A.H. prepared the manuscript, which was edited by A.M.M. and M.V.

Competing interests

The authors declare no competing financial interests.

Corresponding author

Correspondence to James F Conway.

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    Supplementary Text and Figures

    Supplementary Figures 1–5

  2. 2.

    Supplementary Data Set 1

    Complete western blots and SDS–PAGE used in Figure 6

Videos

  1. 1.

    View of the herpesvirus capsid reconstruction

    A surface view of the HSV-1 capsid density map is shown from the exterior, and as elements, including the triplex density from the exterior and interior, and a VP5 subunit from a hexon. The movie ends with a zoomed-in view showing the HK97-based fold (red) fit into the green surface of the lower domain (green).

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DOI

https://doi.org/10.1038/nsmb.3212

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