Cryo-EM structure in situ reveals a molecular switch that safeguards virus against genome loss
Abstract
The portal protein is a key component of many double-stranded DNA viruses, governing capsid assembly and genome packaging. Twelve subunits of the portal protein define a tunnel, through which DNA is translocated into the capsid. It is unknown how the portal protein functions as a gatekeeper, preventing DNA slippage, whilst allowing its passage into the capsid, and how these processes are controlled. A cryo-EM structure of the portal protein of thermostable virus P23-45, determined in situ in its procapsid-bound state, indicates a mechanism that naturally safeguards the virus against genome loss. This occurs via an inversion of the conformation of the loops that define the constriction in the central tunnel, accompanied by a hydrophilic–hydrophobic switch. The structure also shows how translocation of DNA into the capsid could be modulated by a changing mode of protein–protein interactions between portal and capsid, across a symmetry-mismatched interface.
Data availability
Cryo-EM reconstruction (EMD-4567) and atomic coordinates (PDB 6QJT) have been deposited with the wwPDB (www.wwpdb.org).
Article and author information
Author details
Funding
Wellcome (103460)
- Oliver W Bayfield
Wellcome (206377)
- Alfred A Antson
National Institute of Arthritis and Musculoskeletal and Skin Diseases (Intramural Research Program)
- Alasdair C Steven
The funders had no role in study design, data collection and interpretation, or the decision to submit the work for publication.
Copyright
This is an open-access article, free of all copyright, and may be freely reproduced, distributed, transmitted, modified, built upon, or otherwise used by anyone for any lawful purpose. The work is made available under the Creative Commons CC0 public domain dedication.
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