Electron cryo-microscopy of bacteriophage PR772 reveals the elusive vertex complex and the capsid architecture

Hemanth Kn Reddy,Janos Hajdu,Marta Carroni,Martin Svenda

doi:10.7554/elife.48496

Hemanth Kn Reddy, Janos Hajdu + Show 2 more

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https://doi.org/10.7554/elife.48496

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Abstract

Bacteriophage PR772, a member of the Tectiviridae family, has a 70 nm diameter icosahedral protein capsid that encapsulates a lipid membrane, dsDNA, and various internal proteins. An icosahedrally averaged CryoEM reconstruction of the wild-type virion and a localized reconstruction of the vertex region reveal the composition and the structure of the vertex complex along with new protein conformations that play a vital role in maintaining the capsid architecture of the virion. The overall resolution of the virion is 2.75 Å, while the resolution of the protein capsid is 2.3 Å. The conventional penta-symmetron formed by the capsomeres is replaced by a large vertex complex in the pseudo T = 25 capsid. All the vertices contain the host-recognition protein, P5; two of these vertices show the presence of the receptor-binding protein, P2. The 3D structure of the vertex complex shows interactions with the viral membrane, indicating a possible mechanism for viral infection.

Highlights

Bacteriophage PR772 is a double-stranded DNA virus with a 70 nm icosahedral protein capsid encapsulating the internal lipid bilayer along with numerous proteins and a 15 kbp long linear genome
In previous studies on PRD1, a close relative of PR772, it was shown that the capsid is formed by proteins P3, P30 and the vertex complex
The overall resolution determined by Fourier shell correlation (FSC) @0.143 was 2.75 Å (Figure 1–figure supplement 1)

Summary

Introduction

Bacteriophage PR772 is a double-stranded DNA (dsDNA) virus with a 70 nm icosahedral protein capsid encapsulating the internal lipid bilayer along with numerous proteins and a 15 kbp long linear genome It belongs to the Tectiviridae family and infects gram negative hosts like Escherichia coli, Salmonella typhimurium and other bacteria, carrying a R772 plasmid-encoded receptor complex through which DNA can be transported during bacterial conjugation 71 In previous studies on bacteriophage PRD1, a very close relative to PR772 from the Tectiviridae family, many models have been proposed to explain the architecture of the penton base and the vertex complex (Huiskonen, Manole, & Butcher, 2007; Javier Caldentey, Roman Tuma, & Bamford, 2000; Rydman et al, 1999; Sokolova et al, 2001). A combination of high-resolution icosahedral symmetrized single-particle reconstruction and localized asymmetric reconstruction has enabled us to answer some of the intriguing questions about the particle architecture, composition of the penton base and arrangement of the vertex complex

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