期刊
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
卷 113, 期 41, 页码 11519-11524出版社
NATL ACAD SCIENCES
DOI: 10.1073/pnas.1609482113
关键词
single-particle cryo-EM; Allolevivirus; ssRNA virus; genomic RNA; maturation protein
资金
- NIH [P41GM103832, U24GM116787]
- Department of Biochemistry and Biophysics at Texas AM University
- Public Health Service Grant [GM27099]
- Center for Phage Technology - Texas AgriLife
- Center for Phage Technology - Texas AM University
- Welch Foundation Grant [A-1863]
Single-stranded (ss) RNA viruses infect all domains of life. To date, for most ssRNA virions, only the structures of the capsids and their associated protein components have been resolved to high resolution. Q beta, an ssRNA phage specific for the conjugative F-pilus, has a T = 3 icosahedral lattice of coat proteins assembled around its 4,217 nucleotides of genomic RNA (gRNA). In the mature virion, the maturation protein, A(2), binds to the gRNA and is required for adsorption to the F-pilus. Here, we report the cryo-electron microscopy (cryo-EM) structures of Q beta with and without symmetry applied. The icosahedral structure, at 7-angstrom resolution, resolves loops not previously seen in the published X-ray structure, whereas the asymmetric structure, at 7-angstrom resolution, reveals A2 and the gRNA. A(2) contains a bundle of a-helices and replaces one dimer of coat proteins at a twofold axis. The helix bundle binds gRNA, causing denser packing of RNA in its proximity, which asymmetrically expands the surrounding coat protein shell to potentially facilitate RNA release during infection. We observe a fixed pattern of gRNA organization among all viral particles, with the major and minor grooves of RNA helices clearly visible. A single layer of RNA directly contacts every copy of the coat protein, with one-third of the interactions occurring at operator-like RNA hairpins. These RNA-coat interactions stabilize the tertiary structure of gRNA within the virion, which could further provide a roadmap for capsid assembly.
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