PSI Structural Biology Knowledgebase

PSI | Structural Biology Knowledgebase
Header Icons
E-Collection

Related Articles
Protein Folding and Misfolding: It's the Journey, Not the Destination
March 2015
CCR5 and HIV Infection
January 2015
HIV/AIDS: Pre-fusion Env Exposed
January 2015
HIV/AIDS: Slide to Enter
January 2015
Updating ModBase
January 2015
Power in Numbers
August 2014
Quorum Sensing: A Groovy New Component
August 2014
Bacterial CDI Toxins
June 2014
Immunity: One Antibody to Rule Them All
June 2014
Virology: A Bat Influenza Hemagglutinin
March 2014
Virology: Making Sensitive Magic
March 2014
Virology: Visualizing Cyanophage Assembly
March 2014
Virology: Zeroing in on HBV Egress
March 2014
Viroporins
March 2014
Cas4 Nuclease and Bacterial Immunity
February 2014
Microbial Pathogenesis: A GNAT from Pseudomonas
February 2014
Microbial Pathogenesis: Targeting Drug Resistance in Mycobacterium tuberculosis
February 2014
Microbiome: The Dynamics of Infection
September 2013
Membrane Proteome: A Funnel-like Viroporin
August 2013
Infectious Diseases: A Pathogen Ubiquitin Ligase
May 2013
Infectious Diseases: A Shared Syringe
May 2013
Infectious Diseases: Determining the Essential Structome
May 2013
Infectious Diseases: Targeting Meningitis
May 2013
NDM-1 and Antibiotics
May 2013
Bacterial Hemophores
January 2013
Microbial Pathogenesis: Computational Epitope Prediction
January 2013
Microbial Pathogenesis: Influenza Inhibitor Screen
January 2013
Microbial Pathogenesis: Measles Virus Attachment
January 2013
Microbial Pathogenesis: NEAT Iron
January 2013
Membrane Proteome: Sphingolipid Synthesis Selectivity
December 2012
A signal sensing switch
September 2012
Gauging needle structure
July 2012
Anthrax Stealth Siderophores
June 2012
A Pseudomonas L-serine dehydrogenase
May 2012
Pilus Assembly Protein TadZ
April 2012
Making Lipopolysaccharide
January 2012
Superbugs and Antibiotic Resistance
December 2011
A change to resistance
November 2011
An effective and cooperative dimer
November 2011
The Perils of Protein Secretion
November 2011
Bacterial Armor
October 2011
Breaking down the defenses
September 2011
Moving some metal
August 2011
Capsid assembly in motion
April 2011
Know thy enemy … structurally
October 2010
Treating sleeping sickness
May 2010
Bacterial spore kinase
April 2010
Hemolysin BL
January 2010
Unusual cell division
October 2009
Anthrax evasion tactics
September 2009
Toxin-antitoxin VapBC-5
September 2009
Antibiotic target
August 2009
Lysostaphin
July 2009
Tackling influenza
June 2009
You look familiar: the Type VI secretion system
June 2009
Unique SARS
April 2009
Anthrax stealth molecule
March 2009
A new class of bacterial E3 ubiquitination enzymes
January 2009
Antiviral evasion
October 2008
SARS connections
September 2008
SARS Coronavirus Nonstructural Protein 1
June 2008

Research Themes Infectious diseases

Virology: Visualizing Cyanophage Assembly

SBKB [doi:10.1038/sbkb.2012.190]
Technical Highlight - March 2014
Short description: The first application of ZPC cryoET provides insight into cyanophage assembly process.

Annotated view of infected cell at intermediate stage of infection. 1

Cyanophages are double-stranded DNA viruses that infect a wide range of photosynthetic cyanobacteria. Using a new electron microscopy approach, Zernike phase contrast electron cryo-tomography (ZPC cryoET), Chiu and colleagues analyzed the assembly pathway of the cyanophage Syn5 in its natural host cells at nanometer resolution.

Synechococcus sp. strain WH8109 cells were frozen before and after infection, and imaged in an electron microscope equipped with a Zernike phase plate placed in the back focal plane of the objective lens. This substantially enhanced image contrast compared to conventional cryoET. The authors reconstructed 58 ZPC tomograms of the cells and classified 470 intracellular Syn5-like particles into three morphological types, which were further analyzed to obtain 50–70-Å resolution averages.

The largest population of particles resembles mature Syn5 phage, a short-tailed icosahedral capsid shell with a horn appendage at the vertex opposite the tail and an internal density that is attributed to DNA. Three particle subtypes were observed: those with a bulky tail and a slim horn appendage on opposing vertices, as in the mature phage; a tail at one vertex only; and without detectable density protruding from any vertex. This categorization suggests that the assembly of the tail hub follows DNA packaging, but precedes the addition of the horn.

The second phage population, thought to represent Syn5 procapsids, consists of spherical particles that are slightly smaller than mature Syn5, with a density extending inward at one location of the shell, which is interpreted to represent the Syn5 portal. The third particle type, expanded capsids, had not been previously reported and is similar to mature Syn5 in size and angular in shape, with the majority of particles displaying icosahedral symmetry. An internally protruding density is suggested to correspond to the full-length portal protein complex, whereas an external protruding density might represent the terminase.

By mapping the frequency of the three phage populations as infection progresses, procapsids and expanded capsids appear first, but disappear again as the population of DNA-containing capsids grows. Thus, the expanded capsids represent an intermediate state in the assembly process, and expansion and angularity of the protein shell are completed before the viral DNA is fully packaged. This morphogenetic assembly pathway resembles that of enteric bacteriophages and eukaryotic viruses, suggesting that it is highly conserved and likely inherited from cyanobacteria, which precede enteric bacteria in evolution.

Arianne Heinrichs

References

  1. W. Dai et al. Visualizing virus assembly intermediates inside marine cyanobacteria.
    Nature. 502, 707-710 (2014). doi:10.1038/nature12604

Structural Biology Knowledgebase ISSN: 1758-1338
Funded by a grant from the National Institute of General Medical Sciences of the National Institutes of Health