Journal: J Virol / Year: 2007 Title: Infectious bursal disease virus capsid assembly and maturation by structural rearrangements of a transient molecular switch. Authors: Daniel Luque / Irene Saugar / José F Rodríguez / Nuria Verdaguer / Damiá Garriga / Carmen San Martín / Javier A Velázquez-Muriel / Benes L Trus / José L Carrascosa / José R Castón / Abstract: Infectious bursal disease virus (IBDV), a double-stranded RNA (dsRNA) virus belonging to the Birnaviridae family, is an economically important avian pathogen. The IBDV capsid is based on a single- ...Infectious bursal disease virus (IBDV), a double-stranded RNA (dsRNA) virus belonging to the Birnaviridae family, is an economically important avian pathogen. The IBDV capsid is based on a single-shelled T=13 lattice, and the only structural subunits are VP2 trimers. During capsid assembly, VP2 is synthesized as a protein precursor, called pVP2, whose 71-residue C-terminal end is proteolytically processed. The conformational flexibility of pVP2 is due to an amphipathic alpha-helix located at its C-terminal end. VP3, the other IBDV major structural protein that accomplishes numerous roles during the viral cycle, acts as a scaffolding protein required for assembly control. Here we address the molecular mechanism that defines the multimeric state of the capsid protein as hexamers or pentamers. We used a combination of three-dimensional cryo-electron microscopy maps at or close to subnanometer resolution with atomic models. Our studies suggest that the key polypeptide element, the C-terminal amphipathic alpha-helix, which acts as a transient conformational switch, is bound to the flexible VP2 C-terminal end. In addition, capsid protein oligomerization is also controlled by the progressive trimming of its C-terminal domain. The coordination of these molecular events correlates viral capsid assembly with different conformations of the amphipathic alpha-helix in the precursor capsid, as a five-alpha-helix bundle at the pentamers or an open star-like conformation at the hexamers. These results, reminiscent of the assembly pathway of positive single-stranded RNA viruses, such as nodavirus and tetravirus, add new insights into the evolutionary relationships of dsRNA viruses.
History
Deposition
Jul 11, 2006
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Header (metadata) release
Jul 11, 2006
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Map release
May 2, 2007
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Update
May 26, 2011
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Current status
May 26, 2011
Processing site: PDBe / Status: Released
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Structure visualization
Movie
Surface view with section colored by density value
Shell ID: 1 / Name: IBDV / Diameter: 700 Å / T number (triangulation number): 13
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Experimental details
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Structure determination
Method
negative staining, cryo EM
Processing
single particle reconstruction
Aggregation state
particle
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Sample preparation
Buffer
pH: 6.2 / Details: 25 mM PIPES, 150 mM NaCl, and 20 mM CaCl2
Staining
Type: NEGATIVE Details: Samples containing were applied to one side of a holey carbon film, washed twice on water drops, blotted, and plunged into a liquid ethane bath following standard procedures
Grid
Details: 300 mesh holey carbon film
Vitrification
Cryogen name: ETHANE
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Electron microscopy
Microscope
FEI TECNAI 20
Image recording
Digitization - Scanner: ZEISS SCAI / Digitization - Sampling interval: 7 µm / Number real images: 129 / Bits/pixel: 8
Electron beam
Acceleration voltage: 200 kV / Electron source: FIELD EMISSION GUN
Electron optics
Illumination mode: FLOOD BEAM / Imaging mode: BRIGHT FIELD
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