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Journal of Virology, July 2007, p. 6869-6878, Vol. 81, No. 13
0022-538X/07/$08.00+0     doi:10.1128/JVI.00077-07
Copyright © 2007, American Society for Microbiology. All Rights Reserved.

Infectious Bursal Disease Virus Capsid Assembly and Maturation by Structural Rearrangements of a Transient Molecular Switch{triangledown}

Daniel Luque,1 Irene Saugar,1,{dagger} José F. Rodríguez,2 Nuria Verdaguer,3 Damiá Garriga,3 Carmen San Martín,1 Javier A. Velázquez-Muriel,1 Benes L. Trus,4 José L. Carrascosa,1 and José R. Castón1*

Departments of Structure of Macromolecules,1 Molecular and Cellular Biology, Centro Nacional de Biotecnología/CSIC, Cantoblanco, 28049 Madrid, Spain,2 Institut de Biologia Molecular de Barcelona/CSIC, Parc Científic de Barcelona, Josep Samitier 1-5, 08028 Barcelona, Spain,3 Imaging Sciences Laboratory, CIT, NIH, Bethesda, Maryland 20892-56244

Received 11 January 2007/ Accepted 6 April 2007

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.

* Corresponding author. Mailing address: Departamento de Estructura de Macromoléculas, Centro Nacional de Biotecnología/CSIC, C/ Darwin no. 3, Cantoblanco, E-28049 Madrid, Spain. Phone: 34-91-5854971. Fax: 34-91-5854506. E-mail: jrcaston{at}cnb.uam.es

{triangledown} Published ahead of print on 18 April 2007.

{dagger} Present address: Cancer Research UK, Clare Hall Laboratories, South Mimms, Herts EN6 3LD, United Kingdom.

Journal of Virology, July 2007, p. 6869-6878, Vol. 81, No. 13
0022-538X/07/$08.00+0     doi:10.1128/JVI.00077-07
Copyright © 2007, American Society for Microbiology. All Rights Reserved.



This article has been cited by other articles:

  • Delgui, L., Gonzalez, D., Rodriguez, J. F. (2009). Infectious bursal disease virus persistently infects bursal B-lymphoid DT40 cells. J. Gen. Virol. 90: 1148-1152 [Abstract] [Full Text]  
  • Irigoyen, N., Garriga, D., Navarro, A., Verdaguer, N., Rodriguez, J. F., Caston, J. R. (2009). Autoproteolytic Activity Derived from the Infectious Bursal Disease Virus Capsid Protein. J. Biol. Chem. 284: 8064-8072 [Abstract] [Full Text]  


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