Structure of birnavirus-like particles determined by combined electron cryomicroscopy and X-ray crystallography.
Birnaviruses possess a capsid with a single protein layer in contrast to most double-stranded RNA viruses infecting multicellular eukaryotes. Using freeze-drying and heavy metal shadowing, the capsids of two birnaviruses, infectious bursal disease virus (IBDV) and infectious pancreatic necrosis virus, as well as of an IBDV virus-like particle (VLP) are shown to follow the same T=13 laevo icosahedral geometry. The structure of the VLP was determined at a resolution of approximately 15 A (1.5 nm) by a combination of electron cryomicroscopy and a recently developed three-dimensional reconstruction method, where the scattering density is expressed in terms of symmetry-adapted functions. This reconstruction methodology is well adapted to the icosahedral symmetry of viruses and only requires a small number of images to analyse. The atomic model of the external capsid protein, VP2, recently determined by X-ray crystallography, fits well into the VLP reconstruction and occupies all the electron densities present in the map. Thus, similarly to the IBDV virion, only VP2 forms the icosahedral layer of the VLP. The other components of both VLP and IBDV particles that play a crucial role in the capsid assembly, VP1, VP3 and the peptides arising from the processing of pVP2, do not follow the icosahedral symmetry, allowing them to be involved in other processes such as RNA packaging.
Pous
Joan
J
Laboratoire de Virologie Moléculaire et Structurale, UMR 2472 CNRS-INRA, 1 avenue de la terrasse, F-91198 Gif-sur-Yvette, France.
Chevalier
Christophe
C
Unité de Virologie et Immunologie Moléculaires, Domaine de Vilvert, INRA, F-78350 Jouy-en-Josas, France.
Ouldali
Malika
M
Laboratoire de Virologie Moléculaire et Structurale, UMR 2472 CNRS-INRA, 1 avenue de la terrasse, F-91198 Gif-sur-Yvette, France.
Navaza
Jorge
J
Laboratoire de Virologie Moléculaire et Structurale, UMR 2472 CNRS-INRA, 1 avenue de la terrasse, F-91198 Gif-sur-Yvette, France.
Delmas
Bernard
B
Unité de Virologie et Immunologie Moléculaires, Domaine de Vilvert, INRA, F-78350 Jouy-en-Josas, France.
Lepault
Jean
J
Laboratoire de Virologie Moléculaire et Structurale, UMR 2472 CNRS-INRA, 1 avenue de la terrasse, F-91198 Gif-sur-Yvette, France.
D018059:Birnaviridae / Q000737:chemistry / Q000648:ultrastructure*; D036022:Capsid Proteins / Q000648:ultrastructure; D020285:Cryoelectron Microscopy; D018360:Crystallography, X-Ray; D007243:Infectious bursal disease virus / Q000737:chemistry / Q000648:ultrastructure; D018061:Infectious pancreatic necrosis virus / Q000737:chemistry / Q000648:ultrastructure; D008958:Models, Molecular
D036022:Capsid Proteins