THE ATOMIC STRUCTURE OF THE BLUETONGUE VIRUS CORE FROM X-RAY CRYSTALLOGRAPHY

J. M. Diprose¹, P. Gouet², J. N. Burroughs³, J. M. Grimes⁴, R. Malby¹, A. M. Wade-Evans³, S. Zeintara⁴, P. P. C. Mertens³ & D. I. Stuart¹

¹Laboratory of Molecular Biophysics, Oxford, UK,
²CNRS-IPBS, Toulouse, France,
³Institute for Animal Health, Pirbright, UK,
⁴EMBL Grenoble Outstation, Grenoble, France,
⁵Laboratoire Central de Recherches Veterinaires, Maison Alfort, France

Keywords: Virus Structure, X-Ray Crystallography, Macromolecular Assemblies, dsRNA Viruses, Orbiviruses, Bluetongue Virus.

We have determined the structures of the core particles of two bluetongue viruses (BTVs). The virus core is central to much of the virus life-cycle. It is infectious and acts as a transcriptional factory in the infected cell, sucking in nutrients and extruding capped mRNA segments which are used to produce the viral proteins and are encapsidated to form the next virus generation. The surface layer (radii 260-355Å) of the core contains 780 copies of T13 (formerly VP7), arr

We solved the structure of the core BTV-1 SA using X-ray techniques, with the aid of a 22Å cryo-EM reconstruction which we interpreted in terms of the known structure of T13[Ref1]. Extension of the resolution to 3.5Å allowed the atomic structure of all molecules of T13 and T2 to be determined. This allows us to propose a model for the assembly pathway, which explains the mixture of symmetry and asymmetry in the structure and may provide a paradigm for the assembly

The crystal structure of the core of BTV-10 USA has also been determined to 6Å. Through cross-averaging of these two structures we are able to make sense of a large amount of additional electron density that is found within the core. Four concentric layers of density are observed indicating that a large amount of the RNA genome is ordered into what is probably a liquid crystal, organised by the T2 layer. We now have a rough structural model for most of the important featu

1. Grimes, J. M., et al. An atomic model of the outer layer of the bluetongue virus core derived from X-ray crystallography and electron cryomicroscopy. Structure 5, 885-893 (1997).