Reovirus structure

The mammalian reoviruses are divided into three serotypes (1, 2, and 3) on the basis of hemagglutination inhibition and antibody neutralization tests (Rosen, 1960). Reovirions contain a segmented, double-stranded RNA (dsRNA) genome surrounded by two concentric icosahedral protein shells (Gomatos et ai, 1962). There is an internal core containing the genome and a closely applied inner capsid surrounded by an outer capsid shell (Smith et ai, 1969 Fig. 1). 

Assembly of reovirus particles in vitro has proved useful for studies of structure-function relationships of viral outer capsid proteins. Particles obtained by mixing baculovirus-expressed cr3 with ISVPs are similar to 

Although many reovirus strains efficiently replicate in the intestine, not all strains do. In fact, T3D fails to grow in the intestine and does not spread to the CNS following oral inoculation. However, infection by either 

These studies indicate that susceptibility of the reovirus attachment protein to host proteases influences growth in the murine intestine and systemic spread. Although protease-treated T3D virions lack the capacity to infect intestinal cells, they retain the capacity to infect other cell types in culture and in vivo. These findings suggest that T3D al contains two 

The (j1 Tail Binds Cell Surface Sialic Acid 

Reovirus-Receptor Interactions Promote Cell Death 

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Fig. 1. Schematic drawings of the viruses discussed in this chapter. (A) An icosahe-dral virus with fiber proteins inserted in its pentameric vertices. The gray box denotes domains with known structures for adenovirus, reovirus, and bacteriophage PRD1, in each case containing the head domain and proximal part of the triple /8-spiral shaft domain. (B) Contractile-tailed bacteriophage T4. T4 contains three different fibrous proteins, fibritin connected to the neck, the long (bent) fibers connected to the base plate, and the short fibers also connected to the base plate. Only two of each of the trimeric fibrous proteins are shown for clarity. The gray box denotes domains with known structure for the T4 short fiber.

More recently, triple /1-spiral repeats have been identified in mammalian reovirus type 3 fiber (Chappell et al., 2002 Fig. 4A), avian reovirus fiber (Guardado Calvo et al., 2005 Fig. 4B), and bacteriophage PRD1 P5 protein (Merckel et al., 2005 Fig. 4C). In the latter two cases, it appears that only two repeats are present, just N-terminal to the head domain. Mammalian reovirus fiber contains eight putative triple /1-spiral repeats, of which three were resolved in the crystal structure (Chappell et al., 2002). 

Chappell, J. D., Prota, A. E., Dermody, T. S., and Stehle, T. (2002). Crystal structure of reovirus attachment protein sigmal reveals evolutionary relationship to adenovirus fiber. EMBOJ. 21, 1-11. 

Guardado Calvo, P., Fox, G. C., Hermo Parrado, X. L., Llamas-Saiz, A. L., Costas, C., Martinez-Costas, J., Benavente, J., and van Raaij, M. J. (2005). Structure of the carboxy-terminal receptor-binding domain of avian reovirus fibre sigmaC. / Mol. Biol. 354, 137-149. 

Where the structure of one or more similar viruses is available, low-resolution starting phases can be calculated from the model virus (or summed structures) correctly placed in the cell of the unknown structure (Fry et al., 1993). Cryo-EM reconstructions can provide adequate starting phases and envelope information for the determination of novel structures, for example BTV (Grimes effl/., 1998), Reovirus... 

At the far left, we can see the nucleic acid and protein structures shown in frame 1. In addition, we show a much larger protein, the immunoglobulin G antibody molecule. Four separate polypeptide chains join to make up an antibody molecule two heavy chains (blue) of about 400 amino acids and two light chains (purple) of about 200 amino acids. The antibody is about 16 nm in width. Finally, at the far right, we show the core particle from a small plant virus, the reovirus. Only the icosahedral protein coat of the virus can be seen. The reovirus particle is about 60 nm across. The nucleic acids of the virus are sequestered inside the virus core. The reovirus family is unusual in that its nucleic acids are all double-stranded RNA molecules. 

Expression of viral structural proteins in a heterologous system does not always lead to formation of the desired assembly intermediate or end product. This is particularly the case when the proteins are expressed in E. coli or when individual components are expressed separately in different cells. In these cases, the proteins are usually purified and then assembled in vitro. Alternatively, assembly is possible using whole cell lysates. For example, assembly of HSV-1 capsids, which requires a minimum of four structural proteins, was observed on mixing of lysates derived from insect cells infected with different baculovirus vectors (Newcomb et al, 1994). Similarly, reovirus cores, obtained from native virions, could be... 

Fig. 5. Structural classification of Reoviridae architecture, (a) Bluetongue virus, a typical orbivirus (Grimes et al, 1998). (b) Orthoreovirus, a typical reovirus (Reinisch et al, 2000). (c) CPV, a typical cypovirus (Hill et ai, 1999).

The fxS protein is associated with the fil protein, and a complex of these proteins has been determined (Liemann et al., 2002). /il forms a T=13 layer in the reovirus particles but is not present in the crystal structure of the capsid (Reinisch et al., 2000). The protein is similar to OrbivirusYPl in that it has a jelly-roll domain positioned external to a base formed mostly by helices. The jelly-roll domain contains a few extra strands, and in the sequence it is flanked by the residues forming the helical region. Although this is true also for the corresponding region in VP7 of bluetongue virus, the fold in this part of the protein is different. 

Dryden, K. A., Wang, G., Yeager, M., Nibert, M. L., Coombs, K. M., Furlong, D. B., Fields, B. N., and Baker, T. S. (1993). Early steps in reovirus infection are associated with dramatic changes in supramolecular structure and protein conformation Analysis of virions and subviral particles by cryoelectron microscopy and image reconstruction./. Cell Biol. 122, 1023-1041. 

Virgin, H. W. I., Mann, M. A., Fields, B. N., and Tyler, K. L. (1991). Monoclonal antibodies to reovirus reveal structure/function relationships between capsid proteins and genetics of susceptibility to antibody action./ Virol. 65, 6772-6781. 

Olland, A. M., Jane-Valbuena, J., Schiff, L. A., Nibert, M. L., and Harrison, S. C. (2001). Structure of the reovirus outer capsid and dsRNA-binding protein cr3 at... 

Chapman and Liljas, Fig. 12. The shell-forming proteins of bluetongue virus and reovirus (a) bluetongue VPS protein (Grimes et al, 1998) (b) reovirus 11 protein (Reinisch et al., 2000). In the bluetongue VPS protein, three domains (apical, carapace, and dimerization domains) have been identified. The secondary structure elements have been colored to emphasize the general structural similarity between the two proteins. 

Stewart etal.. Fig. 3. The crystallographic structure of the reovirus core composed of 120 copies of 11 (red), 150 copies of cr2 (yellow, green, and white), and 60 copies of 12 (blue). The traces are displayed and the view is along a 5-fold symmetry axis. [Reproduced with copyright permission from Nature (Reinisch et al., 2000).]... 

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