Structure of avian orthoreovirus virion by electron cryomicroscopy and image reconstruction

Abstract

Among members of the genus Orthoreovirus, family Reoviridae, a group of non-enveloped viruses with genomes comprising ten segments of double-stranded RNA, only the "non-fusogenic" mammalian orthoreoviruses (MRVs) have been studied to date by electron cryomicroscopy and three-dimensional image reconstruction. In addition to MRVs, this genus comprises other species that induce syncytium formation in cultured cells, a property shared with members of the related genus Aquareovirus. To augment studies of these "fusogenic" orthoreoviruses, we used electron cryomicroscopy and image reconstruction to analyze the virions of a fusogenic avian orthoreovirus (ARV). The structure of the ARV virion, determined from data at an effective resolution of 14.6 A, showed strong similarities to that of MRVs. Of particular note, the ARV virion has its pentameric lambda-class core turret protein in a closed conformation as in MRVs, not in a more open conformation as reported for aquareovirus. Similarly, the ARV virion contains 150 copies of its monomeric sigma-class core-nodule protein as in MRVs, not 120 copies as reported for aquareovirus. On the other hand, unlike that of MRVs, the ARV virion lacks "hub-and-spokes" complexes within the solvent channels at sites of local sixfold symmetry in the incomplete T=13l outer capsid. In MRVs, these complexes are formed by C-terminal sequences in the trimeric mu-class outer-capsid protein, sequences that are genetically missing from the homologous protein of ARVs. The channel structures and C-terminal sequences of the homologous outer-capsid protein are also genetically missing from aquareoviruses. Overall, the results place ARVs between MRVs and aquareoviruses with respect to the highlighted features.

Reovirus Outer Capsid Protein μ1 Induces Apoptosis and Associates with Lipid Droplets, Endoplasmic Reticulum, and Mitochondria

“…We have found that expression of the ARV-176 B protein (the homolog of 1) also robustly induces apoptosis in transfected cells (C. M. Coffey and J. S. L. Parker, unpublished data). We note that ARV B lacks the C-terminal extension (68), including the putative PEST motif found in 1, and we are currently investigating the role of this region of 1 in protein stability.…”

“…To identify the region(s) of 1 responsible for its activities in the preceding Results sections, we constructed a series of M2 gene truncations that encode the near-equivalents of each of these fragments (as some constructs have the addition of an initiating methionine residue at the N terminus). In addition, we prepared a construct to encode full-length 1 lacking only residues 676 to 708 [1(1-675)], which are disordered in the 1:3 crystal structure and genetically absent from the 1 homologs of avian reoviruses and aquareoviruses (1,37,43,68). Because none of the available anti-1 MAbs (62) recognize the 1N or fragment, we prepared constructs to express EGFP-tagged versions of those regions.…”

Ab initio random model method facilitates 3D reconstruction of icosahedral particles

“…the dextro enantiomers). To be consistent with all other orthoreoviruses studied to date (Zhang, et al, 2005b), we reversed the hands of the two BRV maps to make each a T=13l structure (the laevo enantiomer) consistent with that shown in Fig. 6.…”

β1 Integrin Mediates Internalization of Mammalian Reovirus

“…The trimeric attachment proteins of both viruses, 1 and fiber, respectively, are structural homologues and fold using a highly unusual triple ␤-spiral motif (10,20,83). The globular head domains of these molecules are formed from eight-stranded ␤-barrels with identical interstrand connectivity (70).…”