Double-stranded (ds) RNA viruses infect a very wide range of host species, from bacteria to plants and animals. The Reoviridae, one of the most complex families in the dsRNA virus group, consists of at least 15 distinct genera reported to date. Two sub-families, Spinareovirinae and Sedoreovirinae, are currently classified by the International Committee for the Taxonomy of Viruses (ICTV) based on their particle structural organization (Makkay A, et al., 2011). The current structural information of reovirus particles and individual proteins from different genera has revealed an architectural principle common to some seemingly unrelated dsRNA viruses. In addition, it is also recognized that the structural organization of a number of dsRNA viruses placed in different genera also have similar biological functions in virus infection, even though they have widely divergent genome sequences. It is clear that meaningful sequence comparison is possible only between closely related viruses, an d the present methods of bioinformatics analysis are unable to recognize the similarities between different genera based on their sequence alignments only. Studies involving single-particle cryo-electron microscopy (cryo-EM) and three-dimensional (3D) image reconstruction of reovirus particles have shown that virus particle organization and structures of different virus types correspond to their function in viral infection and replication cycles. Analyses of reconstructed particle images obtained by these techniques have revealed a common evolutionary architectural principle for structurally different reoviruses, such as mammalian orthoreovirus (MRV, a turreted reovirus) or rotavirus (a non-turreted reovirus). In addition, the progress of cryo-EM techniques has fostered the use of structural information to understand the functions of these complex molecular structures. Recent studies have focused on high-resolution 3D structures of reovirus particles produced by cryo-EM, which approach the resolutions seen in structures identified by X-ray crystallography (Zhang X et al., 2008, 2010a; Settembre E C, et al., 2011; Yu X, et al., 2008). Some results determined by near-atomic resolution reconstructions using cryo-EM allow integration of structural a nd functional information into a coherent mechanism for understanding reovirus assembly and entry. Of the resolved 3D structures, the orthoreovirus, aquareovirus, and rotavirus structures have been well studied by cryo-EM. In this review, we summarize current progress on the structural basis of non-enveloped reovirus assembly and entry, mainly focusing on the MRV, aquareovirus, and rotavirus members of the Reoviridae family.
High-resolution 3D Structures Reveal the Biological Functions of Reoviruses
- Received Date: 05 May 2013
- Accepted Date: 30 September 2013
- Published Date: 06 November 2013
Abstract: Viruses in the family Reoviridae are non-enveloped particles comprising a segmented double-stranded RNA genome surrounded by a two-layered or multi-layered icosahedral protein capsid. These viruses are classified into two sub-families based on their particle structural organization. Recent studies have focused on high-resolution three-dimensional structures of reovirus particles by using cryo-electron microscopy (cryo-EM) to approach the resolutions seen in X-ray crystallographic structures. The results of cryo-EM image reconstructions allow tracing of most of the protein side chains, and thus permit integration of structural and functional information into a coherent mechanism for reovirus assembly and entry.