10/25/2022 0 Comments Obs download 21.1.1![]() Type 1 reovirus strains spread by hematogenous routes to the CNS where they infect ependymal cells, leading to non-lethal hydrocephalus ( Weiner et al., 1977, 1980 Tyler et al., 1986). After infection of newborn mice, reoviruses disseminate to the CNS and produce serotype-specific patterns of disease ( Tyler and Fields, 1996). They also serve as important models for studies of viral replication and pathogenesis and, in particular, for analysis of viral determinants of central nervous system (CNS) injury. Reoviruses infect most children and can cause mild respiratory or gastrointestinal illnesses ( Tyler and Fields, 1996). Three major reovirus serotypes have been described, which are represented by the prototype strains type 1 Lang (T1L), type 2 Jones (T2J) and type 3 Dearing (T3D). Reoviruses have been isolated from many mammalian species, including humans ( Tyler and Fields, 1996). The σ1 tail partially inserts into the virion via ‘turrets’ formed by the pentameric λ2 protein, whereas the σ1 head projects away from the virion surface ( Furlong et al., 1988 Dryden et al., 1993). Rotary shadowing studies show that σ1 is a long, fiber-like molecule with head-and-tail morphology and several defined regions of flexibility within its tail ( Fraser et al., 1990). The reovirus σ1 protein serves as the viral attachment protein ( Weiner et al., 1980 Lee et al., 1981). The σ3 protein, whose crystal structure is known ( Olland et al., 2001), is thought to serve as a protective cap for μ1, and cleavage of σ3 by endosomal proteases during viral infection results in the loss of σ3 and generation of infectious subvirion particles. ![]() A second layer of proteins (μ1, σ1 and σ3) forms the reovirus outer capsid, with μ1 and σ3 comprising the bulk of this capsid and σ1 protruding from the 12 vertices of the icosahedron. Five of these (λ1, λ2, λ3, μ2 and σ2) form the ‘core’ or inner capsid particle, the crystal structure of which has been determined ( Reinisch et al., 2000). The virions measure ∼850 Å in diameter and are composed of eight structural proteins. Reoviruses form non-enveloped, icosahedral particles ( Dryden et al., 1993) that contain a segmented double-stranded (ds) RNA genome. The architecture of the trimer interface and the observed flexibility indicate that σ1 is a metastable structure poised to undergo conformational changes upon viral attachment and cell entry. The fibrous tail is mainly responsible for σ1 trimer formation, and it contains a highly flexible region that allows for significant movement between the base of the tail and the head. A prominent loop in the σ1 head contains a cluster of residues that are conserved among reovirus serotypes and are likely to form a binding site for junction adhesion molecule, an integral tight junction protein that serves as a reovirus receptor. ![]() ![]() Numerous structural and functional similarities between reovirus σ1 and the adenovirus fiber suggest an evolutionary link in the receptor-binding strategies of these two viruses. The crystal structure of a receptor-binding fragment of σ1 reveals an elongated trimer with two domains: a compact head with a new β-barrel fold and a fibrous tail containing a triple β-spiral. Reovirus attaches to cellular receptors with the σ1 protein, a fiber-like molecule protruding from the 12 vertices of the icosahedral virion. ![]()
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