The Structure and Function of the Outer Coat Protein VP9 of Banna Virus

Cryo-EM structures of Banna virus in multiple states reveal stepwise detachment of viral spikes

Banna virus (BAV) is the prototype Seadornavirus, a class of reoviruses for which there has been little structural study. Here, we report atomic cryo-EM structures of three states of BAV virions-surrounded by 120 spikes (full virions), 60 spikes (partial virions), or no spikes (cores). BAV cores are double-layered particles similar to the cores of other non-turreted reoviruses, except for an additional protein component in the outer capsid shell, VP10. VP10 was identified to be a cementing protein that plays a pivotal role in the assembly of BAV virions by directly interacting with VP2 (inner capsid), VP8 (outer capsid), and VP4 (spike). Viral spikes (VP4/VP9 heterohexamers) are situated on top of VP10 molecules in full or partial virions. Asymmetrical electrostatic interactions between VP10 monomers and VP4 trimers are disrupted by high pH treatment, which is thus a simple way to produce BAV cores. Low pH treatment of BAV virions removes only the flexible receptor binding protein VP9 and triggers significant conformational changes in the membrane penetration protein VP4. BAV virions adopt distinct spatial organization of their surface proteins compared with other well-studied reoviruses, suggesting that BAV may have a unique mechanism of penetration of cellular endomembranes.

Detection, Characterization and Sequencing of BTV Serotypes Circulating in Cuba in 2022

In Cuba, despite a high sero-prevalence of bluetongue virus (BTV), circulating serotypes remain unknown. The aim of this study was to identify circulating BTV serotypes in farms throughout the western region of Cuba. Blood samples were collected from 200 young cattle and sheep between May and July 2022 for virological analyses (PCR, viral isolation and virus neutralization) and genome sequencing. The results confirmed viral circulation, with viro-prevalence of 25% for BTV. The virus was isolated from 18 blood samples and twelve BTV serotypes were identified by sequencing RT-PCR products targeting the segment 2 of the BTV genome (BTV-1, 2, 3, 6, 10, 12, 13, 17, 18, 19, 22 and 24). Finally, the full genome sequences of 17 Cuban BTV isolates were recovered using a Sequence Independent Single Primer Amplification (SISPA) approach combined to MinION Oxford Nanopore sequencing technology. All together, these results highlight the co-circulation of a wide diversity of BTV serotypes in a quite restricted area and emphasize the need for entomological and livestock surveillance, particularly in light of recent changes in the global distribution and nature of BTV infections.

Full genome characterization and evolutionary analysis of Banna virus isolated from Culicoides, mosquitoes and ticks in Yunnan, China

Introduction

Banna virus (BAV), a potential pathogen that may cause human encephalitis, is the prototype species of genus Seadornaviru within the family Reoviridae, and has been isolated from a variety of blood-sucking insects and mammals in Asia.

Methods

Culicoides, Mosquitoes, and Ticks were collected overnight in Yunnan, China, during 2016-2023 using light traps. Virus was isolated from these collected blood-sucking insects and grown using Aedes albopictus (C6/36) cells. Preliminary identification of the virus was performed by agarose gel electrophoresis (AGE). The full genome sequences of the BAVs were determined by full-length amplification of cDNAs (FLAC) and sequenced using next-generation sequencing.

Results

In this study, 13 strains BAV were isolated from Culicoides, Mosquitoes and Ticks. Their viral genome consisted of 12 segments of double-stranded RNA (dsRNA), and with three distinct distribution patterns. Sequence analysis showed that Seg-5 of four strains (SJ_M46, SJ_M49, JC_M19-13 and JC_C24-13) has 435 bases nucleotide sequence insertions in their ORF compared to other BAVs, resulting in the length of Seg-5 up to 2128 nt. There are 34 bases sequence deletion in Seg-9 of 3 strains (WS_T06, MS_M166 and MS_M140). Comparison of the coding sequences of VP1, VP2, VP5, VP9 and VP12 of the 13 BAV strains, the results show that VP1, VP2 and VP12 are characterised by high levels of sequence conservation, while VP9 is highly variable, under great pressure to adapt and may be correlated with serotype. While also variable, VP5 appears to be under less adaptive pressure than VP9. Additionally, phylogenetic analysis indicates that the 13 BAV strains locate in the same evolutionary cluster as BAVs isolated from various blood-sucking insects, and are clustered according to geographical distribution.

Conclusion

The data obtained herein would be beneficial for the surveillance of evolutionary characteristics of BAV in China and neighboring countries as well as extend the knowledge about its genomic diversity and geographic distribution.

Presence, Location and Conservation of Putative G-Quadruplex Forming Sequences in Arboviruses Infecting Humans

Guanine quadruplexes (G4s) are non-canonical nucleic acid structures formed by guanine (G)-rich tracts that assemble into a core of stacked planar tetrads. G4s are found in the human genome and in the genomes of human pathogens, where they are involved in the regulation of gene expression and genome replication. G4s have been proposed as novel pharmacological targets in humans and their exploitation for antiviral therapy is an emerging research topic. Here, we report on the presence, conservation and localization of putative G4-forming sequences (PQSs) in human arboviruses. The prediction of PQSs was performed on more than twelve thousand viral genomes, belonging to forty different arboviruses that infect humans, and revealed that the abundance of PQSs in arboviruses is not related to the genomic GC content, but depends on the type of nucleic acid that constitutes the viral genome. Positive-strand ssRNA arboviruses, especially Flaviviruses, are significantly enriched in highly conserved PQSs, located in coding sequences (CDSs) or untranslated regions (UTRs). In contrast, negative-strand ssRNA and dsRNA arboviruses contain few conserved PQSs. Our analyses also revealed the presence of bulged PQSs, accounting for 17-26% of the total predicted PQSs. The data presented highlight the presence of highly conserved PQS in human arboviruses and present non-canonical nucleic acid-structures as promising therapeutic targets in arbovirus infections.

Multi-epitope based subunit vaccine construction against Banna virus targeting on two outer proteins (VP4 and VP9): A computational approach

Recently, RNA viruses have gained a mammoth concern for causing various outbreaks, and due to pandemics, they are acquiring additional attention throughout the world. An emerging RNA as well as vector-borne Banna Virus (BAV) is a human pathogen resulting in encephalitis, fever, headache, muscle aches, and severe coma. Besides human, pathogenic BAV was also detected from pigs, cattle, ticks, midges, and mosquitoes in Indonesia, China, and Vietnam. Due to high mutation tendency and dearth of a species barrier, this virus will consider as a significant threat in the near future throughout the planet, particularly in Africa. Despite of severe human case fatalities in several countries, there are no specific therapeutics, available vaccines, and other preventive measures against BAV. Thus, to find out the effective therapeutics and preventive strategies are crying exigency. In the present study, a unique multi-epitope-based peptide vaccine candidate is constructed using bioinformatics' tools that efficiently instigate immune cells for generating BAV antibodies. The potential vaccine candidates were developed using both T and B -cell epitopes. UniprotKB database was used to retrieve of two outer proteins (VP9 and VP4), and homologous sequences of BAV taxid: 7763, 649,604, 77,763, and 8453 were searched by NCBI BLAST. These serotypes are the most closely associated with the disease. Then combining the best-selected epitopes in various combinations with different adjuvants, three distinct vaccine candidates were formed. The validity tests were performed for the screened vaccine candidate regarding stability, allergenicity, and antigenicity parameters. Moreover, molecular dynamic simulations of the selected vaccine with TLR-8 immune receptor confirmed the stability of the binding pose and showed a significant response to immune cells. Thus, the results established that the designed chimeric peptide vaccine could enhance the immune response against BAV.

A combinatorial approach of structure-based virtual screening and molecular dynamics simulation towards the discovery of a highly selective inhibitor for VP9 coat protein of Banna virus

Structure based virtual screening of two libraries containing 27,628 numbers of antiviral compounds was used to discover a few of the potent inhibitor molecules against Banna virus (BAV). Cross-docking studies with many common interfering proteins provided five of the highly selective inhibitor for BAV. Analyses of the leading molecules with ADME-Tox filtering tool and atomistic molecular dynamics simulation studies finally discovered a benzoxazolone derivative as one of the most promising molecules towards the highly selective inhibition of BAV. The theoretical calculations are also supported by the experimental evidences where the interactions between the hit ligand and a model peptide sequence, mimicking the VP9 protein of BAV, were studied. Overall the development of a personalized therapeutic towards the highly selective inhibition of BAV is discussed herein for the first time in literature.

First Isolation and Characterization of a Group C Banna Virus (BAV) from Anopheles sinensis Mosquitoes in Hubei, China

Banna virus (BAV) is considered to be an emerging human pathogen that is transmitted by blood-sucking insects. BAV was isolated from various species of mosquitoes, midges, and livestock. It is widely distributed geographically, since it was identified in China, Vietnam, and Indonesia. Previously reported evolution studies of BAV indicated that BAV can be divided into two groups, including isolates from China and Vietnam clustered in group A, and Indonesian isolates in group B. In this study, we report the isolation of a new strain of BAV named HB14-71-01 from Anopheles sinensis mosquitoes from Hubei, China. An in vitro comparison study of the HB14-71-01 isolate and the group A BAV revealed differences based on observed cytopathic effect, plaque size, and viral growth rates. Additionally, the phylogenetic analysis indicated that the Hubei isolate belongs to a novel genotype of BAV and emerged nearly 105 years ago (95% highest posterior density (HPD): 35–434), unlike the two previously reported genotypes A and B. Our findings extend the knowledge about the genomic diversity and potential vectors/hosts of BAVs and will improve understanding of the relationships between genetic variation and pathogenicity.

Analysis of compositional bias and codon usage pattern of the coding sequence in Banna virus genome

By using DNA Star, CUSP of EMBOSS, Codon W and IBM SPSS Statistics, nucleotide composition and codon usage pattern of 115 genes are researched in 37 BAVs. It shows that the composition of all genes prefers to AU, compared to CG, and for most of genes, the order is A, U, G and C in the virus. The ENC-values of the genes are slightly high which shows the weak codon bias, in which the codon bias of VP9 gene is the highest. The codon usage pattern of 12 different genes is different and related to their composition, their function or their host. For example, VP9 gene encoding viral spike protein in contact with different hosts spread dispersedly and VP1, VP2, VP3 and VP4 genes encoding the capsid protein are concentrated on first quadrant in correspondence analysis. The ENC of VP5 is correlated to GC_3s in correlation analysis. The points of VP12 gene are tightly close to the expected curve in the ENC-plot analysis but GC₁₂ is not related to GC₃ in neutrality analysis. All analysis indicates the codon usage pattern of 12 genes is influenced by both natural selection and neutral mutation in a different extent in BAV. As a pathogen of viral encephalitis, compositional analysis and codon bias analysis of BAV can provide a theoretical basis for the disease control.

An RNA Virome Associated to the Golden Orb-Weaver Spider Nephila clavipes

The golden orb-weaver spider Nephila clavipes, known for its sexual size dimorphism, is abundant and widespread in the New World. The first annotated genome of orb-weaver spiders, exploring N. clavipes, has recently been reported. The study, focused primarily on the diversity of silk specific genes, shed light into the complex evolutionary history of spiders. Furthermore, a robust transcriptome analysis provided a massive resource for N. clavipes RNA survey. Here, I present evidence of viral sequences corresponding to the first 10 extant virus species associated to N. clavipes and indeed, nephilids. The putatively new species are linked to ssRNA positive-strand viruses, such as Picornavirales, and to ssRNA negative-strand and dsRNA viruses. In addition, I detected sequence data of new strains of two recently reported arthropod viruses, which complemented and extended the corresponding sequence references. The identified viruses appear to be complete, potentially functional, and presenting the typical architecture and consistent viral domains. The intrinsic nature of the detected sequences and their absence in the recently generated genome assembly, suggest that they correspond to bona fide RNA virus sequences. The available RNA data allowed for the first time to address a tissue/organ specific analysis of virus loads/presence in spiders, suggesting a complex spatial and differential distribution of the tentative viruses, encompassing the spider brain and also silk and venom glands. Until recently, the virus landscape associated to spiders remained elusive. The discovered viruses described here provide only a fragmented glimpse of the potential magnitude of the Aranea virosphere. Future studies should focus not only on complementing and expanding these findings, but also on addressing the potential ecological role of these viruses, which might influence the biology of these outstanding arthropod species.

Double-stranded RNA virus outer shell assembly by bona fide domain-swapping

Correct outer protein shell assembly is a prerequisite for virion infectivity in many multi-shelled dsRNA viruses. In the prototypic dsRNA bacteriophage φ6, the assembly reaction is promoted by calcium ions but its biomechanics remain poorly understood. Here, we describe the near-atomic resolution structure of the φ6 double-shelled particle. The outer T=13 shell protein P8 consists of two alpha-helical domains joined by a linker, which allows the trimer to adopt either a closed or an open conformation. The trimers in an open conformation swap domains with each other. Our observations allow us to propose a mechanistic model for calcium concentration regulated outer shell assembly. Furthermore, the structure provides a prime exemplar of bona fide domain-swapping. This leads us to extend the theory of domain-swapping from the level of monomeric subunits and multimers to closed spherical shells, and to hypothesize a mechanism by which closed protein shells may arise in evolution.

Double-shelled bacteriophage φ6 is a well-studied model system used to understand assembly of dsRNA viruses. Here the authors report a near-atomic resolution cryo-EM structure of φ6 and propose a model for the structural transitions occurring in the outer shell during genome packaging.

Spot the difference-development of a syndrome based protein microarray for specific serological detection of multiple flavivirus infections in travelers

Background

The family Flaviviridae, genus Flavivirus, holds many of the world’s most prevalent arboviral diseases that are also considered the most important travel related arboviral infections. In most cases, flavivirus diagnosis in travelers is primarily based on serology as viremia is often low and typically has already been reduced to undetectable levels when symptoms set in and patients seek medical attention. Serological differentiation between flaviviruses and the false-positive results caused by vaccination and cross-reactivity among the different species, are problematic for surveillance and diagnostics of flaviviruses. Their partially overlapping geographic distribution and symptoms, combined with increase in travel, and preexisting antibodies due to flavivirus vaccinations, expand the need for rapid and reliable multiplex diagnostic tests to supplement currently used methods.

Goal

We describe the development of a multiplex serological protein microarray using recombinant NS1 proteins for detection of medically important viruses within the genus Flavivirus. Sera from clinical flavivirus patients were used for primary development of the protein microarray.

Results

Results show a high IgG and IgM sensitivity and specificity for individual NS1 antigens, and limited cross reactivity, even within serocomplexes. In addition, the serology based on this array allows for discrimination between infection and vaccination response for JEV vaccine, and no cross-reactivity with TBEV and YFV vaccine induced antibodies when testing for antibodies to other flaviviruses.

Conclusion

Based on these data, multiplex NS1-based protein microarray is a promising tool for surveillance and diagnosis of flaviviruses.

The number of international travelers has increased dramatically in recent decades. This has contributed to the increase in infectious diseases in travelers which are not present in their countries of origin and so may cause a threat to the public health. Viruses transmitted by biting insects (vector-borne viruses) are an important group within these travel-related diseases. They are found across the world and can cause debilitating and life-threatening symptoms, like inflammation of the brain or excessive bleeding. Many of these diseases are difficult to distinguish from each other. They cause comparable symptoms and are genetically closely related. Testing for long lists of diseases is time consuming and expensive. Here we develop a novel testing tool that allows doctors and researchers to test for multiple viruses with just one test. The method, which uses a specific part of the virus that makes distinguishing between infections with these closely related viruses possible, requires only one drop of blood. This allows us to test for multiple viruses simultaneously with the same amount of blood previously used to test for only one virus, while distinguishing between genetically closely related viruses.

Isolates of Liao ning virus from wild-caught mosquitoes in the Xinjiang province of China in 2005

Liao ning virus (LNV) is related to Banna virus, a known human-pathogen present in south-east Asia. Both viruses belong to the genus Seadornavirus, family Reoviridae. LNV causes lethal haemorrhage in experimentally infected mice. Twenty seven isolates of LNV were made from mosquitoes collected in different locations within the Xinjiang province of north-western China during 2005. These mosquitoes were caught in the accommodation of human patients with febrile manifestations, or in animal barns where sheep represent the main livestock species. The regions where LNV was isolated are affected by seasonal encephalitis, but are free of Japanese encephalitis (JE). Genome segment 10 (Seg-10) (encoding cell-attachment and serotype-determining protein VP10) and Seg-12 (encoding non-structural protein VP12) were sequenced for multiple LNV isolates. Phylogenetic analyses showed a less homogenous Seg-10 gene pool, as compared to segment 12. However, all of these isolates appear to belong to LNV type-1. These data suggest a relatively recent introduction of LNV into Xinjiang province, with substitution rates for LNV Seg-10 and Seg-12, respectively, of 2.29×10⁻⁴ and 1.57×10⁻⁴ substitutions/nt/year. These substitution rates are similar to those estimated for other dsRNA viruses. Our data indicate that the history of LNV is characterized by a lack of demographic fluctuations. However, a decline in the LNV population in the late 1980s - early 1990s, was indicated by data for both Seg-10 and Seg-12. Data also suggest a beginning of an expansion in the late 1990s as inferred from Seg-12 skyline plot.

Detection of a fourth orbivirus non-structural protein

The genus Orbivirus includes both insect and tick-borne viruses. The orbivirus genome, composed of 10 segments of dsRNA, encodes 7 structural proteins (VP1–VP7) and 3 non-structural proteins (NS1–NS3). An open reading frame (ORF) that spans almost the entire length of genome segment-9 (Seg-9) encodes VP6 (the viral helicase). However, bioinformatic analysis recently identified an overlapping ORF (ORFX) in Seg-9. We show that ORFX encodes a new non-structural protein, identified here as NS4. Western blotting and confocal fluorescence microscopy, using antibodies raised against recombinant NS4 from Bluetongue virus (BTV, which is insect-borne), or Great Island virus (GIV, which is tick-borne), demonstrate that these proteins are synthesised in BTV or GIV infected mammalian cells, respectively. BTV NS4 is also expressed in Culicoides insect cells. NS4 forms aggregates throughout the cytoplasm as well as in the nucleus, consistent with identification of nuclear localisation signals within the NS4 sequence. Bioinformatic analyses indicate that NS4 contains coiled-coils, is related to proteins that bind nucleic acids, or are associated with membranes and shows similarities to nucleolar protein UTP20 (a processome subunit). Recombinant NS4 of GIV protects dsRNA from degradation by endoribonucleases of the RNAse III family, indicating that it interacts with dsRNA. However, BTV NS4, which is only half the putative size of the GIV NS4, did not protect dsRNA from RNAse III cleavage. NS4 of both GIV and BTV protect DNA from degradation by DNAse. NS4 was found to associate with lipid droplets in cells infected with BTV or GIV or transfected with a plasmid expressing NS4.

Complete characterisation of the American grass carp reovirus genome (genus Aquareovirus: family Reoviridae) reveals an evolutionary link between aquareoviruses and coltiviruses

An aquareovirus was isolated from several fish species in the USA (including healthy golden shiners) that is not closely related to members of species Aquareovirus A, B and C. The virus, which is atypical (does not cause syncytia in cell cultures at neutral pH), was implicated in a winter die-off of grass carp fingerlings and has therefore been called 'American grass carp reovirus' (AGCRV). Complete nucleotide sequence analysis of the AGCRV genome and comparisons to the other aquareoviruses showed that it is closely related to golden ide reovirus (GIRV) (>92% amino acid [aa] identity in VP5(NTPase) and VP2(Pol)). However, comparisons with grass carp reovirus (Aquareovirus C) and chum salmon reovirus (Aquareovirus A) showed only 22% to 76% aa identity in different viral proteins. These findings have formed the basis for the recognition of AGCRV and GIRV as members of a new Aquareovirus species 'Aquareovirus G' by ICTV. Further sequence comparisons to other members of the family Reoviridae suggest that there has been an 'evolutionary jump,' involving a change in the number of genome segments, between the aquareoviruses (11 segments) and coltiviruses (12 segments). Segment 7 of AGRCV encodes two proteins, from two distinct ORFs, which are homologues of two Coltivirus proteins encoded by genome segments 9 and 12. A similar model has previously been reported for the rotaviruses and seadornaviruses.

Viral proteomics

Viruses have long been studied not only for their pathology and associated disease but also as model systems for molecular processes and as tools for identifying important cellular regulatory proteins and pathways. Recent advances in mass spectrometry methods coupled with the development of proteomic approaches have greatly facilitated the detection of virion components, protein interactions in infected cells, and virally induced changes in the cellular proteome, resulting in a more comprehensive understanding of viral infection. In addition, a rapidly increasing number of high-resolution structures for viral proteins have provided valuable information on the mechanism of action of these proteins as well as aided in the design and understanding of specific inhibitors that could be used in antiviral therapies. In this paper, we discuss proteomic studies conducted on all eukaryotic viruses and bacteriophages, covering virion composition, viral protein structures, virus-virus and virus-host protein interactions, and changes in the cellular proteome upon viral infection.

Structural studies on orbivirus proteins and particles

X-ray and electron microscopy analysis of Bluetongue virus (BTV), the type species of the Orbivirus genus within the family Reoviridae, have revealed various aspects of the organisation and structure of the proteins that form the viral capsid. Orbiviruses have a segmented dsRNA genome, which imposes constraints on their structure and life cycle. The atomic structure of the BTV core particle, the key viral component which transcribes the viral mRNA within the cell cytoplasm, revealed the architecture and assembly of the major core proteins VP7 and VP3. In addition, these studies formed the basis for a plausible model for the organisation of the dsRNA viral genome and the arrangement of the viral transcriptase complex (composed of the RNA-dependent RNA polymerase, the viral capping enzyme and RNA helicase) that resides within the core particle. Electron cryo-microscopy of the viral particle has shown how the two viral proteins VP2 and VP5 are arranged to form the outer capsid, with distinct packing arrangements between them and the core protein VP7. By comparison of the outer capsid proteins of orbiviruses with those of other nonturreted members of the family Reoviridae, we are able to propose a more detailed model of these structures and possible mechanisms for cell entry. Further structural results are also discussed including the atomic structure of an N-terminal domain of nonstructural protein NS2, a protein involved in virus genome assembly and morphogenesis.

Liao ning virus, a new Chinese seadornavirus that replicates in transformed and embryonic mammalian cells

Seadornaviruses are emerging arboviral pathogens from the south-east of Asia. The genus Seadornavirus contains two distinct species, Banna virus (BAV) isolated from humans with encephalitis and Kadipiro virus. BAV replicates within insect cells and mice but not in cultured mammalian cells. Here, the discovery of Liao ning virus (LNV), a new seadornavirus from the Aedes dorsalis mosquito, which was completely sequenced and was found to be related to BAV and Kadipiro virus, is reported. Two serotypes of LNV could be distinguished by a serum neutralization assay. According to amino acid identity with other seadornaviruses, and to criteria set by the ICTV for species delineation, LNV was identified as a member of a new species of virus. Its morphology was characterized by electron microscopy and found to be similar to that of BAV. LNV is the first reported seadornavirus that replicates in mammalian cells, leading to massive cytopathic effect in all transformed or embryonic cell lines tested. LNV- and BAV-infected mice producing a viraemia lasting for 5 days was followed by viral clearance. Mice infection generated virus quasi-species for LNV (the first reported observation for quasi-species in the family Reoviridae) but not for BAV. Challenge with BAV in mice immunized against BAV did not lead to productive infection. However, challenge with LNV in mice immunized against LNV was lethal with a new phase of viraemia and massive haemorrhage.

Coltiviruses and seadornaviruses in North America, Europe, and Asia

Coltiviruses are tickborne viruses of the genus Coltivirus. The type species, Colorado tick fever virus (from North America), has been isolated from patients with flulike syndromes, meningitis, encephalitis, and other severe complications. Another coltivirus, Eyach virus, has been isolated from ticks in France and Germany and incriminated in febrile illnesses and neurologic syndromes. Seadornaviruses are endemic in Southeast Asia, particularly Indonesia and China. The prototype virus of the genus, Banna virus (BAV), has been isolated from many mosquito species, humans with encephalitis, pigs, and cattle. Two other seadornaviruses, Kadipiro and Liao Ning, were isolated only from mosquitoes. The epidemiology of seadornaviruses remains poorly documented. Evidence suggests that BAV is responsible for encephalitis in humans. Infection with BAV may be underreported because it circulates in regions with a high incidence of Japanese encephalitis and could be misdiagnosed as this disease.

Coupling of Rotavirus Genome Replication and Capsid Assembly

The Reoviridae family represents a diverse collection of viruses with segmented double-stranded (ds)RNA genomes, including some that are significant causes of disease in humans, livestock, and plants. The genome segments of these viruses are never detected free in the infected cell but are transcribed and replicated within viral cores by RNA-dependent RNA polymerase (RdRP). Insight into the replication mechanism has been provided from studies on Rotavirus, a member of the Reoviridae whose RdRP can specifically recognize viral plus (+) strand RNAs and catalyze their replication to dsRNAs in vitro. These analyses have revealed that although the rotavirus RdRP can interact with recognition signals in (+) strand RNAs in the absence of other proteins, the conversion of this complex to one that can support initiation of dsRNA synthesis requires the presence and partial assembly of the core capsid protein. By this mechanism, the viral polymerase can carry out dsRNA synthesis only when capsid protein is available to package its newly made product. By preventing the accumulation of naked dsRNA within the cell, the virus avoids triggering dsRNA-dependent interferon signaling pathways that can induce expression and activation of antiviral host proteins.

What does structure tell us about virus evolution?

Viruses are the most abundant life form and infect practically all organisms. Consequently, these obligate parasites are a major cause of human suffering and economic loss. The organization and origins of this enormous virosphere are profound open questions in biology. It has generally been considered that viruses infecting evolutionally widely separated organisms (e.g. bacteria and humans) are also distinct. However, recent research contradicts this picture. Structural analyses of virion architecture and coat protein topology have revealed unexpected similarities, not visible in sequence comparisons, suggesting a common origin for viruses that infect hosts residing in different domains of life (bacteria, archaea and eukarya).

Expansion of family Reoviridae to include nine-segmented dsRNA viruses: isolation and characterization of a new virus designated Aedes pseudoscutellaris reovirus assigned to a proposed genus (Dinovernavirus)

Family Reoviridae is known, by definition, to contain dsRNA viruses with 10-12 genome segments. We report here the characterization of the first member of this family with a nine-segmented genome. This virus was isolated from Aedes pseudoscutellaris mosquito cells and designated aedes pseudoscutellaris reovirus (APRV). Virions are single-shelled with turrets but are non-occluded by contrast to cypoviruses. APRV replicates in various mosquito cell lines, but not in mice or mammalian cells. Complete sequence analysis showed that APRV is phylogenetically related to cypoviruses, fijiviruses and oryzaviruses. The maximum amino acid identities with cypoviruses, oryzaviruses or fijiviruses in the polymerase, are compatible with values observed between these genera and lower than values within a given genus. This suggests that APRV should be classified within a new genus that we designated Dinovernavirus (sigla from D: Double-stranded, i: insect, nove: nine from the latin "novem", rna: RNA, virus) in family Reoviridae.

Structural organization of an encephalitic human isolate of Banna virus (genus Seadornavirus, family Reoviridae)

Banna virus (BAV) is the type species of the genus Seadornavirus within the family Reoviridae. The Chinese BAV isolate (BAV-Ch), which causes encephalitis in humans, was shown to have a structural organization and particle morphology reminiscent of that of rotaviruses, with fibre proteins projecting from the surface of the particle. Intact BAV-Ch virus particles contain seven structural proteins, two of which (VP4 and VP9) form the outer coat. The inner (core) particles contain five additional proteins (VP1, VP2, VP3, VP8 and VP10) and are ‘non-turreted’, with a relatively smooth surface appearance. VP2 is the ‘T=2’ protein that forms the innermost ‘subcore’ layer, whilst VP8 is the ‘T=13’ protein forming the core-surface layer. Sequence comparisons indicate that BAV VP9 and VP10 are equivalent to the VP8* and VP5* domains, respectively, of rotavirus outer-coat protein VP4 (GenBank accession no. P12976). VP9 has also been shown to be responsible for virus attachment to the host-cell surface and may be involved in internalization. These similarities reveal a previously unreported genetic link between the genera Rotavirus and Seadornavirus, although the expression of BAV VP9 and VP10 from two separate genome segments, rather than by the proteolytic cleavage of a single gene product (as seen in rotavirus VP4), suggests a significant evolutionary jump between the members of these two genera.