Assembly and intracellular localization of the bluetongue virus core protein VP3

Assessing Reassortment between Bluetongue Virus Serotypes 10 and 17 at Different Coinfection Ratios in Culicoides sonorenesis

Bluetongue virus (BTV) is a segmented, double-stranded RNA orbivirus listed by the World Organization for Animal Health and transmitted by Culicoides biting midges. Segmented viruses can reassort, which facilitates rapid and important genotypic changes. Our study evaluated reassortment in Culicoides sonorensis midges coinfected with different ratios of BTV-10 and BTV-17. Midges were fed blood containing BTV-10, BTV-17, or a combination of both serotypes at 90:10, 75:25, 50:50, 25:75, or 10:90 ratios. Midges were collected every other day and tested for infection using pan BTV and cox1 (housekeeping gene) qRT-PCR. A curve was fit to the ∆Ct values (pan BTV Ct-cox1 Ct) for each experimental group. On day 10, the midges were processed for BTV plaque isolation. Genotypes of the plaques were determined by next-generation sequencing. Pairwise comparison of ∆Ct curves demonstrated no differences in viral RNA levels between coinfected treatment groups. Plaque genotyping indicated that most plaques fully aligned with one of the parental strains; however, reassortants were detected, and in the 75:25 pool, most plaques were reassortant. Reassortant prevalence may be maximized upon the occurrence of reassortant genotypes that can outcompete the parental genotypes. BTV reassortment and resulting biological consequences are important elements to understanding orbivirus emergence and evolution.

A multidisciplinary approach to the identification of the protein-RNA connectome in double-stranded RNA virus capsids

How multi-segmented double-stranded RNA (dsRNA) viruses correctly incorporate their genomes into their capsids remains unclear for many viruses, including Bluetongue virus (BTV), a Reoviridae member, with a genome of 10 segments. To address this, we used an RNA-cross-linking and peptide-fingerprinting assay (RCAP) to identify RNA binding sites of the inner capsid protein VP3, the viral polymerase VP1 and the capping enzyme VP4. Using a combination of mutagenesis, reverse genetics, recombinant proteins and in vitro assembly, we validated the importance of these regions in virus infectivity. Further, to identify which RNA segments and sequences interact with these proteins, we used viral photo-activatable ribonucleoside crosslinking (vPAR-CL) which revealed that the larger RNA segments (S1-S4) and the smallest segment (S10) have more interactions with viral proteins than the other smaller segments. Additionally, using a sequence enrichment analysis we identified an RNA motif of nine bases that is shared by the larger segments. The importance of this motif for virus replication was confirmed by mutagenesis followed by virus recovery. We further demonstrated that these approaches could be applied to a related Reoviridae member, rotavirus (RV), which has human epidemic impact, offering the possibility of novel intervention strategies for a human pathogen.

Protein cargo encapsulation by virus‐like particles: Strategies and applications

Viruses and the recombinant protein cages assembled from their structural proteins, known as virus-like particles (VLPs), have gained wide interest as tools in biotechnology and nanotechnology. Detailed structural information and their amenability to genetic and chemical modification make them attractive systems for further engineering. This review describes the range of non-enveloped viruses that have been co-opted for heterologous protein cargo encapsulation and the strategies that have been developed to drive encapsulation. Spherical capsids of a range of sizes have been used as platforms for protein cargo encapsulation. Various approaches, based on native and non-native interactions between the cargo proteins and inner surface of VLP capsids, have been devised to drive encapsulation. Here, we outline the evolution of these approaches, discussing their benefits and limitations. Like the viruses from which they are derived, VLPs are of interest in both biomedical and materials applications. The encapsulation of protein cargo inside VLPs leads to numerous uses in both fundamental and applied biocatalysis and biomedicine, some of which are discussed herein. The applied science of protein-encapsulating VLPs is emerging as a research field with great potential. Developments in loading control, higher order assembly, and capsid optimization are poised to realize this potential in the near future. This article is categorized under: Nanotechnology Approaches to Biology > Nanoscale Systems in Biology Biology-Inspired Nanomaterials > Protein and Virus-Based Structures.

Protein Cages: From Fundamentals to Advanced Applications

Proteins that self-assemble into polyhedral shell-like structures are useful molecular containers both in nature and in the laboratory. Here we review efforts to repurpose diverse protein cages, including viral capsids, ferritins, bacterial microcompartments, and designed capsules, as vaccines, drug delivery vehicles, targeted imaging agents, nanoreactors, templates for controlled materials synthesis, building blocks for higher-order architectures, and more. A deep understanding of the principles underlying the construction, function, and evolution of natural systems has been key to tailoring selective cargo encapsulation and interactions with both biological systems and synthetic materials through protein engineering and directed evolution. The ability to adapt and design increasingly sophisticated capsid structures and functions stands to benefit the fields of catalysis, materials science, and medicine.

Bluetongue Research at a Crossroads: Modern Genomics Tools Can Pave the Way to New Insights

Bluetongue virus (BTV) is an arthropod-borne, segmented double-stranded RNA virus that can cause severe disease in both wild and domestic ruminants. BTV evolves via several key mechanisms, including the accumulation of mutations over time and the reassortment of genome segments.Additionally, BTV must maintain fitness in two disparate hosts, the insect vector and the ruminant. The specific features of viral adaptation in each host that permit host-switching are poorly characterized. Limited field studies and experimental work have alluded to the presence of these phenomena at work, but our understanding of the factors that drive or constrain BTV's genetic diversification remains incomplete. Current research leveraging novel approaches and whole genome sequencing applications promises to improve our understanding of BTV's evolution, ultimately contributing to the development of better predictive models and management strategies to reduce future impacts of bluetongue epizootics.

Inhibition of the IFN Response by Bluetongue Virus: The Story So Far

Bluetongue virus (BTV) is the prototypical orbivirus that belongs to the Reoviridae family. BTV infection produces a disease in ruminants, particularly in sheep, that results in economic losses through reduced productivity. BTV is transmitted by the bite of Culicoides spp. midges and is nowadays distributed globally throughout subtropical and even temperate regions. As most viruses, BTV is susceptible to the IFN response, the first line of defense employed by the immune system to combat viral infections. In turn, BTV has evolved strategies to counter the IFN response and promote its replication. The present review we will revise the works describing how BTV interferes with the IFN response.

Bluetongue Virus Particles as Nanoreactors for Enzyme Delivery and Cancer Therapy

The side effects of chemotherapy can be reduced by targeting tumor cells with an enzyme (or the corresponding gene) that converts a nontoxic prodrug into a toxic drug inside the tumor cells, also killing the surrounding tumor cells via the bystander effect. Viruses are the most efficient gene delivery vehicles because they have evolved to transfer their own nucleic acids into cells, but their efficiency must be balanced against the risks of infection, the immunogenicity of nucleic acids, and the potential for genomic integration. We therefore tested the effectiveness of genome-free virus-like particles (VLPs) for the delivery of Herpes simplex virus 1 thymidine kinase (HSV1-TK), the most common enzyme used in prodrug conversion therapy. HSV1-TK is typically delivered as a gene, but in the context of VLPs, it must be delivered as a protein. We constructed VLPs and smaller core-like particles (CLPs) based on Bluetongue virus, with HSV1-TK fused to the inner capsid protein VP3. TK-CLPs and TK-VLPs could be produced in large quantities in plants. The TK-VLPs killed human glioblastoma cells efficiently in the presence of ganciclovir, with an IC₅₀ value of 14.8 μM. Conversely, CLPs were ineffective because they remained trapped in the endosomal compartment, in common with many synthetic nanoparticles. VLPs are advantageous because they can escape from endosomes and therefore allow HSV1-TK to access the cytosolic adenosine triphosphate (ATP) required for the phosphorylation of ganciclovir. The VLP delivery strategy of TK protein therefore offers a promising new modality for the treatment of cancer with systemic prodrugs such as ganciclovir.

The VP3 Protein of Bluetongue Virus Associates with the MAVS Complex and Interferes with the RIG-I-Signaling Pathway

Bluetongue virus (BTV), an arbovirus transmitted by Culicoides biting midges, is a major concern of wild and domestic ruminants. While BTV induces type I interferon (alpha/beta interferon [IFN-α/β]) production in infected cells, several reports have described evasion strategies elaborated by this virus to dampen this intrinsic, innate response. In the present study, we suggest that BTV VP3 is a new viral antagonist of the IFN-β synthesis. Indeed, using split luciferase and coprecipitation assays, we report an interaction between VP3 and both the mitochondrial adapter protein MAVS and the IRF3-kinase IKKε. Overall, this study describes a putative role for the BTV structural protein VP3 in the control of the antiviral response.

A modified lysosomal organelle mediates nonlytic egress of reovirus

Mammalian orthoreoviruses (reoviruses) are nonenveloped viruses that replicate in cytoplasmic membranous organelles called viral inclusions (VIs) where progeny virions are assembled. To better understand cellular routes of nonlytic reovirus exit, we imaged sites of virus egress in infected, nonpolarized human brain microvascular endothelial cells (HBMECs) and observed one or two distinct egress zones per cell at the basal surface. Transmission electron microscopy and 3D electron tomography (ET) of the egress zones revealed clusters of virions within membrane-bound structures, which we term membranous carriers (MCs), approaching and fusing with the plasma membrane. These virion-containing MCs emerged from larger, LAMP-1-positive membranous organelles that are morphologically compatible with lysosomes. We call these structures sorting organelles (SOs). Reovirus infection induces an increase in the number and size of lysosomes and modifies the pH of these organelles from ∼4.5-5 to ∼6.1 after recruitment to VIs and before incorporation of virions. ET of VI-SO-MC interfaces demonstrated that these compartments are connected by membrane-fusion points, through which mature virions are transported. Collectively, our results show that reovirus uses a previously undescribed, membrane-engaged, nonlytic egress mechanism and highlights a potential new target for therapeutic intervention.

Differential Localization of Structural and Non-Structural Proteins during the Bluetongue Virus Replication Cycle

Members of the Reoviridae family assemble virus factories within the cytoplasm of infected cells to replicate and assemble virus particles. Bluetongue virus (BTV) forms virus inclusion bodies (VIBs) that are aggregates of viral RNA, certain viral proteins, and host factors, and have been shown to be sites of the initial assembly of transcriptionally active virus-like particles. This study sought to characterize the formation, composition, and ultrastructure of VIBs, particularly in relation to virus replication. In this study we have utilized various microscopic techniques, including structured illumination microscopy, and virological assays to show for the first time that the outer capsid protein VP5, which is essential for virus maturation, is also associated with VIBs. The addition of VP5 to assembled virus cores exiting VIBs is required to arrest transcriptionally active core particles, facilitating virus maturation. Furthermore, we observed a time-dependent association of the glycosylated non-structural protein 3 (NS3) with VIBs, and report on the importance of the two polybasic motifs within NS3 that facilitate virus trafficking and egress from infected cells at the plasma membrane. Thus, the presence of VP5 and the dynamic nature of NS3 association with VIBs that we report here provide novel insight into these previously less well-characterized processes.

Structural nanotechnology: three-dimensional cryo-EM and its use in the development of nanoplatforms for in vitro catalysis

The organization of enzymes into different subcellular compartments is essential for correct cell function. Protein-based cages are a relatively recently discovered subclass of structurally dynamic cellular compartments that can be mimicked in the laboratory to encapsulate enzymes. These synthetic structures can then be used to improve our understanding of natural protein-based cages, or as nanoreactors in industrial catalysis, metabolic engineering, and medicine. Since the function of natural protein-based cages is related to their three-dimensional structure, it is important to determine this at the highest possible resolution if viable nanoreactors are to be engineered. Cryo-electron microscopy (cryo-EM) is ideal for undertaking such analyses within a feasible time frame and at near-native conditions. This review describes how three-dimensional cryo-EM is used in this field and discusses its advantages. An overview is also given of the nanoreactors produced so far, their structure, function, and applications.

Delivering Cargo: Plant-Based Production of Bluetongue Virus Core-Like and Virus-Like Particles Containing Fluorescent Proteins

This chapter provides a practical guide to the in planta transient production of bluetongue virus-like particles containing a fluorescent cargo protein. Bluetongue virus (BTV) particles are icosahedral, multishelled entities of a relatively large size. Heterologous expression of the four main structural proteins of BTV results in the assembly of empty virus-like particles which resemble the native virus externally, but are devoid of nucleic acid. The space within the particles is sufficient to allow incorporation of relatively large cargo proteins, such as green fluorescent protein (GFP), by genetic fusion to the structural protein VP3. The method described utilizes the pEAQ vectors for high-level transient expression of such particles in Nicotiana benthamiana.

Engineering Recombinant Virus-like Nanoparticles from Plants for Cellular Delivery

Understanding capsid assembly following recombinant expression of viral structural proteins is critical to the design and modification of virus-like nanoparticles for biomedical and nanotechnology applications. Here, we use plant-based transient expression of the Bluetongue virus (BTV) structural proteins, VP3 and VP7, to obtain high yields of empty and green fluorescent protein (GFP)-encapsidating core-like particles (CLPs) from leaves. Single-particle cryo-electron microscopy of both types of particles revealed considerable differences in CLP structure compared to the crystal structure of infection-derived CLPs; in contrast, the two recombinant CLPs have an identical external structure. Using this insight, we exploited the unencumbered pore at the 5-fold axis of symmetry and the absence of encapsidated RNA to label the interior of empty CLPs with a fluorescent bioconjugate. CLPs containing 120 GFP molecules and those containing approximately 150 dye molecules were both shown to bind human integrin via a naturally occurring Arg-Gly-Asp motif found on an exposed loop of the VP7 trimeric spike. Furthermore, fluorescently labeled CLPs were shown to interact with a cell line overexpressing the surface receptor. Thus, BTV CLPs present themselves as a useful tool in targeted cargo delivery. These results highlight the importance of detailed structural analysis of VNPs in validating their molecular organization and the value of such analyses in aiding their design and further modification.

Defeating Bluetongue virus: new approaches in the development of multiserotype vaccines

Bluetongue virus (BTV) is a global threat to domestic and wild ruminants, causing massive economic losses throughout the world. New serotypes of the virus are rapidly emerging in different continents, unfortunately there is little cross-protection between BTV serotypes. The eradication of the virus from a region is particularly complicated in areas where multiple serotypes circulate for a long time. The present review summarizes the actual concerns about the spread of the virus and relevant approaches to develop efficient vaccines against BTV, in particular those focused on a multiserotype design.

Expression of VP7, a Bluetongue virus group specific antigen by viral vectors: analysis of the induced immune responses and evaluation of protective potential in sheep

Bluetongue virus (BTV) is an economically important Orbivirus transmitted by biting midges to domestic and wild ruminants. The need for new vaccines has been highlighted by the occurrence of repeated outbreaks caused by different BTV serotypes since 1998. The major group-reactive antigen of BTV, VP7, is conserved in the 26 serotypes described so far, and its role in the induction of protective immunity has been proposed. Viral-based vectors as antigen delivery systems display considerable promise as veterinary vaccine candidates. In this paper we have evaluated the capacity of the BTV-2 serotype VP7 core protein expressed by either a non-replicative canine adenovirus type 2 (Cav-VP7 R⁰) or a leporipoxvirus (SG33-VP7), to induce immune responses in sheep. Humoral responses were elicited against VP7 in almost all animals that received the recombinant vectors. Both Cav-VP7 R⁰ and SG33-VP7 stimulated an antigen-specific CD4⁺ response and Cav-VP7 R⁰ stimulated substantial proliferation of antigen-specific CD8⁺ lymphocytes. Encouraged by the results obtained with the Cav-VP7 R⁰ vaccine vector, immunized animals were challenged with either the homologous BTV-2 or the heterologous BTV-8 serotype and viral burden in plasma was followed by real-time RT-PCR. The immune responses triggered by Cav-VP7 R⁰ were insufficient to afford protective immunity against BTV infection, despite partial protection obtained against homologous challenge. This work underscores the need to further characterize the role of BTV proteins in cross-protective immunity.

Cellular phosphoinositides and the maturation of bluetongue virus, a non-enveloped capsid virus

Background

Bluetongue virus (BTV), a member of Orbivirus genus in the Reoviridae family is a double capsid virus enclosing a genome of 10 double-stranded RNA segments. A non-structural protein of BTV, NS3, which is associated with cellular membranes and interacts with outer capsid proteins, has been shown to be involved in virus morphogenesis in infected cells. In addition, studies have also shown that during the later stages of virus infection NS3 behaves similarly to HIV protein Gag, an enveloped viral protein. Since Gag protein is known to interact with membrane lipid phosphatidylinositol (4,5) bisphosphate [PI(4,5)P₂] and one of the known binding partners of NS3, cellular protein p11 also interacts with annexin a PI(4,5)P₂ interacting protein, this study was designed to understand the role of this negatively charged membrane lipid in BTV assembly and maturation.

Methods

Over expression of cellular enzymes that either depleted cells of PI(4,5)P₂ or altered the distribution of PI(4,5)P₂, were used to analyze the effect of the lipid on BTV maturation at different times post-infection. The production of mature virus particles was monitored by plaque assay. Microscopic techniques such as confocal microscopy and electron microscopy (EM) were also undertaken to study localization of virus proteins and virus particles in cells, respectively.

Results

Initially, confocal microscopic analysis demonstrated that PI(4,5)P₂ not only co-localized with NS3, but it also co-localized with VP5, one of the outer capsid proteins of BTV. Subsequently, experiments involving depletion of cellular PI(4,5)P₂ or its relocation demonstrated an inhibitory effect on normal BTV maturation and it also led to a redistribution of BTV proteins within the cell. The data was supported further by EM visualization showing that modulation of PI(4,5)P₂ in cells indeed resulted in less particle production.

Conclusion

This study to our knowledge, is the first report demonstrating involvement of PI(4,5)P₂ in a non-enveloped virus assembly and release. As BTV does not have lipid envelope, this finding is unique for this group of viruses and it suggests that the maturation of capsid and enveloped viruses may be more closely related than previously thought.

Role of lipids on entry and exit of bluetongue virus, a complex non-enveloped virus

Non-enveloped viruses such as members of Picornaviridae and Reoviridae are assembled in the cytoplasm and are generally released by cell lysis. However, recent evidence suggests that some non-enveloped viruses exit from infected cells without lysis, indicating that these viruses may also utilize alternate means for egress. Moreover, it appears that complex, non-enveloped viruses such as bluetongue virus (BTV) and rotavirus interact with lipids during their entry process as well as with lipid rafts during the trafficking of newly synthesized progeny viruses. This review will discuss the role of lipids in the entry, maturation and release of non-enveloped viruses, focusing mainly on BTV.

Bluetongue virus outer capsid protein VP5 interacts with membrane lipid rafts via a SNARE domain

Bluetongue virus (BTV) is a nonenveloped double-stranded RNA virus belonging to the family Reoviridae. The two outer capsid proteins, VP2 and VP5, are responsible for virus entry. However, little is known about the roles of these two proteins, particularly VP5, in virus trafficking and assembly. In this study, we used density gradient fractionation and methyl beta cyclodextrin, a cholesterol-sequestering drug, to demonstrate not only that VP5 copurifies with lipid raft domains in both transfected and infected cells, but also that raft domain integrity is required for BTV assembly. Previously, we showed that BTV nonstructural protein 3 (NS3) interacts with VP2 and also with cellular exocytosis and ESCRT pathway proteins, indicating its involvement in virus egress (A. R. Beaton, J. Rodriguez, Y. K. Reddy, and P. Roy, Proc. Natl. Acad. Sci. USA 99:13154-13159, 2002; C. Wirblich, B. Bhattacharya, and P. Roy J. Virol. 80:460-473, 2006). Here, we show by pull-down and confocal analysis that NS3 also interacts with VP5. Further, a conserved membrane-docking domain similar to the motif in synaptotagmin, a protein belonging to the SNARE (soluble N-ethylmaleimide-sensitive fusion attachment protein receptor) family was identified in the VP5 sequence. By site-directed mutagenesis, followed by flotation and confocal analyses, we demonstrated that raft association of VP5 depends on this domain. Together, these results indicate that VP5 possesses an autonomous signal for its membrane targeting and that the interaction of VP5 with membrane-associated NS3 might play an important role in virus assembly.

Functional mapping of bluetongue virus proteins and their interactions with host proteins during virus replication

Bluetongue virus (BTV) is a double-stranded RNA (dsRNA) virus which is transmitted by blood-feeding gnats to wild and domestic ruminants, causing high morbidity and often high mortality. Partly due to this BTV has been in the forefront of molecular studies for last three decades and now represents one of the best understood viruses at the molecular and structural levels. BTV, like the other members of the Reoviridae family is a complex non-enveloped virus with seven structural proteins and a RNA genome consisting of 10 dsRNA segments of different sizes. In virus infected cells, three other virus encoded nonstructural proteins are synthesized. Significant recent advances have been made in understanding the structure-function relationships of BTV proteins and their interactions during virus assembly. By combining structural and molecular data it has been possible to make progress on the fundamental mechanisms used by the virus to invade, replicate in, and escape from, susceptible host cells. Data obtained from studies over a number of years have defined the key players in BTV entry, replication, assembly and egress. Specifically, it has been possible to determine the complex nature of the virion through three dimensional structure reconstructions; atomic structure of proteins and the internal capsid; the definition of the virus encoded enzymes required for RNA replication; the ordered assembly of the capsid shell and the protein sequestration required for it; and the role of three NS proteins in virus replication, assembly and release. Overall, this review demonstrates that the integration of structural, biochemical and molecular data is necessary to fully understand the assembly and replication of this complex RNA virus.

Virus trafficking - learning from single-virus tracking

What could be a better way to study virus trafficking than 'miniaturizing oneself' and 'taking a ride with the virus particle' on its journey into the cell? Single-virus tracking in living cells potentially provides us with the means to visualize the virus journey. This approach allows us to follow the fate of individual virus particles and monitor dynamic interactions between viruses and cellular structures, revealing previously unobservable infection steps. The entry, trafficking and egress mechanisms of various animal viruses have been elucidated using this method. The combination of single-virus trafficking with systems approaches and state-of-the-art imaging technologies should prove exciting in the future.

Bluetongue virus RNA binding protein NS2 is a modulator of viral replication and assembly

Background

Bluetongue virus (BTV) particles consist of seven structural proteins that are organized into two capsids. In addition, BTV also encodes three non-structural (NS) proteins of which protein 2 (NS2) is the RNA binding protein and is also the major component of virus encoded inclusion bodies (VIBs), which are believed to be virus assembly sites. To investigate the contribution of NS2 in virus replication and assembly we have constructed inducible mammalian cell lines expressing full-length NS2. In addition, truncated NS2 fragments were also generated in an attempt to create dominant negative mutants for NS2 function.

Results

Our data revealed that expression of full-length NS2 was sufficient for the formation of inclusion bodies (IBs) that were morphologically similar to the VIBs formed during BTV infection. By using either, individual BTV proteins or infectious virions, we found that while the VP3 of the inner capsid (termed as "core") that surrounds the transcription complex was closely associated with both NS2 IBs and BTV VIBs, the surface core protein VP7 co-localized with NS2 IBs only in the presence of VP3. In contrast to the inner core proteins, the outer capsid protein VP2 was not associated with either IBs or VIBs. Like the core proteins, newly synthesized BTV RNAs also accumulated in VIBs. Unlike full-length NS2, neither the amino-, nor carboxyl-terminal fragments formed complete IB structures and each appeared to interfere in overall virus replication when similarly expressed.

Conclusion

Together, these data demonstrate that NS2 is sufficient and necessary for IB formation and a key player in virus replication and core assembly. Perturbation of NS2 IB formation resulted in reduced virus synthesis and both the N terminal (NS2-1) and C terminal (NS2-2) fragments act as dominant negative mutants of NS2 function.

Interaction between Bluetongue virus outer capsid protein VP2 and vimentin is necessary for virus egress

BACKGROUND

The VP2 outer capsid protein Bluetongue Virus (BTV) is responsible for receptor binding, haemagglutination and eliciting host-specific immunity. However, the assembly of this outer capsid protein on the transcriptionally active viral core would block transcription of the virus. Thus assembly of the outer capsid on the core particle must be a tightly controlled process during virus maturation. Earlier studies have detected mature virus particles associated with intermediate filaments in virus infected cells but the viral determinant for this association and the effect of disrupting intermediate filaments on virus assembly and release are unknown.

RESULTS

In this study it is demonstrated that BTV VP2 associates with vimentin in both virus infected cells and in the absence of other viral proteins. Further, the determinants of vimentin localisation are mapped to the N-terminus of the protein and deletions of amino acids between residues 65 and 114 are shown to disrupt VP2-vimentin association. Site directed mutation also reveals that amino acid residues Gly 70 and Val 72 are important in the VP2-vimentin association. Mutation of these amino acids resulted in a soluble VP2 capable of forming trimeric structures similar to unmodified protein that no longer associated with vimentin. Furthermore, pharmacological disruption of intermediate filaments, either directly or indirectly through the disruption of the microtubule network, inhibited virus release from BTV infected cells.

CONCLUSION

The principal findings of the research are that the association of mature BTV particles with intermediate filaments are driven by the interaction of VP2 with vimentin and that this interaction contributes to virus egress. Furthermore, i) the N-terminal 118 amino acids of VP2 are sufficient to confer vimentin interaction. ii) Deletion of amino acids 65-114 or mutation of amino acids 70-72 to DVD abrogates vimentin association. iii) Finally, disruption of vimentin structures results in an increase in cell associated BTV and a reduction in the amount of released virus from infected cells.