Molecular characterization of Bombyx mori cytoplasmic polyhedrosis virus genome segment 4

Biological and genomic characterization of a cypovirus isolated from golden muga silkworm, Antheraea assamensis Helfer (Lepidoptera: Saturniidae)

A potential viral pathogen, cypovirus causing cytoplasmic polyhedrosis in the Indian golden muga silkworm, Antheraea assamensis Helfer, was isolated and characterized. Electron microscopy analysis confirmed the presence of typical occlusion bodies with icosahedral virions embedded in polyhedral matrices. The viral genome was dsRNA totaling approximately 24.9 kb in size, divided into 10 discrete segments containing one single open reading frame (ORF) each. Genomic analysis revealed conserved non-coding sequences such as 'AGUAAU' and 'AUAGAGC' at 5' and 3' termini, respectively. Functional annotation identified the presence of structural proteins, such as major and minor capsid proteins, as well as enzymatic proteins, including RNA-dependent RNA polymerase (RdRp). Phylogenetic analysis using deduced amino acid sequences of viral RdRp gene indicated a close evolutionary relationship between the cypovirus isolated from Antheraea assamensis and Antheraea mylitta cypovirus 4 (AmCPV4), thus we named the Indian golden muga silkworm cypovirus as Antheraea assamensis cypovirus 4 (AaCPV4). Nevertheless, AaCPV4 does not have a genomic segment 11 which was earlier reported in AmCPV4. Bioassay studies demonstrated high virulence, with 100 % larval mortality observed within 12 days of infection due to cytoplasmic polyhedrosis. Tissue tropism studies revealed significant viral replication in the midgut, hemolymph, and malpighian tubules, with the midgut exhibiting the highest viral load (9.65 log copy number of RdRp gene/µg of RNA). Cross-transmission experiments demonstrated AaCPV4 host specificity, infecting only in Antheraea species (A. mylitta and A. assamensis), while other lepidopteran insects including silkworms Bombyx mori, and Samia ricini were not susceptible to AaCPV4 infection. According to morphological, genetic, and biological characteristics, we suggest that AaCPV4 is an isolate of the species Cypovirus antheraeae (family Spinareoviridae).

Polyhedrin microcrystals embedded with bFGF promote wound healing

Growth factors play a critical role in wound healing, and finding a suitable biosustained-release system has always been a research hotspot. Bombyx mori cypovirus (BmCPV) is an insect virus, which produces polyhedra that encapsulate progeny virions. In this study, we found that the viral structural protein VP7 encoded by the BmCPV genomic dsRNAs S7 segment can interact with polyhedrin (Polh) encoded by the BmCPV genomic dsRNAs S10 segment. We also confirmed that the amino acid sequence at position 331-360 (VP7-tag) of VP7 is needed to interact with Polh. We found that VP7-tag can be used as an immobilization signal to direct the incorporation of foreign proteins into polyhedra. Furthermore, we constructed polyhedra (bFGF-polyhedra) containing basic fibroblast growth factor (bFGF) using a baculovirus expression system co-expressing Polh and bFGF-VP7 (fusion of VP7-tag to C-terminus of bFGF). We found that bFGF-VP7 embedded into polyhedra was difficult to degrade in the natural environment, and bFGF-VP7 was continuously released from the polyhedra, enhancing cell proliferation and migration. The animal model was used to assess the effect of bFGF-polyhedra spray on the healing of full-thickness wounds. bFGF-polyhedra promoted the expression of TGF-β1, α-SMA, and PCNA, inhibited the expression of proinflammatory factors NF-κB and COX-2, promoted the proliferation and differentiation of fibroblasts, enhanced collagen production and epidermal regeneration, and improved wound healing. These results indicated that bFGF-polyhedra has a promising potential for accelerating wound healing.

Development of a cypovirus protein microcrystal-encapsulated Bacillus thuringiensis UV-tolerant and mosquitocidal δ-endotoxin

The δ-endotoxin Cry4Aa from Bacillus thuringiensis israelensis (Bti) has insecticidal characteristics specific to insects of the order Diptera. Although Cry4Aa has shown potential as an effective proteinaceous pesticide against mosquitoes, it has an ultraviolet (UV)-intolerant property that limits its outdoor use. Our previous research showed that protein microcrystal polyhedra from Bombyx mori cypovirus can encapsulate diverse foreign proteins and maintain long-term protein activity under hostile environmental conditions, including UV irradiation. In this study, we report the development of polyhedra encapsulating the Cry4Aa insecticidal activity domain by using a modified baculovirus expression system. We confirmed the oral intake of recombinant polyhedra introduced into the experimental environment by the larvae of a mosquito, Aedes albopictus, and delivery of encapsulated proteins into the digestive tract. The polyhedra encapsulating partial Cry4Aa showed mosquito larvicidal activity during incubation of larvae with 50% lethal-dose value of 23.717×10⁴ cubes for 10 Aedes albopictus larvae in 1 ml water. In addition, polyhedra showed a specific property to reduce the impact of UV-C irradiation on the activity of encapsulated partial Cry4Aa, thus demonstrating the effectiveness of encapsulating Bti δ-endotoxins inside polyhedra to increase the availability of proteinaceous pesticides for outdoor use for mosquito control.

Bridging the electrode-neuron gap: finite element modeling of in vitro neurotrophin gradients to optimize neuroelectronic interfaces in the inner ear

Although cochlear implant (CI) technology has allowed for the partial restoration of hearing over the last few decades, persistent challenges (e.g., poor performance in noisy environments and limited ability to decode intonation and music) remain. The "electrode-neuron gap" is inherent to these challenges and poses the most significant obstacle to advancing past the current plateau in CI performance. We propose the development of a "neuro-regenerative nexus"-a biological interface that doubly preserves native spiral ganglion neurons (SGNs) while precisely directing the growth of neurites arising from transplanted human pluripotent stem cell (hPSC)-derived otic neuronal progenitors (ONPs) toward the native SGN population. We hypothesized that the Polyhedrin Delivery System (PODS®-recombinant human brain-derived neurotrophic factor [rhBDNF]) could stably provide the adequate BDNF concentration gradient to hPSC-derived late-stage ONPs to facilitate otic neuronal differentiation and directional neurite outgrowth. To test this hypothesis, a finite element model (FEM) was constructed to simulate BDNF concentration profiles generated by PODS®-rhBDNF based on initial concentration and culture device geometry. For biological validation of the FEM, cell culture experiments assessing survival, differentiation, neurite growth direction, and synaptic connections were conducted using a multi-chamber microfluidic device. We were able to successfully generate the optimal BDNF concentration gradient to enable survival, neuronal differentiation toward SGNs, directed neurite extension of hPSC-derived SGNs, and synaptogenesis between two hPSC-derived SGN populations. This proof-of-concept study provides a step toward the next generation of CI technology. STATEMENT OF SIGNIFICANCE: Our study demonstrates that the generation of in vitro neurotrophin concentration gradients facilitates survival, neuronal differentiation toward auditory neurons, and directed neurite extension of human pluripotent stem cell-derived auditory neurons. These findings are indispensable to designing a bioactive cochlear implant, in which stem cell-derived neurons are integrated into a cochlear implant electrode strip, as the strategy will confer directional neurite growth from the transplanted cells in the inner ear. This study is the first to present the concept of a "neuro-regenerative nexus" congruent with a bioactive cochlear implant to eliminate the electrode-neuron gapthe most significant barrier to next-generation cochlear implant technology.

Effects of transgenic silk materials that incorporate FGF-7 protein microcrystals on the proliferation and differentiation of human keratinocytes

The silk glands of silkworms produce large quantities of fibroin, which is a protein that can be physically processed and used as a biodegradable carrier for cell growth factors in tissue engineering applications. Meanwhile, protein microcrystals known as polyhedra, which are derived from cypovirus 1, have been used as a vehicle to protect and release encapsulated cell growth factors. We report the generation of transgenic silkworms that express recombinant fibroblast growth factor-7 (FGF-7) fused with the polyhedron-encapsulating signal in polyhedra produced in the middle (MSG) and posterior (PSG) silk glands. Immunofluorescence showed that polyhedra from silk glands are associated with FGF-7. The MSG and PSG from transgenic silkworms were processed into fine powdery materials, from which FGF-7 activity was released to stimulate the proliferation of human keratinocyte epidermal cells. Powders from PSGs exhibited higher FGF-7 activity than those from MSGs. Moreover, PSG powder showed a gradual release of FGF-7 activity over a long period and induced keratinocyte proliferation and differentiation in 3D culture to promote the formation of stratified epidermis expressing positive differentiation marker proteins. Our results indicate that powdery materials incorporating the FGF-7-polyhedra microcrystals from silk glands are valuable for developing cell/tissue engineering applications in vivo and in vitro.

An engineered three-dimensional stem cell niche in the inner ear by applying a nanofibrillar cellulose hydrogel with a sustained-release neurotrophic factor delivery system

Although the application of human embryonic stem cells (hESCs) in stem cell-replacement therapy remains promising, its potential is hindered by a low cell survival rate in post-transplantation within the inner ear. Here, we aim to enhance the in vitro and in vivo survival rate and neuronal differentiation of otic neuronal progenitors (ONPs) by generating an artificial stem cell niche consisting of three-dimensional (3D) hESC-derived ONP spheroids with a nanofibrillar cellulose hydrogel and a sustained-release brain-derivative neurotrophic factor delivery system. Our results demonstrated that the transplanted hESC-derived ONP spheroids survived and neuronally differentiated into otic neuronal lineages in vitro and in vivo and also extended neurites toward the bony wall of the cochlea 90 days after the transplantation without the use of immunosuppressant medication. Our data in vitro and in vivo presented here provide sufficient evidence that we have established a robust, reproducible protocol for in vivo transplantation of hESC-derived ONPs to the inner ear. Using our protocol to create an artificial stem cell niche in the inner ear, it is now possible to work on integrating transplanted hESC-derived ONPs further and also to work toward achieving functional auditory neurons generated from hESCs. Our findings suggest that the provision of an artificial stem cell niche can be a future approach to stem cell-replacement therapy for inner-ear regeneration. STATEMENT OF SIGNIFICANCE: Inner ear regeneration utilizing human embryonic stem cell-derived otic neuronal progenitors (hESC-derived ONPs) has remarkable potential for treating sensorineural hearing loss. However, the local environment of the inner ear requires a suitable stem cell niche to allow hESC-derived ONP engraftment as well as neuronal differentiation. To overcome this obstacle, we utilized three-dimensional spheroid formation (direct contact), nanofibrillar cellulose hydrogel (extracellular matrix), and a neurotrophic factor delivery system to artificially create a stem cell niche in vitro and in vivo. Our in vitro and in vivo data presented here provide sufficient evidence that we have established a robust, reproducible protocol for in vivo transplantation of hESC-derived ONPs to the inner ear.

New method for immobilising diverse proteins onto cubic micro-protein polyhedrin crystals

Cypovirus is an insect virus that is encapsulated in stable cubic protein crystals composed of polyhedrin protein produced in virus-infected cells. Molecular technology developed over the last decade is now able to immobilise proteins of interest on polyhedrin crystals. Modified polyhedrin crystals can be used in cell cultures for implantation in animals and vaccines, among other applications. However, this technique does not work for some proteins. Here, we developed and tested an alternative approach for immobilising foreign proteins in polyhedrin crystals using a linker method; diverse proteins, such as fluorescent proteins, enzymes, antibodies, and streptavidin were successfully contained. The immobilised antibodies retained their binding activity on filter paper, implying their potential for new immunochromatography applications. Moreover, this immobilisation method allows enzymes to be collected from one reaction reagent and transferred to another reagent. These results demonstrate the potential of this immobilisation method and the likelihood of expanding the applications of polyhedrin crystals using this approach.

Raman spectroscopy insight into Norovirus encapsulation in Bombyx mori cypovirus cubic microcrystals

Protein and amino acid structures of Norovirus-like particles (NoVLP) have been investigated by Raman spectroscopy before and after encapsulation into Bombyx mori cypovirus (BmCPV) cubic microcrystals, which are usually referred to as cubes or polyhedra. Two different types of tag were used in co-expression, namely VP3 and H1 tags. VP3 tag is derived from a capsid protein VP4 from BmCPV and H1 tag is N-terminal α-helix of BmCPV polyhedrin, respectively. A major capsid protein VP1 of NoVLP G11.4 was fused with H1 or VP3 tags, and then encapsulated into BmCPV polyhedra. Analyses of the spectroscopic data permitted the assignment of conformation-sensitive Raman bands to viral amino acid constituents and the observation of structural similarities or differences between differently tagged samples. Three separate Raman zones were attentioned, namely, the ring-mode structure region (1000-1500 cm^-1), the CO and CC double-bond region and its surroundings (1500-1750 cm^-1), and the high-frequency CH stretching region (2800-3100 cm^-1). Structural fingerprints could be found in specific spectral zones for differently co-expressed samples. One clear characteristic of the H1-tagged VP1 polyhedra was the increase in tyrosine fraction, which played a critical role in binding neighboring strands through its unpaired negatively charged COO^- sites. This feature could consistently be detected in different regions, but it was best represented by Raman signals associated with negatively charged COO^- sites and H1 helices in the double-bond region. Such peculiar chemical features were revealed by two relatively broad bands at 1570 and 1630 cm^-1, which were assigned to COO^- anti-symmetric stretching and amide I in 3₁₀-helix extensions to α-helices at N-termini, respectively. These specific features did not display in the spectrum of the VP3-tagged VP1 polyhedra. Concurrently, a strong reduction of CH bond Raman signal was noticed in the high frequency stretching region of the Raman spectrum upon H1-tagged VP1 polyhedra. The Raman activity most strikingly also represented fingerprints of tagged NoVLP VP1 after its encapsulation into BmCPV polyhedra, opening thus the possibility to in situ advanced experiments in the fields of drug delivery and regenerative medicine.

3D co-cultures of keratinocytes and melanocytes and cytoprotective effects on keratinocytes against reactive oxygen species by insect virus-derived protein microcrystals

Stable protein microcrystals called polyhedra are produced by certain insect viruses. Cytokines, such as fibroblast growth factors (FGFs), can be immobilized within polyhedra. Here, we investigated three-dimensional (3D) co-cultures of keratinocytes and melanocytes on collagen gel containing FGF-2 and FGF-7 polyhedra. Melanocytes were observed to reside at the base of the 3D cell culture and melanin was also typically observed in the lower layer. The 3D cell culture model with FGF-2 and FGF-7 polyhedra was a useful in vitro model of the epidermis due to effective melanogenesis, proliferation and differentiation of keratinocytes. FGF-7 polyhedra showed a potent cytoprotective effect when keratinocytes were treated with menadione, which is a generator of reactive oxygen species. The cytoprotective effect was activated by the inositol triphosphate kinase-Akt pathway leading to upregulation of the antioxidant enzymes superoxide dismutase and peroxiredoxin 6.

Interactions among Dendrolimus punctatus cypovirus proteins and identification of the genomic segment encoding its A-spike

Revealing the interactions among cypovirus proteins would facilitate our understanding of the replication and assembly of this virus. In the present study, interactions among proteins encoded by the 10 segments of Dendrolimus punctatus cypovirus (DpCPV) were identified using yeast two-hybrid (Y2H) and far-Western blotting assays. In total, 24 pairs of interactions were detected. Twelve pairs of one-direction interactions, four pairs of binary interactions and four pairs of self-associations were identified in the Y2H assays. Another four pairs of interactions were identified by far-Western blotting. The interactions between the methyltransferase domain of the turret protein (VP3) and VP4 as well as between polyhedrin and VP4 were further confirmed by far-Western blotting and pull-down assays, respectively. In addition, immunogold labelling showed that the A-spike of DpCPV is formed by VP4. In conclusion, we obtained a protein-protein interaction network of DpCPV and showed that its A-spike is formed by VP4 encoded by genomic segment 6.

Genome segment 5 of Antheraea mylitta cytoplasmic polyhedrosis virus encodes a bona fide guanylyltransferase

BACKGROUND

Antheraea mylitta cytoplasmic polyhedrosis virus (AmCPV), a cypovirus of Reoviridae family, infects non mulberry Indian silk worm, Antheraea mylitta, and contains eleven segmented double stranded RNA in its genome (S1-S11). Some of its genome segments (S1-S3, and S6-S11) have been previously characterized but genome segment encoding the viral guanylyltransferase which helps in RNA capping has not been characterized.

RESULTS

In this study genome segment 5 (S5) of AmCPV was converted to cDNA, cloned and sequenced. S5 consisted of 2180 nucleotides, with one long ORF of 1818 nucleotides and could encode a protein of 606 amino acids with molecular mass of ~65 kDa (p65). Bioinformatics analysis showed presence of KLRS and HxnH motifs as observed in some other reoviral guanylyltransferase and suggests that S5 may encodes viral guanylyltransferase. The ORF of S5 was expressed in E. coli as 65 kDa his tagged fusion protein, purified through Ni-NTA chromatography and polyclonal antibody was raised. Immunoblot analysis of virion particles with the purified antibody showed specific immunoreactive band and suggests p65 as a viral structural protein. Functional analysis showed that recombinant p65 possesses guanylyltransferase activity, and transfers GMP moiety to the 5' diphosphate (A/G) ended viral RNA after the formation of p65-GMP complex for capping. Kinetic analysis showed K(m) of this enzyme for GTP and RNA was 34.24 uM and 98.35 nM, respectively. Site directed mutagenesis at K21A in KLRS motif, and H93A or H105A in HxnH motif completely abolished the autoguanylylation activity and indicates importance of these residues at these sites. Thermodynamic analysis showed p65-GTP interaction was primarily driven by enthalpy (ΔH = -399.1 ± 4.1 kJ/mol) whereas the p65-RNA interaction by favorable entropy (0.043 ± 0.0049 kJ/ mol).

CONCLUSION

Viral capping enzymes play a critical role in the post transcriptional or post replication modification in case of RNA virus. Our results of cloning, sequencing and functional analysis of AmCPV S5 indicates that S5 encoded p65 through its guanylyltransferase activity can transfer guanine residue to the 5' end of viral RNA for capping. Further studies will help to understand complete capping process of cypoviral RNA during viral replication within the viral capsid.

Nonvirus encoded proteins could be embedded into Bombyx mori cypovirus polyhedra

To explore whether the nonvirus encoded protein could be embedded into Bombyx mori cypovirus (BmCPV) polyhedra. The stable transformants of BmN cells expressing a polyhedrin (Polh) gene of BmCPV were constructed by transfection with a non-transposon derived vector containing a polh gene. The polyhedra were purified from the midguts of BmCPV-infected silkworms and the transformed BmN cells, respectively. The proteins embedded into polyhedra were determined by mass spectrometry analysis. Host derived proteins were detected in the purified polyhedra. Analysis of structure and hydrophilicity of embedded proteins indicated that the hydrophilic proteins, in structure, were similar to the left-handed structure of polyhedrin or the N-terminal domain of BmCPV structural protein VP3, which were easily embedded into the BmCPV polyhedra. The lysate of polyhedra purified from the infected transformation of BmN cells with modified B. mori baculovirus BmPAK6 could infect BmN cells, indicating that B. mori baculovirus could be embedded into BmCPV polyhedra. Both the purified polyhedra and its lysate could be coloured by X-gal, indicating that the β-galactosidase expressed by BmPAK6 could be incorporated into BmCPV polyhedra. These results suggested that some heterologous proteins and baculovirus could be embedded into polyhedra in an unknown manner.

Control of angiogenesis by VEGF and endostatin-encapsulated protein microcrystals and inhibition of tumor angiogenesis

Encapsulation of cytokines within protein microcrystals (polyhedra) is a promising approach for the stabilization and delivery of therapeutic proteins. Here, we investigate the influence of vascular endothelial growth factor (VEGF) microcrystals and endostatin microcrystals on angiogenesis. VEGF was successfully encapsulated into microcrystals derived from insect cypovirus with overexpression of protein disulfide bond isomerase. VEGF microcrystals were observed to increase the phosphorylation of p42/p44 MAP kinase and to stimulate the proliferation, migration, and network and tube formation of human umbilical vein endothelial cells (HUVECs). Endostatin was also successfully encapsulated into microcrystals. Endostatin microcrystals showed antiangiogenesis activities and inhibited the migration, and network and tube formation of HUVECs. Local administration of endostatin microcrystals in mice inhibited both angiogenesis and tumor growth with clear significant differences between treatment and control groups. Endostatin microcrystals only affected angiogenesis, but had no significant effect on lymphangiogenesis compared to controls. Local therapy using endostatin microcrystals offers a potential approach to achieve sustained therapeutic release of antiangiogenic molecules for cancer treatment.

Characterization of the complete genome segments from BmCPV-SZ, a novelBombyx moricypovirus 1 isolate

A novel Bombyx mori cypovirus 1 isolated from infected silkworm larvae and tentatively assigned as Bombyx mori cypovirus 1 isolate Suzhou (BmCPV-SZ). The complete nucleotide sequences of genomic segments S1–S10 from BmCPV-SZ were determined. All segments possessed a single open reading frame; however, bioinformatic evidence suggested a short overlapping coding sequence in S1. Each BmCPV-SZ segment possessed the conserved terminal sequences AGUAA and GUUAGCC at the 5′ and 3′ ends, respectively. The conserved A/G at the –3 position in relation to the AUG codon could be found in the BmCPV-SZ genome, and it was postulated that this conserved A/G may be the most important nucleotide for efficient translation initiation in cypoviruses (CPVs). Examination of the putative amino acid sequences encoded by BmCPV-SZ revealed some characteristic motifs. Homology searches showed that viral structural proteins VP1, VP3, and VP4 had localized homologies with proteins of Rice ragged stunt virus , a member of the genus Oryzavirus within the family Reoviridae. A phylogenetic tree based on RNA-dependent RNA polymerase sequences demonstrated that CPV is more closely related to Rice ragged stunt virus and Aedes pseudoscutellaris reovirus than to other members of Reoviridae, suggesting that they may have originated from common ancestors.

Insect virus polyhedra, infectious protein crystals that contain virus particles

High-resolution atomic structures have been reported recently for two types of viral polyhedra, intracellular protein crystals produced by ubiquitous insect viruses. Polyhedra contain embedded virus particles and function as the main infectious form for baculoviruses and cypoviruses, two distinct classes of viruses that infect mainly Lepitoptera species (butterflies and moths). Polyhedra are extremely stable and protect the virus particles once released in the environment. The extensive crystal contacts observed in the structures explain the remarkable stability of viral polyhedra and provide hints about how these crystals dissolve in the alkaline midgut, releasing embedded virus particles to infect feeding larvae. The stage is now set to answer intriguing questions about the in vivo crystallization of polyhedra, how virus particles are incorporated into polyhedra, and what determines the size and shape of the crystals. Large quantities of polyhedra can be obtained from infected larvae and polyhedra can also be produced using insect cell expression systems. Modified polyhedra encapsulating other entities in place of virus particles have potential applications as a means to stabilize proteins such as enzymes or growth factors, and the extremely stable polyhedrin lattice may provide a framework for future engineered micro-crystal devices.

Electron tomography reveals polyhedrin binding and existence of both empty and full cytoplasmic polyhedrosis virus particles inside infectious polyhedra

Previous studies have described the structure of purified cytoplasmic polyhedrosis virus (CPV) and that of polyhedrin protein. However, how polyhedrin molecules embed CPV particles inside infectious polyhedra is not known. By using electron tomography, we show that CPV particles are occluded within the polyhedrin crystalline lattice with a random spatial distribution and interact with the polyhedrin protein through the A-spike rather than as previously thought through the B-spike. Furthermore, both full (with RNA) and empty (no RNA) capsids were found inside polyhedra, suggesting a spontaneous RNA encapsidating process for CPV assembly in vivo.

Structure-based targeting of bioactive proteins into cypovirus polyhedra and application to immobilized cytokines for mammalian cell culture

Certain insect viruses produce stable infectious micro-crystals called polyhedra which function to protect the virus after the death of infected larvae. Polyhedra form within infected cells and contain numerous virus particles embedded in a crystalline lattice of the viral protein polyhedrin. We have previously demonstrated that the N-terminal 75 amino acids of the Bombx mori cypovirus (BmCPV) turret protein (VP3) can function as a polyhedrin recognition signal leading to the incorporation of foreign proteins into polyhedra. Foreign proteins tagged with the VP3 polyhedrin recognition signal were incorporated into polyhedra by co-expression with polyhedrin in insect cells. We have used this method to encapsulate a wide variety of foreign proteins into polyhedra. The atomic structure of BmCPV polyhedrin showed that the N-terminal H1 alpha-helix of polyhedrin plays a significant role in cross-linking and stabilizing polyhedra. Here we show that the polyhedrin H1-helix can also function as a polyhedrin recognition signal and can be used like the VP3 N-terminal sequence to target foreign proteins into polyhedra. In addition, the two targeting methods can be used together to produce polyhedra containing both EGFP and Discosoma sp. Red Fluorescent Protein (DsRed). The modified polyhedra were imaged using dual-wavelength confocal microscopy showing that the two foreign proteins are uniformly incorporated into polyhedra at similar levels. We have investigated the biological and physiological properties of fibroblast growth factor-2 (FGF-2), FGF-7 and epidermal growth factor (EGF) immobilized on polyhedra with either the H1 or the VP3 tag. Growth factors produced by both methods were functional, inducing the growth of fibroblast cells and keratinocytes. The results demonstrate the utility and flexibility of modified polyhedra for encapsulating and stabilizing bioactive proteins.

The effect of transmission route on plant virus epidemic development and disease control

A model for indirect vector transmission and epidemic development of plant viruses is extended to consider direct transmission through vector mating. A basic reproduction number is derived which is the sum of the R(0) values specific for three transmission routes. We analyse the model to determine the effect of direct transmission on plant disease control directed against indirect transmission. Increasing the rate of horizontal sexual transmission means that vector control rate or indirect transmission rate must be increased/decreased substantially to maintain R(0) at a value less than 1. By contrast, proportionately increasing the probability of transovarial transmission has little effect. Expressions are derived for the steady-state values of the viruliferous vector population. There is clear advantage for an insect virus in indirect transmission to plants, especially where the sexual and transovarial transmission rates are low; however information on virulence-transmissibility relationships is required to explain the evolution of a plant virus from an insect virus.

3.88 A structure of cytoplasmic polyhedrosis virus by cryo-electron microscopy

Cytoplasmic polyhedrosis virus (CPV) is unique within the Reoviridae family in having a turreted single-layer capsid contained within polyhedrin inclusion bodies, yet being fully capable of cell entry and endogenous RNA transcription. Biochemical data have shown that the amino-terminal 79 residues of the CPV turret protein (TP) is sufficient to bring CPV or engineered proteins into the polyhedrin matrix for micro-encapsulation. Here we report the three-dimensional structure of CPV at 3.88 A resolution using single-particle cryo-electron microscopy. Our map clearly shows the turns and deep grooves of alpha-helices, the strand separation in beta-sheets, and densities for loops and many bulky side chains; thus permitting atomic model-building effort from cryo-electron microscopy maps. We observed a helix-to-beta-hairpin conformational change between the two conformational states of the capsid shell protein in the region directly interacting with genomic RNA. We have also discovered a messenger RNA release hole coupled with the mRNA capping machinery unique to CPV. Furthermore, we have identified the polyhedrin-binding domain, a structure that has potential in nanobiotechnology applications.

Towards atomic resolution structural determination by single-particle cryo-electron microscopy

Recent advances in cryo-electron microscopy and single-particle reconstruction (collectively referred to as 'cryoEM') have made it possible to determine the three-dimensional (3D) structures of several macromolecular complexes at near-atomic resolution ( approximately 3.8-4.5A). These achievements were accomplished by overcoming the challenges in sample handling, instrumentation, image processing, and model building. At near-atomic resolution, many detailed structural features can be resolved, such as the turns and deep grooves of helices, strand separation in beta sheets, and densities for loops and bulky amino acid side chains. Such structural data of the cytoplasmic polyhedrosis virus (CPV), the Epsilon 15 bacteriophage and the GroEL complex have provided valuable constraints for atomic model building using integrative tools, thus significantly enhancing the value of the cryoEM structures. The CPV structure revealed a drastic conformational change from a helix to a beta hairpin associated with RNA packaging and replication, coupling of RNA processing and release, and the long sought-after polyhedrin-binding domain. These latest advances in single-particle cryoEM provide exciting opportunities for the 3D structural determination of viruses and macromolecular complexes that are either too large or too heterogeneous to be investigated by conventional X-ray crystallography or nuclear magnetic resonance (NMR) methods.

The complete nucleotide sequence of the type 5 Helicoverpa armigera cytoplasmic polyhedrosis virus genome

The S1-6, S8, and S9 segments of the type 5 Helicoverpa armigera cytoplasmic polyhedrosis virus (HaCPV-5, Chinese strain) were cloned and sequenced, completing the HaCPV-5 genome. We found that each HaCPV-5 segment exhibits the conserved terminal sequences AGUU and UUGC located at the 5' and 3' ends, respectively. We also analyzed the translation initiation codon of the HaCPV-5 genome and compared it with the available cypovirus sequences in GenBank. We postulated that the conserved purine at the -3 position in relation to the AUG codon is probably the most important nucleotide for efficient translation initiation in cypovirus. Although the nucleotide sequences of the HaCPV-5 segments S1-10 exhibit no significant similarity to other viruses, blast searches did reveal some similarities between predicted HaCPV-5 amino acid sequences and those of other viruses.

Immobilization of bioactive fibroblast growth factor-2 into cubic proteinous microcrystals (Bombyx mori cypovirus polyhedra) that are insoluble in a physiological cellular environment

The supramolecular architecture of the extracellular matrix and the disposition of its specific accessory molecules give rise to variable heterotopic signaling cues for single cells. Here we have described the successful occlusion of human fibroblast growth factor-2 (FGF-2) into the cubic inclusion bodies (FGF-2 polyhedra) of the Bombyx mori cytoplasmic polyhedrosis virus (BmCPV). The polyhedra are proteinous cubic crystals of several microns in size that are insoluble in the extracellular milieu. Purified FGF-2 polyhedra were found to stimulate proliferation and phosphorylation of p44/p42 mitogen-activated protein kinase in cultured fibroblasts. Moreover, cellular responses were blocked by a synthetic inhibitor of the FGF signaling pathway, SU5402, suggesting that FGF-2 polyhedra indeed act through FGF receptors. Furthermore, FGF-2 polyhedra retained potent growth stimulatory properties even after desiccation. We have demonstrated that BmCPV polyhedra microcrystals that occlude extracellular signaling proteins are a novel and versatile tool that can be employed to analyze cellular behavior at the single cell level.

Phylogenetic analysis of Heliothis armigera cytoplasmic polyhedrosis virus type 14 and a series of dwarf segments found in the genome

Full-length nucleotide sequences for the genome segments (S1-S6) of Heliothis armigera cytoplasmic polyhedrosis virus type 14 (HaCPV-14) have been characterized. Each segment consists of a single open reading frame with conserved motifs AGAA and AGCU at the 5' and 3' ends, respectively. Comparison of the proteins of HaCPV-14 with those of other members of the family Reoviridae suggests that S1 encodes an RNA-dependent RNA polymerase (RdRp), whilst S2 encodes a major capsid protein of the virus. Phylogenetic analysis of RdRps from 16 viruses in the family Reoviridae reveals that the genera Cypovirus and Oryzavirus may have originated from a common insect virus ancestor. A series of viable dwarf segments originating from S5 of HaCPV-14 has been identified. Analysis of the predicted secondary structures for these dwarf segments suggests that the signals essential for replication and packaging are located within the terminal sequences of these segments.

Baculovirus expression of the 11 mycoreovirus-1 genome segments and identification of the guanylyltransferase-encoding segment

The type member Mycoreovirus 1 (MyRV-1) of a newly described genus, Mycoreovirus, isolated from a hypovirulent strain 9B21 of the chestnut blight fungus, has a genome composed of 11 dsRNA segments (S1-S11). All of the segments have single ORFs on their capped, positive-sense strands. Infection of insect cells by baculovirus recombinants carrying full-length cDNAs of S1-S11 resulted in overexpression of protein products of the expected sizes, based on their deduced amino acid sequences. This expression system was utilized to identify the S3-encoded protein (VP3) as a guanylyltransferase by an autoguanylylation assay, in which only VP3 was radiolabelled with [alpha-(32)P]GTP. A series of progressive N-terminal and C-terminal deletion mutants was made to localize the autoguanylylation-active site of VP3 to aa residues 133-667. Within this region, a sequence stretch (aa 170-250) with relatively high sequence similarity to homologues of two other mycoreoviruses and two coltiviruses was identified. Site-directed mutagenesis of conserved aa residues revealed that H233, H242, Y243, F244 and F246, but not K172 or K202, play critical roles in guanylyltransferase activities. Together with broader sequence alignments of 'turreted' reoviruses, these results supported the a/vxxHx(8)Hyf/lvf motif, originally noted for orthoreovirus and aquareoviruses, as an active site for guanylyltransferases of viruses within the Orthoreovirus, Aquareovirus, Cypovirus, Oryzavirus, Fijivirus, Coltivirus and Mycoreovirus genera, as well as for the proposed Dinovernavirus genus.

Nondestructive micro-patterning of proteinous occlusion bodies in water by femtosecond laser-induced mechanical force

Some insect virus produces proteinous occlusion bodies named polyhedra, on which it is possible to immobilize functional proteins, such as green fluorescent proteins, antibodies, and growth factors, with keeping their biological activity. In this work, several kinds of polyhedra were micro-patterned by applying a mechanical force induced by femtosecond laser irradiation of a water buffer. In the printing process, since the laser is not directly irradiated on polyhedra, damages of polyhedra due to dryness and photothermal and photochemical reactions will be suppressed. The ability of the pattering was demonstrated by micro-sized checkerboard pattern, on which polyhedra with and without occluding enhanced green fluorescent protein were sorted. Furthermore, it was indicated that polyhedra are available as a scaffold of animal cell. This patterning method will be a promising technique to realize a microdevice in which functions of cell are artistically activated.

Identification and genome characterization of Heliothis armigera cypovirus types 5 and 14 and Heliothis assulta cypovirus type 14

Genomic characterization of Heliothis armigera cypovirus (HaCPV) isolated from China showed that insects were co-infected with several cypoviruses (CPVs). One of the CPVs (HaCPV-5) could be separated from the others by changing the rearing conditions of the Heliothis armigera larvae. This finding was further confirmed by nucleotide sequencing analysis. Genomic sequences of segments S10-S7 from HaCPV-14, S10 and S7 from HaCPV-5, and S10 from Heliothis assulta CPV-14 were compared. Results from database searches showed that the nucleotide sequences and deduced amino acid sequences of the newly identified CPVs had high levels of identity with those of reported CPVs of the same type, but not with CPVs of different types. Putative amino acid sequences of HaCPV-5 S7 were similar to that of the protein from Rice ragged stunt virus (genus Oryzavirus, family Reoviridae), suggesting that CPVs and oryzaviruses are related more closely than other genera of the family Reoviridae. Conserved motifs were also identified at the ends of each RNA segment of the same virus type: type 14, 5'-AGAAUUU...CAGCU-3'; and type 5, 5'-AGUU...UUGC-3'. Our results are consistent with classification of CPV types based on the electrophoretic patterns of CPV double-stranded RNA.

Immobilization of diverse foreign proteins in viral polyhedra and potential application for protein microarrays

Cypoviruses are insect viruses that produce a cytoplasmic crystalline particle called the polyhedron in which progeny virions are occluded. The virion structural protein, VP3, is implicated in the occlusion of viral particles into polyhedra. In this study, we determined the amino acid sequence of VP3 required for occlusion of viral particles into polyhedra and proposed that this sequence could be used as an immobilization signal to direct the stable incorporation of foreign proteins into polyhedra. A large-scale survey revealed that the immobilization signal could, in fact, direct the incorporation of a variety of human proteins into polyhedra. Immune reactivity and protein-protein interactions were detected on the surface of polyhedra containing immobilized foreign proteins, and these particles were shown to be highly stabilized against dehydration. We showed that these particles could be arrayed onto a glass slide by standard spotting and laser manipulation methods. Thus, this approach is well suited for protein expression, purification, and the development of protein microarrays.

Characterization of the RNA-binding domain in the Dendrolimus punctatus cytoplasmic polyhedrosis virus nonstructural protein p44

Dendrolimus punctatus cytoplasmic polyhedrosis virus (DpCPV-1) belongs to the Cypovirus genus in the Reoviridae family. The ORF of genome segment 8 (S8) of DpCPV-1 was cloned into vector pMAL-c2X and used to express a 44kDa protein (p44) in E. coli, which was detected by Western blotting. The gel mobility shift assays showed that p44 had ssRNA-binding activity. Competitive assay indicated that this protein only bind to ssRNA and could not interact with DNA and dsRNA. The binding of p44 to ssRNA is sequence non-specific. To identify the domain(s) important for RNA binding of the protein, a number of deletions were made. These truncated proteins were expressed in E. coli and purified. The affinity of each truncated protein towards ssRNA was then assayed by electrophoretic mobility shift assays and northwestern blot. The results indicated that glutamic acid-rich domain in the central region of p44 from residues 104 to 201 was the ssRNA-binding domain.

Commensal and mutualistic relationships of reoviruses with their parasitoid wasp hosts

During evolution, certain endoparasitoid wasps have developed mechanisms to suppress the defence systems of their hosts. For this purpose, these species, all of which belong to the families Ichneumonidae and Braconidae, inject various kinds of virus-like particles. The most studied of these particles are classified as polydnaviruses (family Polydnaviridae) which are symbiotic viruses. Over the past decade, it has also been shown that several wasp species harbour reoviruses (family Reoviridae), and that two of these suppress host defence, allowing the development of the parasitoid eggs. In this paper, we summarize the key features of these viruses and their relationships with their wasp hosts. Five reoviruses are known that appear to be non-pathogenic for the wasps. Three of these, McRVLP, HeRV, OpRVLP, use their wasp hosts as vectors, and do not appear to be involved in host defence suppression. The fourth, DpRV-1, is a commensal reovirus detected in most field populations of the wasp, Diadromus pulchellus. This reovirus is always found associated with an ascovirus, DpAV-4a, which is indispensable for host immune suppression. Although DpRV-1 has not been shown to directly increase D. pulchellus parasitic success, it may contribute to this success by retarding DpAV-4a replication in the wasp. The fifth reovirus, DpRV-2, occurs in a specific population of D. pulchellus in which DpRV-1 and DpAV-4 are absent. This virus has a mutualistic relationship with its wasp host, as its injection by females during oviposition is essential for host immunosuppression. Interestingly, these viruses belong to several different reovirus genera.

Complete genome sequence of Mycoreovirus-1/Cp9B21, a member of a novel genus within the family Reoviridae, isolated from the chestnut blight fungus Cryphonectria parasitica

Mycoreovirus 1 (MYRV-1) is the type species of the newly described genus Mycoreovirus of the large virus family Reoviridae. The virus was isolated from a hypovirulent strain (9B21) of the chestnut blight fungus, Cryphonectria parasitica. A previous study showed that double-shelled particles introduced to fungal spheroplasts resulted in stably infected colonies. Of the 11 double-stranded RNA genomic segments (S1-S11), the three largest (S1-S3) were sequenced previously and shown to have moderate levels of similarity to the homologous segments of mammal-pathogenic coltiviruses (Eyach virus and Colorado tick fever virus) and another fungus-infecting reovirus, Mycoreovirus 3 of Rosellinia necatrix strain W370 (MYRV-3/RnW370). The sequences of the remaining segments (S4-S11) are reported here. All of the segments have single ORFs on their positive strands and the terminal sequences 5'-GAUCA----GCAGUCA-3' are conserved among currently and previously sequenced segments. Oligo-cap analysis showed that the positive strands of the genomic segments are capped, whereas the negative strands are not. Similarities among the four evolutionarily related viruses include low or moderate levels of amino acid sequence identity (14.7-34.2 %) and isoelectric points among equivalent polypeptides, e.g. proteins encoded by segments S4 and S5 of the four viruses. Phylogenetic analysis indicated that MYRV-1/Cp9B21 is related more closely to MYRV-3/RnW370 than to the coltiviruses. An interesting dissimilarity is found in codon-choice pattern among the four viruses, i.e. MYRV-1/Cp9B21 segments have a lower frequency of [XYG+XYC] than corresponding segments of the other viruses, suggesting a possible adjustment of virus codon usage to their host environments.

The cypovirus Diadromus pulchellus RV-2 is sporadically associated with the endoparasitoid wasp D. pulchellus and modulates the defence mechanisms of pupae of the parasitized leek-moth, Acrolepiopsis assectella

Diadromus pulchellus is a solitary endoparasitoid wasp that parasitizes the pupae of the leek-moth, Acrolepiosis assectella (Lepidoptera). Hitherto, every individual D. pulchellus from France that has been investigated was infected by an orthoreovirus, DpRV-1, and an ascovirus, DpAV-4. Recently, a new strain of D. pulchellus, established from a French field population, was found to be able to develop on leek-moth pupae, but lacked both DpRV-1 and DpAV-4. However, all these wasps were infected with a new cypovirus, DpRV-2. This cypovirus is transmitted to the A. assectella pupae at each wasp oviposition and is replicated mainly in the gut cells of the parasitized pupae. DpRV-2, like the ascovirus DpAV-4, is able to inhibit the defence reaction of A. assectella pupae and so contributes to the parasitic success of D. pulchellus wasps.

Molecular analysis of Fiji disease Fijivirus genome segments 1 and 3

Fiji disease fijivirus (FDV) genomic segments 1 (S1) and 3 (S3) were completely sequenced. FDV S1 comprised 4,532 nt and was predicted to encode a 170.6 kDa protein. FDV S3 comprised 3,623 nt and was predicted to encode a 135.5 kDa protein. The terminal sequences of S1 and S3 were 5' AAGUUUUU......CAGCUAGCGUC 3' and 5' AAGUUUUU......CAGCAGAUGUC 3', respectively, and located immediately adjacent to these sequences were 12 bp imperfect inverted repeats. The predicted translation product of FDV S1 showed highest similarity to Rice black-streaked dwarf virus (RBSDV) S1 and is thought to encode the viral RNA-dependent RNA polymerase (RdRp). The predicted translation product of FDV S3 was found to be most similar to RBSDV S4 which is thought to encode the 'B-spike' protein. The FDV sequence contained an ATP/GTP binding motif and a leucine zipper motif, but these motifs were not found in the RBSDV sequence. Phylogenetic analysis based on the amino acid sequences of the RdRp of FDV S1 and other reoviruses revealed that the fijiviruses form a cluster close to the oryzaviruses. The RdRp sequences were grouped into genera that were consistent with the current reovirus classification scheme that is based on physico-chemical and biological properties.

Structural comparisons of empty and full cytoplasmic polyhedrosis virus. Protein-RNA interactions and implications for endogenous RNA transcription mechanism

Viruses in the family Reoviridae are capable of transcription within the intact capsids. As the only single-shelled and thus the simplest member of the Reoviridae, cytoplasmic polyhedrosis virus (CPV) provides an attractive system for studying endogenous transcription. We report the structures of the full and empty CPV determined at 13-A resolution by electron cryomicroscopy. The structure of the empty CPV reveals a density attributed to the transcription enzyme complex, which is attached to the internal surface of the capsid shell below each of the 12 turrets. The full capsid has an identical capsid shell but contains additional internal densities contributed by the genomic double-stranded (ds) RNA. The RNA densities proximal to the capsid shell are organized into layers with a dodecahedral appearance, suggesting a genome organization of dsRNA segments each having a cone shape spooling around a transcription enzyme complex. Our structures also suggest that the capsid shell serves as a scaffold for appropriate positioning of the RNA genome, whereas nascent mRNA release takes place through the constricted central channel of the turret. Based on these observations, a detailed moving template transcription mechanism is proposed that may provide insight into the well coordinated and highly efficient endogenous RNA transcription of dsRNA viruses.

Molecular interactions and viral stability revealed by structural analyses of chemically treated cypovirus capsids

Cytoplasmic polyhedrosis virus (CPV, genus Cypovirus) is a unique member of the family Reoviridae which lacks the outer protective shells that exist in all other members, yet exhibits unusual stability. We have analyzed the effects of different acidic, basic, detergent, and urea treatments on CPV capsids. The integrity of the CPV capsids was unaffected under high-pH conditions that disrupted the orthoreovirus inner core, consistent with its ability to maintain structural integrity in extremely alkaline environments during infection. However, it was sensitive to low pH, detergents, and urea, similarly to other viruses in this family. The three-dimensional structure comparisons by electron cryomicroscopy of the intact empty CPV capsid with the "spikeless" capsid whose turrets were removed by chemical treatments revealed the interaction footprint of the turret on the capsid shell. The observed structural changes associated with the removal of the turret suggest critical structural roles of the turret in maintaining capsid integrity in addition to its enzymatic activities.

Molecular cloning and characterization of Antheraea mylitta cytoplasmic polyhedrosis virus genome segment 9

Genome segment 9 of the 11-segment RNA genomes of three cytoplasmic polyhedrosis virus (CPV) isolates from Antheraea mylitta (AmCPV), Antheraea assamensis (AaCPV) and Antheraea proylei (ApCPV) were converted to cDNA, cloned and sequenced. In each case, this genome segment consists of 1473 nucleotides with one long ORF of 1035 bp and encodes a protein of 345 amino acids, termed NSP38, with a molecular mass of 38 kDa. Secondary structure prediction showed the presence of nine alpha-helices in the central and terminal domains with localized similarity to RNA-binding motifs of bluetongue virus and infectious bursal disease virus RNA polymerases. Nucleotide sequences were 99.6% identical between these three strains of CPVs, but no similarity was found to any other nucleotide or protein sequence in public databases. The ORF from AmCPV cDNA was expressed as a His-tagged fusion protein in E. coli and polyclonal antibody was raised against the purified protein. Immunoblot as well as immunofluorescence analysis with anti-NSP38 antibody showed that the protein was not present in polyhedra or uninfected cells but was present in AmCPV-infected host midgut cells. NSP38 was expressed in insect cells as soluble protein via a baculovirus expression vector and shown to possess the ability to bind poly(rI)-(rC) agarose, which was competitively removed by AmCPV viral RNA. These results indicate that NSP38 is expressed in virus-infected cells as a non-structural protein. By binding to viral RNA, it may play a role in the regulation of genomic RNA function and packaging.

Nucleotide sequences of segments 1, 3 and 4 of the genome of Bombyx mori cypovirus 1 encoding putative capsid proteins VP1, VP3 and VP4, respectively

The complete nucleotide sequences of genomic segments S1, S3 and S4 from Bombyx mori cypovirus 1 (BmCPV-1) have been determined. The segments consisted of 4190, 3846 and 3262 nucleotides encoding putative proteins of 1333, 1239 and 1058 amino acids with molecular masses of approximately 148, 140 and 120 kDa (p148, p140 and p120, respectively). All segments possess a single open reading frame. Homology searches showed that all three proteins have homologies to proteins of Rice ragged stunt virus, a member of the genus Oryzavirus within the family REOVIRIDAE: Partial homologies of p140 to structural proteins in other viruses were also found. The predicted molecular masses and the homologies with structural proteins in other viruses lead us to suggest that S1, S3 and S4 encode the capsid proteins VP1, VP3, and VP4, respectively, of BmCPV-1.