Molecular characterization of segments 7-10 of Dendrolimus punctatus cytoplasmic polyhedrosis virus provides the complete genome

Heat shock protein 70, glutamate dehydrogenase, and angiotensin-converting enzyme of Bombyx mori mediate the cell attachment of Cypovirus 1

Dendrolimus punctatus causes great damage to pine forests worldwide. Dendrolimus punctatus cypovirus 1 (DpCPV-1) is an important pathogen of D. punctatus. However, the mechanism of DpCPV-1 cell entry has not been elucidated. In this study, we revealed that both GTase and MTase domains of VP3 (B-spike) and VP4 (A-spike) of DpCPV-1 interacted with the midgut proteins of Bombyx mori. Binding and competition assays revealed that GTase, MTase and VP4 played roles as viral attachment proteins. Far-Western blotting and LC-MS/MS analyses identified that heat shock protein 70 (BmHSP70), glutamate dehydrogenase (BmGDH), and angiotensin-converting enzyme (BmACE) in the midgut proteins as ligand candidates of the viral attachment proteins, and this was further verified by co-immunoprecipitation and fluorescence co-localization assays. Viral binding to the host midgut in vitro was inhibited by pre-treating B. mori midgut proteins with anti-BmHSP70, anti-BmGDH, anti-BmACE antibodies singly and in combination. Incubating DpCPV-1 virions with prokaryotically expressed BmHSP70, BmGDH, and BmACE also decreased viral attachment to the host midgut. In vivo bioassays revealed that viral infection in Helicoverpa armigera was partially neutralized by BmHSP70, BmGDH, and BmACE. Taking together, we concluded that HSP70, GDH, and ACE mediate DpCPV attachment and entry via binding to the viral attachment proteins, VP3 and VP4. The findings provide foundation for further understanding the entry mechanisms of cypoviruses.

Identification and characterization of vp7 gene in Bombyx mori cytoplasmic polyhedrosis virus

The genome of Bombyx mori cytoplasmic polyhedrosis virus (BmCPV) contains 10 double stranded RNA segments (S1-S10). The segment 7 (S7) encodes 50kDa protein which is considered as a structural protein. The expression pattern and function of p50 in the virus life cycle are still unclear. In this study, the viral structural protein 7 (VP7) polyclonal antibody was prepared with immunized mouse to explore the presence of small VP7 gene-encoded proteins in Bombyx mori cytoplasmic polyhedrosis virus. The expression pattern of vp7 gene was investigated by its overexpression in BmN cells. In addition to VP7, supplementary band was identified with western blotting technique. The virion, BmCPV infected cells and midguts were also examined using western blotting technique. 4, 2 and 5 bands were detected in the corresponding samples, respectively. The replication of BmCPV genome in the cultured cells and midgut of silkworm was decreased by reducing the expression level of vp7 gene using RNA interference. In immunoprecipitation experiments, using a polyclonal antiserum directed against the VP7, one additional shorter band in BmCPV infected midguts was detected, and then the band was analyzed with mass spectrum (MS), the MS results showed thatone candidate interacted protein (VP7 voltage-dependent anion-selective channel-like isoform, VDAC) was identified from silkworm. We concluded that the novel viral product was generated with a leaky scanning mechanism and the VDAC may be an interacted protein with VP7.

Genomic and biological characterization of a new cypovirus isolated from Dendrolimus punctatus

A novel cypovirus (designated DpCPV-MC) was isolated from the pine moth Dendrolimus punctatus using serial in vivo cloning procedures. DpCPV-MC occurs in typical polyhedral occlusion bodies, containing a number of spherical virions. Laboratory bioassays indicated that the infectivity of DpCPV-MC against second-instar Spodoptera exigua larvae does not differ significantly from that of Dendrolimus punctatus cypovirus 1. Full-length amplification of the DpCPV-MC cDNAs identified 16 dsRNA genome segments. Each segment encodes one open reading frame with unique conserved terminal sequences at the 5′ and 3′ ends, which differ from those of all previously reported cypoviruses. On a phylogenetic tree based on the amino acid sequences of the polyhedrin of 19 cypovirus species, DpCPV-MC was closest to the type-4 cypoviruses. Homology searches showed that ten segments of DpCPV-MC (S1, S2, S3, S4, S5, S7, S8, S9, S12, and S13) encode putative CPV structural and nonstructural proteins, three segments (S6, S10 and S14) encode putative insect proteins or other viral proteins, and the other three segments (S11, S15, and S16) encode proteins that have no obvious sequence similarity to any known protein. Based on RNA secondary structures analysis, two segments of them (S11 and S16) were predicted to possibly transcript less efficiently than the other segments. We speculate that DpCPV-MC is composed of several genotypes. The ten CPV-related segments constantly exist in all genotypes, and one or two of the six CPV-unrelated segments co-exist with the ten CPV-related segments in one DpCPV-MC genotype, thus each virion contains no more than 12 segments. Based on our results and the literature, DpCPV-MC is a new cypovirus (Cypovirus 22, strain DpCPV-22).

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.

Molecular characterization of protein p50 of Dendrolimus punctatus cytoplasmic polyhedrosis virus

Genome segment 7 of the 10-segmented RNA genomes of Dendrolimus punctatus cytoplasmic polyhedrosis virus (DpCPV) comprises 1502 nucleotides with one ORF of 1347 bp. This ORF was predicted to encode a protein of 448 amino acids with a molecular mass of 49,756 Da (p50). Antisera against both p50 and an antigen domain (AD) near the N-terminus of p50 specifically bound to a viral structural protein of ca. 33 kDa (V5), indicating that V5 was an N-terminal product of p50. Immunoblotting analysis with anti-p50 antibodies detected p50 and V5 molecules in the host midguts three days and five days post infection, respectively. The intracellular localization of p50 protein was examined by expressing truncations of p50 fused with GFP in recombinant baculovirus-infected Sf9 cells. The p50 protein was present in the cytoplasm of the cells, and the N-terminal portion (67-135 aa) of the protein played a key role in this localization.

Molecular characterization of genome segments 1 and 3 encoding two capsid proteins of Antheraea mylitta cytoplasmic polyhedrosis virus

Background

Antheraea mylitta cytoplasmic polyhedrosis virus (AmCPV), a cypovirus of Reoviridae family, infects Indian non-mulberry silkworm, Antheraea mylitta, and contains 11 segmented double stranded RNA (S1-S11) in its genome. Some of its genome segments (S2 and S6-S11) have been previously characterized but genome segments encoding viral capsid have not been characterized.

Results

In this study genome segments 1 (S1) and 3 (S3) of AmCPV were converted to cDNA, cloned and sequenced. S1 consisted of 3852 nucleotides, with one long ORF of 3735 nucleotides and could encode a protein of 1245 amino acids with molecular mass of ~141 kDa. Similarly, S3 consisted of 3784 nucleotides having a long ORF of 3630 nucleotides and could encode a protein of 1210 amino acids with molecular mass of ~137 kDa. BLAST analysis showed 20-22% homology of S1 and S3 sequence with spike and capsid proteins, respectively, of other closely related cypoviruses like Bombyx mori CPV (BmCPV), Lymantria dispar CPV (LdCPV), and Dendrolimus punctatus CPV (DpCPV). The ORFs of S1 and S3 were expressed as 141 kDa and 137 kDa insoluble His-tagged fusion proteins, respectively, in Escherichia coli M15 cells via pQE-30 vector, purified through Ni-NTA chromatography and polyclonal antibodies were raised. Immunoblot analysis of purified polyhedra, virion particles and virus infected mid-gut cells with the raised anti-p137 and anti-p141 antibodies showed specific immunoreactive bands and suggest that S1 and S3 may code for viral structural proteins. Expression of S1 and S3 ORFs in insect cells via baculovirus recombinants showed to produce viral like particles (VLPs) by transmission electron microscopy. Immunogold staining showed that S3 encoded proteins self assembled to form viral outer capsid and VLPs maintained their stability at different pH in presence of S1 encoded protein.

Conclusion

Our results of cloning, sequencing and functional analysis of AmCPV S1 and S3 indicate that S3 encoded viral structural proteins can self assemble to form viral outer capsid and S1 encoded protein remains associated with it as inner capsid to maintain the stability. Further studies will help to understand the molecular mechanism of capsid formation during cypovirus replication.

Genome segment 6 of Antheraea mylitta cypovirus encodes a structural protein with ATPase activity

The genome segment 6 (S6) of the 11 double stranded RNA genomes from Antheraea mylitta cypovirus was converted into cDNA, cloned and sequenced. S6 consisted of 1944 nucleotides with an ORF of 607 amino acids and could encode a protein of 68 kDa, termed P68. Motif scan and molecular docking analysis of P68 showed the presence of two cystathionine beta synthase (CBS) domains and ATP binding sites. The ORF of AmCPV S6 was expressed in E. coli as His-tag fusion protein and polyclonal antibody was raised. Immunoblot analysis of virus infected gut cells and purified polyhedra using raised anti-p68 polyclonal antibody showed that S6 encodes a viral structural protein. Fluorescence and ATPase assay of soluble P68 produced in Sf-9 cells via baculovirus expression system showed its ability to bind and cleave ATP. These results suggest that P68 may bind viral RNA through CBS domains and help in replication and transcription through ATP binding and hydrolysis.

Characterisation and partial sequence analysis of two novel cypoviruses isolated from the winter moth Operophtera brumata (Lepidoptera: Geometridae)

The complete nucleotide sequences of genomic segments S5 to S10 from Operophtera brumata cypovirus 18 (OpbuCPV18), and the complete nucleotide sequences of genomic segments S2, S5, S9 and S10 from Operophtera brumata cypovirus 19 (OpbuCPV19) have been determined. Each genome segment contained a single open reading frame (ORF). Conserved motifs 5' (AGUAAA....GUUAGCU) 3' were found at the ends of each segment of OpbuCPV18, whilst conserved motifs 5' (AACAAA....UUUGC) 3' were found at each segment terminus of OpbuCPV19. The putative proteins were compared with those of other members of the Reoviridae family. Phylogenetic analysis using the polyhedrin gene (S10) indicated that OpbuCPV18 was most closely related to Dendrolimus punctatus cypovirus 1, whilst OpbuCPV19 was most closely related to Trichoplusia ni cypovirus 15. In addition, analysis of S2, which encoded a putative RNA-dependant RNA polymerase gene, confirmed OpbuCPV19 belonged to the genus Cypovirus. Following the expression of the ORF from OpbuCPV19 S10, using a baculovirus expression vector, occlusion bodies were observed in insect cell culture. This demonstrated that segment 10 coded for the polyhedrin gene, capable of forming a polyhedral crystalline matrix.

Molecular cloning, sequence analysis and expression of genome segment 7 (S7) of Antheraea mylitta cypovirus (AmCPV) that encodes a viral structural protein

The Genome segment 7 (S7) of the 11 double stranded RNA genomes from Antheraea mylitta cypovirus (AmCPV) was converted to cDNA, cloned and sequenced. The nucleotide sequence showed that segment 7 consisted of 1789 nucleotides with an ORF of 530 amino acids and could encode a protein of approximately 61 kDa, termed P61. The 5' terminal sequence, AGTAAT and the 3' terminal sequence, AGAGC of the plus strand was found to be the same as genome segment 10 of AmCPV encoding polyhedrin. No sequence similarity was found by searching nucleic acid and protein sequence databases using BLAST. The secondary structure prediction showed the presence of 17 alpha-helices, 18 extended beta-sheets along the entire length of P61. The ORF of segment 7 was expressed in E. coli as His-tagged fusion protein, purified through Ni-NTA chromatography, and polyclonal antibody was raised in rabbit indicating that P61 is immunogenic. Immunoblot analysis using this antibody on viral infected cells as well as purified polyhedra showed that P61 is a viral structural protein. Motif scan search showed some similarity of P61 with Inosine monophosphate dehydrogenase (IMPDH) cystathionine-beta-synthase (CBS) domain at the C-terminus and it was hypothesized that by binding to single stranded viral RNA through its CBS domain P61 may help in virus replication or transcription.

Identification of Transmembrane Domain of a Membrane Associated Protein NS5 of Dendrolimus punctatus Cytoplasmic Polyhedrosis Virus

We examined the intracellular localization of NS5 protein of Dendrolimus punctatus cytoplasmic polyhedrosis virus (DpCPV) by expressing NS5-GFP fusion protein and proteins from deletion mutants of NS5 in baculovirus recombinant infected insect Spodoptera frugiperda (Sf-9) cells. It was found that the NS5 protein was present at the plasma membrane of the cells, and that the N-terminal portion of the protein played a key role in the localization. A transmembrane region was identified to be present in the N-terminal portion of the protein, and the detailed transmembrane domain (SQIHMVWVKSGLVFF, 57-71aa) of N-terminal portion of NS5 was further determined, which was accorded with the predicted results, these findings suggested that NS5 might have an important function in viral life cycle.

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.

Mapping the RNA-binding domain on the DpCPV VP4

The RNA-binding properties of VP4 protein of Dendrolimus punctatus cytoplasmic polyhedrosis virus (DpCPV) VP4 were analyzed. VP4 was expressed in E. coli and assayed for RNA binding activity by gel mobility shift assay. VP4 was found to bind RNA (ssRNA and dsRNA) in a sequence-independent manner, but did not interact with DNA. To identify the domain(s) of the protein important for RNA binding, a number of deletions were made and tested by gel mobility shift assays and northwestern blot. The central region of VP4 from amino acid residues 77 to 155 was found to contain the RNA binding domain.

Molecular cloning and characterization of Antheraea mylitta cytoplasmic polyhedrosis virus polyhedrin gene and its variant forms

The segments 10 (S10) of the 11 double stranded RNA genomes from Antheraea mylitta cytoplasmic polyhedrosis virus (AmCPV) encoding a novel polyhedrin polypeptide was converted to cDNA, cloned, and sequenced. Three cDNA clones consisting of 1502 (AmCPV10-1), 1120 (AmCPV10-2), and 1415 (AmCPV10-3) nucleotides encoding polyhedrin of 254, 339, and 319 amino acids with molecular masses of 29, 39, and 37 kDa, respectively, were obtained, and verified by Northern analysis. These clones showed 70-94% sequence identity among them but none with any sequences in databases. The expression of AmCPV10-1 cDNA encoded polyhedrin in Sf-9 cells was detected by immunoblot analysis and formation of polyhedra by electron microscopy, as observed in AmCPV-infected gut cells, but no expression of AmCPV10-2 or AmCPV10-3 cDNA was detected, indicating that during AmCPV replication, along with functional S10 RNA, some defective variant forms of S10 RNAs are packaged in virion particles.

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.