Genetic modification of an entomopoxvirus: deletion of the spheroidin gene does not affect virus replication in vitro

The protein-protein interactions between Amsacta moorei entomopoxvirus (AMEV) protein kinases (PKs) and all viral proteins

Entomopoxviruses are an important group of viruses infecting only insects. They belong to Poxviridae which infect both invertebrates and vertebrates, including humans. Protein kinases are known to have roles at virus morphogenesis, host selectivity, the regulation of cell division and apoptosis in some vertebrate poxviruses. In this study, 2 protein kinases (PKs) (AMV153 and AMV197) of Amsacta moorei entomopoxvirus (AMEV) were investigated for the interactions among 230 viral proteins using yeast two-hybrid system (Y2H). For this purpose, two protein kinases and 230 viral genes were cloned into the bait and prey vectors, respectively. Bait vectors were introduced into Saccharomyces cerevisiae AH109. Expression of the bait genes were confirmed by western blot analysis. Both yeast strains of bait were transformed individually with each prey clone and grown on a selective medium (minimal synthetic defined) to determine the protein-protein interactions between bait and prey proteins. Transformations identified totally 16 interactions among AMEV protein kinases and all viral proteins of which 5 belong to AMV153 and 11 belong to AMV197. One of the five interactions detected for AMV153 protein kinase is self-association. Its other four interactions are with two virus entry complex proteins (AMV035 and AMV083), a membrane protein (AMV165) and a subunit of RNA polymerase (AMV230). The other protein kinase, AMV197, interacted with two virus entry complex proteins (AMV035 and AMV083) as AMV153, a caspase-2 enzyme (AMV063), a Holliday junction resolvase (AMV162), a membrane protein (AMV165), a subunit of RNA polymerase (AMV230) and five other hypothetical proteins (AMV026, AMV040, AMV062, AMV069, AMV120) encoded by AMEV genome. Glutathione S-transferase (GST) pull-down assay was used to confirm all interactions described by Y2H analysis. In addition, the theoretical structures of the two of 16 interactions were interpreted by docking analysis. Consistent with Y2H and pull down assays, docking analysis also showed the interactions of AMV063 with AMV153 and AMV197. Detected interactions of the AMEV viral proteins with viral protein kinases could lead to the understanding of the regulation of the viral activities of interacted viral proteins.

Transcriptional analysis of the putative glycosyltransferase gene (amv248) of the Amsacta moorei entomopoxvirus

Amsacta moorei entomopoxvirus (AMEV), the most studied member of the genus Betaentomopoxvirus, was initially isolated from Red Hairy caterpillar larvae, Amsacta moorei. According to genome sequence and previous studies it was shown that amv248 encodes a putative glycosyltransferase that is the only conserved attachment protein in betaentomopoxviruses. Transcriptional analysis of the amv248 gene by RT-PCR and qPCR showed that transcription starts at 6h post infection (hpi). Also, transcription was not affected by a DNA replication inhibitor but was severely curtailed by a protein synthesis inhibitor. These results indicate that amv248 belongs to the intermediate class of gene expression. 5' and 3' untranslated regions analysis revealed that transcription initiates at position -126 relative to the translational start site, and ends between 50 and 83 bases after the stop codon. To narrow down the size and location of the gene's promoter, the upstream region as well as several different sized deletions thereof were generated and cloned upstream of a luciferase reporter gene. The constructs were used to measure the Firefly and Renilla luciferase activities in dual assays. The results showed that luciferase activity decreased when bases -198 to -235 of amv248 upstream region were missing. Sequence analysis among the intermediate gene promoters of AMEV showed that TTTAT(T/A)TT(T/A)₂TTA is possibly a common motif, however, further investigations are needed to confirm this conclusion.

Fitness-related traits of entomopoxviruses isolated from Adoxophyes honmai (Lepidoptera: Tortricidae) at three localities in Japan

Three entomopoxviruses (EPVs) isolated from diseased Adoxophyes honmai larvae at different localities (Tsukuba, Itsukaichi, and Miyazaki) in Japan were compared for biochemical identity and key parameters of virus fitness, fatal infection, speed of kill, and virus yield. When the structural peptides of occlusion bodies (OBs) and occlusion-derived viral particles were compared using sodium dodecyl sulfate-polyacrylamide gel electrophoresis, no difference in banding patterns was observed. However, DNA restriction endonuclease analysis showed that the three isolates were genotypically different, but many commonly sized DNA fragments were observed. Five tortricid species, A. honmai, Adoxophyes orana, Adoxophyesdubia, Homona magnanima, and Archips insulanus were susceptible to all isolates. No significant differences in the key viral fitness parameters were detected among the isolates in A. orana. However, the Miyazaki isolate had a different effect on H. magnanima; it allowed infected insects to survive longer and develop to a larger size, but had a lower yield of OBs per larva at any given time to death. OB yields per unit cadaver weight for the Miyazaki isolate, which indicate the conversion rate of the insect to virus, were lower over time compared to the other two isolates. The implications for selecting a candidate isolate to control tortricid pests are discussed.

Assessment of foreign protein production by recombinant Heliothis (Helicoverpa) armigera entomopoxviruses in Spodoptera frugiperda cells

This report describes the first production of recombinant forms of Heliothis (Helicoverpa) armigera entomopoxvirus (HaEPV). These HaEPVs are engineered at either the spheroidin or fusolin locus, to produce the green fluorescent marker protein (GFP). The growth properties of these recombinant HaEPVs, in comparison to the parental HaEPV, were assessed in cultured Spodoptera frugiperda Sf9 cells. Additionally, GFP production by these recombinant HaEPVs was compared to that of a GFP-expressing recombinant of the baculovirus Autographa californica nucleopolyhedrovirus (AcNPV) in the same in vitro system, at various multiplicities of infection. Expression of GFP from the HaEPV spheroidin locus produced up to 60% of that generated from the AcNPV polyhedrin locus, albeit over a longer period of infection. A considerably lower yield was recorded from the HaEPV fusolin locus, a result that contrasted markedly with the apparent activity of this promoter in caterpillar infections in vivo. The potential applications for further development of HaEPV expression systems are discussed.

Complete genomic sequence of the Amsacta moorei entomopoxvirus: analysis and comparison with other poxviruses

The genome of the genus B entomopoxvirus from Amsacta moorei (AmEPV) was sequenced and found to contain 232,392 bases with 279 unique open reading frames (ORFs) of greater than 60 amino acids. The central core of the viral chromosome is flanked by 9.4-kb inverted terminal repeats (ITRs), each of which contains 13 ORFs, raising the total number of ORFs within the viral chromosome to 292. ORFs with no known homology to other poxvirus genes were shown to constitute 33.6% of the viral genome. Approximately 28.6% of the AmEPV genome encodes homologs of the mammalian poxvirus colinear core genes, which are found dispersed throughout the AmEPV chromosome. There is also no significant gene order conservation between AmEPV and the orthopteran genus B poxvirus of Melanoplus sanguinipes (MsEPV). Novel AmEPV genes include those encoding a putative ABC transporter and a Kunitz-motif protease inhibitor. The most unusual feature of the AmEPV genome relates to the viral encoded poly(A) polymerase. In all other poxviruses this heterodimeric enzyme consists of a single large and a single small subunit. However, AmEPV appears to encode one large and two distinct small poly(A) polymerase subunits. AmEPV is one of the few entomopoxviruses which can be grown and manipulated in cell culture. The complete genomic sequence of AmEPV paves the way for an understanding and comparison of the molecular properties and pathogenesis between the entomopoxviruses of insects and the more intensively studied vertebrate poxviruses.

The spheroidin of an entomopoxvirus isolated from the grasshopper Anacridium aegyptium (AaEPV) shares low homology with spheroidins from lepidopteran or coleopteran EPVs

Based on virion morphology, the current virus taxonomy groups entomopoxviruses (EPVs) (Poxvirus: Entomopoxvirinae) from coleopteran and dipteran hosts in separated genera, wilts it keeps viruses infecting either lepidopteran or orthopteran hosts in the same genus. In contrast to the morphological criteria, the few data available from recent studies at the genetic level have suggested that EPVs infecting different insect orders are phylogenetically distant. In order to elucidate EPVs phylogeny we have cloned and sequence the highly conserved/highly expressed spheroidin gene of Anacridium aegyptium entomopoxvirus (AaEPV). This gene and its promoter is of interest for the development of genetic engineering on EPVs. The spheroidin gene was located in the AaEPV genome by Southern blot and hybridisation with specific degenerated oligonucleotides probes synthesised after partial sequencing of the purified spheroidin protein. A total of 3489 bp were sequenced. This sequence included the coding and promoter region of 969 residues 108. 8 kDa protein identified as spheroidin. AaEPV spheroidin contains 21 cysteine residues (2.2%) and 14 N-glycosylation putative sites distributed along the sequence. The cysteine residues are particularly abundant at the C-terminal end of the protein, with 11 residues in the last 118 aa. Our results confirm that the spheroidin is highly conserved only between EPVs isolated from the same insect order. Polyclonal antibodies raised against AaEPV spherules specifically revealed spheroidin in Western Blots failing to cross-react with MmEPV or AmEPV spheroidins or MmEPV fusolin. Comparison of spheroidins at the aa level demonstrate that AaEPV spheroidin shares only 22.2 and 21.9% identity with the lepidopteran AmEPV and the coleopteran MmEPV spheroidins, respectively, but 82.8% identity with the orthopteran MsEPV spheroidin. Only two highly conserved domains containing the sequence (V/Y)NADTG(C/L) and LFAR(I/A) have been identified in all known spheroidins. The phylogenetic tree constructed according to the CLUSTALX analysis program revealed that EPVs are clearly separated in three groups - lepidopteran, coleopteran and orthopteran - according to the insect order of the virus hosts. In base to our results, the split of the genus Entomopoxvirus B dissociating lepidopteran and orthopteran EPVs into two different genera is suggested.

Complete nucleotide sequence of spheroidin gene of Anomala cuprea entomopoxvirus

The complete nucleotide sequence of the spheroidin gene of Anomala cuprea entomopoxvirus (AcEPV) was determined. The sequence was compared with those of spheroidin genes of EPVs such as Melolontha melolontha EPV (MmEPV, Genus A), Choristoneura fumiferana EPV (CfEPV, Genus B) and Amsacta moorei EPV (AmEPV, Genus B). The gene harbored an open reading frame (ORF) of 2826 nt, with the same size as that of MmEPV belonging to the same genus, capable of coding for a polypeptide of 109.0 kDa. The predicted amino acid (aa) sequence showed a greater or moderate similarity to the corresponding sequence of the other EPVs, showing a 94, 40 and 41% aa identity with MmEPV, CfEPV and AmEPV, respectively; the identity was 89, 53 and 54% at the nucleotide level. The hydropathy plots also showed a greater similarity in organization to MmEPV and moderate similarity to the viruses of Genus B. In the polypeptide, 44 cysteine residues, which are likely to be involved in paracrystal formation and seven potential N-glycosylation sites were detected. The number of cysteine residues and N-glycosylation sites also depended on the difference in genera (A or B). Thus, the spheroidin gene of EPVs was well conserved within the same genus.

Cloning, sequencing and transcriptional analysis of the Choristoneura fumiferana entomopoxvirus spheroidin gene

The Choristoneura fumiferana entomopoxvirus (CfEPV) spheroidin gene was identified and localized on three XbaI restriction fragments (total size 4.73 kb). The fragments were cloned and sequenced. The spheroidin gene had an open reading frame of 2997 nucleotides encoding a putative protein with a predicted size of 115 kDa. Sequence analysis indicated that the putative protein contained 14 potential N-glycosylation sites (Asn-X-Thr; Asn-X-Ser), that are probably not used since the protein migrates on SDS-PAGE as a 115 kDa band. The protein is rich in cysteine residues (34), which explains the need for reducing agents when dissolving the occlusion bodies with alkali. The spheroidin gene sequence contains motifs characteristic of the late genes of poxviruses. These include the typical TAAATG sequence at the beginning of the coding region and two early gene termination signals (TTTTTNT) in the untranslated region of the gene. The promoter region has three TAA termination signals immediately upstream of the ATG start site. Spheroidin (SPH) appears to be conserved among different EPVs. There was 82.2% identity and 97.2% similarity at the amino acid level between the SPHs of CfEPV and Amsacta moorei EPV. Less conservation was seen with the SPH from Melolontha melolontha EPV (39.8% identity and 73.4% similarity). Transcriptional analyses of the spheroidin gene by Northern blots showed that the transcript had a size of approximately 3 kb, which is in agreement with the length of the ORF. Primer extension results, anchor PCR and sequencing confirmed that there was a poly (A)17 tract at the 5' end of the spheroidin gene transcript, a structure typical of late gene transcripts of poxviruses.

Identification and characterization of a filament-associated protein encoded by Amsacta moorei entomopoxvirus

A novel protein which is expressed at high levels in insect cells infected with Amsacta moorei entomopoxvirus was identified by our laboratory. This viral gene product migrates as a 25/27-kDa doublet when subjected to electrophoresis on sodium dodecyl sulfate-polyacrylamide gels. It is expressed at late times of infection and is present in infected cells but is absent in purified extracellular virions and occlusion bodies. The gene encoding this polypeptide was mapped on the viral genome, and cDNA clones were generated and sequenced. The predicted protein was shown to be phosphorylated and contained an unusual 10-unit proline-glutamic acid repeat element. A polyclonal antiserum was produced against a recombinant form of the protein expressed in Escherichia coli, and a monoclonal antibody which reacted with the proline-glutamic acid motif was also identified. Immunofluorescence and immunoelectron microscopy techniques revealed that this protein is associated with large cytoplasmic fibrils which accumulate in the cytoplasm between 96 and 120 h postinfection. We subsequently called this viral polypeptide filament-associated late protein of entomopoxvirus. The fibrils containing this polypeptide are closely associated with occlusion bodies and may play a role in their morphogenesis and maturation.