Characterization of a new Autographa californica multiple nucleopolyhedrovirus (AcMNPV) polyhedra mutant

Comparison between different conditions for the incorporation of foreign proteins into Autographa californica multiple polyhedrovirus polyhedra for biotechnological purposes

The occlusion bodies of Autographa californica multiple nucleopolyhedrovirus are proteinaceous formations with significant biotechnological potential owing to their capacity to integrate foreign proteins through fusion with polyhedrin, their primary component. However, the strategy for successful heterologous protein inclusion still requires further refinement. In this study, we conducted a comparative assessment of various conditions to achieve the embedding of recombinant proteins within polyhedra. Two baculoviruses were constructed: AcPHGFP (polh+), with GFP as a fusion to wild type (wt) polyhedrin and AcΔPHGFP (polh+), with GFP fused to a fragment corresponding to amino acids 19 to 110 of polyhedrin. These baculoviruses were evaluated by infecting Sf9 cells and stably transformed Sf9, Sf9POLH, and Sf9POLHE44G cells. The stably transformed cells contributed another copy of wt or a mutant polyhedrin, respectively. Polyhedra of each type were isolated and characterized by classical methods. The fusion PHGFP showed more-efficient incorporation into polyhedra than ΔPHGFP in the three cell lines assayed. However, ΔPHGFP polyhedron yields were higher than those of PHGFP in Sf9 and Sf9POLH cells. Based on an integral analysis of the studied parameters, it can be concluded that, except for the AcΔPHGFP/Sf9POLHE44G combination, deficiencies in one factor can be offset by improved performance by another. The combinations AcPHGFP/Sf9POLHE44G and AcΔPHGFP/Sf9POLH stand out due to their high level of incorporation and the large number of recombinant polyhedra produced, respectively. Consequently, the choice between these approaches becomes dependent on the intended application.

Easily purified baculovirus/insect-system-expressed recombinant hepatitis B virus surface antigen fused to the N- or C-terminus of polyhedrin

Baculoviruses are circular double-stranded DNA viruses that infect insects and are widely used as the baculoviral expression vectors (BEVs), which provide a eukaryotic milieu for heterologous expression. The most frequently used vector is based on Autographa californica multiple nucleopolyhedrovirus (AcMNPV). However, purification of recombinant proteins produced using BEVs is laborious, time-consuming, and often expensive. Numerous strategies have been explored to facilitate purification of heterologous proteins, such as fusion with occlusion body (OBs)-forming proteins like polyhedrin (Polh). Baculoviruses produce OBs in the late stages of infection to protect the virion in the cellular environment, and the main protein responsible for OB formation is Polh. In this study, we investigated the effect of fusing the gene that encodes the surface antigen (S-HBsAg) of hepatitis B virus (HBV) to either the N- or C-terminus of the AcMNPV Polh. The production of recombinant viruses and recombinant proteins was confirmed, and the ability to form chimeric S-HBsAg-containing OBs was accessed by light and scanning electron microscopy of infected cells. The fusion was found to affect the shape and size of the OBs when compared to wild-type OBs, with the N-terminal fusion producing less-amorphous OBs than the C-terminal construct. In addition, the N-terminal construct gave higher levels of expression than the C-terminal construct. Quantitative and qualitative immunoassays with human serum or plasma antibodies against HBsAg showed that the two forms of the antigen reacted differently. Although both reacted with the antibody, the N-terminal fusion protein reacted with more sensitivity (2.27-fold) and is therefore more suitable for quantitative assays than the C-terminal version. In summary, the BEVs represents a promising tool for the production of reagents for the diagnosis of HBV infection.

The autographa californica multiple nucleopolyhedrovirus Ac12: A non-essential F box-like protein that interacts with cellular SKP1 component of the E3 ubiquitin ligase complex

The Autographa californica multiple nucleopolyhedrovirus (AcMNPV) ac12 gene, which is conserved in ten other baculovirus, codes a predicted 217 amino acid protein of unknown function. In this study, we investigated the role of ac12 during baculovirus infection, by generating an ac12 knockout virus. The transfection of the recombinant genome in insect cells resulted in unaltered viral dispersion and occlusion body production when compared to the control bacmid. This finding demonstrates that ac12 is a non-essential gene. Transmission and scanning electron microscopy (SEM) analyses showed that ac12 knockout virus produced occlusion bodies morphologically similar to those obtained with the control and capable to occlude virions. However, a slight but significant size difference was detected by SEM observation of purified occlusion bodies. This difference suggests that ac12 may be involved in regulatory pathways of polyhedrin production or occlusion body assembly without affecting either viral occlusion or oral infectivity in Rachiplusia nu larvae. This was evidenced by bioassays that showed no significant differences in the conditions tested. A qPCR analysis of viral gene expression during infection evidenced regulatory effects of ac12 over some representative genes of different stages of the viral cycle. In this study, we also showed that ac12 is transcribed at early times after infection and remains detectable up to 72 hours post-infection. The mRNA is translated during the infection and results in a protein that encodes an F-box domain that interacts in vivo and in vitro with S phase kinase associated protein 1 (SKP1) adaptor protein, which is potentially involved in protein ubiquitination pathways.

A Novel Betabaculovirus Isolated from the Monocot Pest Mocis latipes (Lepidoptera: Noctuidae) and the Evolution of Multiple-Copy Genes

In this report, we described the genome of a novel baculovirus isolated from the monocot insect pest Mocis latipes, the striped grass looper. The genome has 134,272 bp in length with a G + C content of 38.3%. Based on the concatenated sequence of the 38 baculovirus core genes, we found that the virus is a betabaculovirus closely related to the noctuid-infecting betabaculoviruses including Pseudaletia unipuncta granulovirus (PsunGV), Trichoplusia ni granulovirus (TnGV), Helicoverpa armigera granulovirus (HearGV), and Xestia c-nigrum granulovirus (XecnGV). The virus may constitute a new Betabaculovirus species tentatively named Mocis latipes granulovirus (MolaGV). After gene content analysis, five open reading frames (ORFs) were found to be unique to MolaGV and several auxiliary genes were found including iap-3, iap-5, bro-a, bro-b, and three enhancins. The virus genome lacked both chitinase and cathepsin. We then looked at the evolutionary history of the enhancin gene and found that betabaculovirus acquired this gene from an alphabaculovirus followed by several duplication events. Gene duplication also happened to an endonuclease-like gene. Genomic and gene content analyses revealed both a strict collinearity and gene expansion into the genome of the MolaGV-related species. We also characterized the granulin gene using a recombinant Autographa californica multiple nucleopolyhedrovirus (AcMNPV) and found that occlusion bodies were produced into the nucleus of infected cells and presented a polyhedral shape and no occluded virions within. Overall, betabaculovirus genome sequencing is of importance to the field as few genomes are publicly accessible. Mocislatipes is a secondary pest of maize, rice, and wheat crops in Brazil. Certainly, both the discovery and description of novel baculoviruses may lead to development of greener and safer pesticides in order to counteract and effectively control crop damage-causing insect populations

A baculovirus-mediated strategy for full-length plant virus coat protein expression and purification

BACKGROUND

Garlic production is severely affected by virus infection, causing a decrease in productivity and quality. There are no virus-free cultivars and garlic-infecting viruses are difficult to purify, which make specific antibody production very laborious. Since high quality antisera against plant viruses are important tools for serological detection, we have developed a method to express and purify full-length plant virus coat proteins using baculovirus expression system and insects as bioreactors.

RESULTS

In this work, we have fused the full-length coat protein (cp) gene from the Garlic Mite-borne Filamentous Virus (GarMbFV) to the 3'-end of the Polyhedrin (polh) gene of the baculovirus Autographa californica multiple nucleopolyhedrovirus (AcMNPV). The recombinant baculovirus was amplified in insect cell culture and the virus was used to infect Spodoptera frugiperda larvae. Thus, the recombinant fused protein was easily purified from insect cadavers using sucrose gradient centrifugation and analyzed by Western Blotting. Interestingly, amorphous crystals were produced in the cytoplasm of cells infected with the recombinant virus containing the chimeric-protein gene but not in cells infected with the wild type and recombinant virus containing the hexa histidine tagged Polh. Moreover, the chimeric protein was used to immunize rats and generate antibodies against the target protein. The antiserum produced was able to detect plants infected with GarMbFV, which had been initially confirmed by RT-PCR.

CONCLUSIONS

The expression of a plant virus full-length coat protein fused to the baculovirus Polyhedrin in recombinant baculovirus-infected insects was shown to produce high amounts of the recombinant protein which was easily purified and efficiently used to generate specific antibodies. Therefore, this strategy can potentially be used for the development of plant virus diagnostic kits for those viruses that are difficult to purify, are present in low titers or are present in mix infection in their plant hosts.

Phylogenetic analysis of Bombyx mori nucleopolyhedrovirus polyhedrin and p10 genes in wild isolates from Guangxi Zhuang Autonomous Region, China

Bombyx mori nucleopolyhedrovirus (BmNPV) is a severe pathogen that seriously impacts the sericulture industry. In this study, 45 wild BmNPV isolates were collected from different silkworm-raising regions in China's Guangxi Zhuang Autonomous Region. Two highly expressed very late genes from each isolate, polyhedrin and p10, were sequenced and subjected to phylogenetic analysis. The polyhedrin gene was found to be highly conserved, while the p10 gene was more variable frequently harboring point mutations and displaying variations in codon use without obvious codon bias. The BmNPV isolates from Guangxi were separated into three main clades, I, II, and III, according to the p10 gene phylogenetic tree. The geographical distribution of clade I isolates in Guangxi showed a concentrated pattern and that of clade II isolates showed a connected pattern. Clade III isolates were irregularly scattered throughout Guangxi. Local transmission of this pathogen clearly occurred in the silkworm-raising regions in Guangxi. This study may provide some data on BmNPV transmission in the silkworm-raising regions and be helpful in devising strategies for the prevention and control of BmNPV disease.

How baculovirus polyhedra fit square pegs into round holes to robustly package viruses

Natural protein crystals (polyhedra) armour certain viruses, allowing them to survive for years under hostile conditions. We have determined the structure of polyhedra of the baculovirus Autographa californica multiple nucleopolyhedrovirus (AcMNPV), revealing a highly symmetrical covalently cross-braced robust lattice, the subunits of which possess a flexible adaptor enabling this supra-molecular assembly to specifically entrap massive baculoviruses. Inter-subunit chemical switches modulate the controlled release of virus particles in the unusual high pH environment of the target insect's gut. Surprisingly, the polyhedrin subunits are more similar to picornavirus coat proteins than to the polyhedrin of cytoplasmic polyhedrosis virus (CPV). It is, therefore, remarkable that both AcMNPV and CPV polyhedra possess identical crystal lattices and crystal symmetry. This crystalline arrangement must be particularly well suited to the functional requirements of the polyhedra and has been either preserved or re-selected during evolution. The use of flexible adaptors to generate a powerful system for packaging irregular particles is characteristic of the AcMNPV polyhedrin and may provide a vehicle to sequester a wide range of objects such as biological nano-particles.