Summary auto-generated
Researchers expressed the spheroidin gene from Amsacta moorei entomopoxvirus (AmEPV) in insect cells using a baculovirus vector. Spheroidin is the major protein component of viral occlusion bodies called spheroids. When produced in Spodoptera frugiperda and Trichoplusia ni cells, spheroidin spontaneously assembled into large, ovoid structures resembling natural spheroids but lacking viral particles and surrounding membranes. Western blotting and immunofluorescence confirmed spheroidin protein synthesis. Transmission electron microscopy and cell fractionation experiments revealed a surprising finding: spheroid-like structures assembled in both the nucleus and cytoplasm of recombinant virus-infected cells, contrasting with the exclusively cytoplasmic localization in natural AmEPV infections. These results demonstrate that spheroidin possesses intrinsic properties enabling self-assembly into crystalline occlusion-body-like structures independent of other viral gene products. The assembly mechanism resembles polyhedrin self-assembly in other viruses. However, the actual occlusion of mature virus particles into spheroids appears to require additional viral components beyond spheroidin alone. The unexpected nuclear localization of spheroid-like structures in baculovirus-infected cells remains unexplained but may involve cytoskeletal rearrangements.
Key findings
- AmEPV spheroidin protein can self-assemble into spheroid-like occlusion bodies without other viral gene products or viral particles
- Spheroidin assembled in both nuclear and cytoplasmic compartments of recombinant baculovirus-infected cells, unlike the exclusively cytoplasmic localization in natural infections
- The spheroid-like structures lacked occluded virions and envelope-like structures, indicating that mature spheroid formation requires additional viral components
- Spheroidin self-assembly and viral particle occlusion appear to be distinct, sequential processes in mature spheroid formation
This summary was generated automatically from the article PDF and is not part of the original publication. Refer to the PDF for the authoritative text.
Abstract
The gene encoding the major occlusion body protein, spheroidin, of Amsacta moorei entomopoxvirus (AmEPV) was introduced into a baculovirus vector under control of the polyhedrin gene promoter. A recombinant virus produced large, ovoid occlusion body-like structures in both Spodoptera frugiperda and Trichoplusia ni cells. These structures resembled the spheroids found in AmEPV-infected Lymantria dispar cells, except they were devoid of virus particles and were not surrounded by a membrane- or envelope-like structure. These results were confirmed by immunofluoresence microscopy and Western blotting using a specific antipeptide antibody to spheroidin, and suggest that the supramolecular assembly of spheroids is not dependent on other EPV-encoded gene products. Transmission electron microscopy and subcellular fractionation experiments revealed that the spheroid-like structures were assembled in both the nucleus and cytoplasm of the recombinant virus-infected cells. This contrasts with the solely cytoplasmic localization found in AmEPV-infected cells.