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Autographa californica nuclear polyhedrosis virus, PDV, and ECV viral envelopes and nucleocapsids: structural
1Texas Agricultural Experiment Station, College Station 77843-2475.
Abstract:
Autographa californica nuclear polyhedrosis virus (AcMNPV) infection results in the production of two types of infectious, enveloped viruses. As both of these viral forms play significantly different roles in the virus life cycle, the different functional characteristics in the roles of the virus may be explained, in part, by the protein and lipid composition and source of the viral envelopes. Both viruses utilize different maturation and envelopment strategies: Extracellular virus (ECV) obtains an envelope by budding from the host cell plasma membrane, while the envelope of polyhedra-derived virus (PDV) is obtained within the nucleus of the host cell. There is compelling evidence for differences between ECV and PDV structural proteins; however, no previous study directly compares ECV and PDV purified from the same source and little data are available on the protein and lipid composition of the viral envelopes. This study begins the systematic comparison of ECV, PDV, and their envelopes to target proteins for use as probes to study the molecular and biochemical basis of viral envelopment within the nucleus. AcMNPV ECV and PDV were isolated from infected Spodoptera frugiperda cells and fractionated into their respective envelope and nucleocapsid fractions. The structural protein, glycoprotein, and phosphoprotein composition of ECV, PDV, and their envelope and nucleocapsid fractions are analyzed and compared, and antigens of ECV and PDV viral envelope are identified. A number of structural proteins are different between ECV and PDV. ECV is enriched for proteins at 67, 45, and 35 kDa, while proteins at 89, 70, 60, 50, and 25 kDa are enriched in PDV. At least two proteins, PDV-E66 and PDV-E43, are identified to be specific for the PDV envelope. There are more N-glycosylated proteins in ECV than in PDV, with ECV-specific proteins found at 137, 128, 89, 45, and 40 kDa. PDV glycoproteins are 70, 53, 49, 42, 40, and 31 kDa. Most phosphoproteins of both ECV and PDV are predominantly found in the viral envelopes. The predominant phosphoprotein of ECV is 85 kDa, whereas PDV major phosphoprotein is 36 kDa. This study presents the first report of the phospholipid and fatty acid content of ECV and PDV viral envelopes. The major phospholipid of ECV is phosphatidylserine (50%), while phosphatidylcholine and phosphatidylethanolamine are the major phospholipids of PDV (39 and 30%, respectively). Since PDV is enveloped within the nucleus of the host cell, the PDV phospholipid composition is compared with the phospholipid composition of purified S. frugiperda (Sf9) nuclei and this analysis demonstrates significant differences between these two membrane systems.
Insights
This study reveals distinct protein and lipid compositions in Autographa californica nuclear polyhedrosis virus (AcMNPV) extracellular virus (ECV) and polyhedra-derived virus (PDV) envelopes. These differences, particularly in specific proteins and phospholipids, are crucial for understanding viral envelopment strategies.
Area of Science:
- Virology
- Molecular Biology
- Biochemistry
Background:
- Autographa californica nuclear polyhedrosis virus (AcMNPV) produces two infectious viral forms: extracellular virus (ECV) and polyhedra-derived virus (PDV).
- ECV and PDV utilize different envelopment strategies, with ECV budding from the plasma membrane and PDV acquiring its envelope within the nucleus.
- Understanding the compositional differences in their envelopes is key to elucidating their distinct roles in the viral life cycle.
Purpose of the Study:
- To systematically compare the protein and lipid composition of AcMNPV ECV and PDV envelopes.
- To identify specific viral envelope proteins and understand their roles in viral envelopment.
- To provide insights into the molecular and biochemical basis of viral envelopment within the nucleus.
Main Methods:
- Isolation and fractionation of AcMNPV ECV and PDV from infected Spodoptera frugiperda cells into envelope and nucleocapsid components.
- Analysis and comparison of structural proteins, glycoproteins, and phosphoproteins.
- Identification of specific viral envelope antigens.
- Analysis of phospholipid and fatty acid content of viral envelopes.
- Comparison of PDV envelope phospholipids with host cell nuclear membranes.
Main Results:
- Significant differences were observed in the protein composition of ECV and PDV envelopes.
- ECV envelopes were enriched in proteins at 67, 45, and 35 kDa, while PDV envelopes showed enrichment in proteins at 89, 70, 60, 50, and 25 kDa.
- Specific PDV envelope proteins (PDV-E66 and PDV-E43) were identified.
- ECV envelopes contained more N-glycosylated proteins than PDV envelopes.
- Distinct major phosphoproteins were identified for ECV (85 kDa) and PDV (36 kDa).
- The phospholipid composition differed significantly, with ECV major phospholipid being phosphatidylserine (50%) and PDV major phospholipids being phosphatidylcholine (39%) and phosphatidylethanolamine (30%).
- PDV envelope phospholipids showed significant differences compared to purified Sf9 cell nuclei.
Conclusions:
- The distinct protein and lipid profiles of ECV and PDV envelopes reflect their different origins and functions.
- Specific proteins identified in PDV envelopes can serve as targets for studying nuclear viral envelopment.
- The unique phospholipid composition of PDV envelopes suggests specific membrane interactions or modifications occurring within the nucleus.
- This study provides a foundation for understanding the molecular mechanisms underlying AcMNPV morphogenesis and infection.