Autographa californica nuclear polyhedrosis virus, PDV, and ECV viral envelopes and nucleocapsids: structural proteins, antigens, lipid and fatty acid profiles

Autographa californica nuclear polyhedrosis virus (AvMNPV) 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 date 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.