Reduced redox potential of the cytosol is important for African swine fever virus capsid assembly and maturation

Assembly of African swine fever virus (ASFV) involves the transfer of the major capsid protein, p73, from the cytosol onto the cytoplasmic face of endoplasmic reticulum-derived membranes. During this process, the folding of p73 is dependent upon transient association with a specific viral chaperone, CAP80. The cell cytoplasm maintains high concentrations of reduced glutathione, leading to a reducing environment. Here, the effects of redox environment on the assembly of ASFV have been studied. Diamide, which oxidizes the cell cytosol, slowed the folding of p73 and prevented release from CAP80 and subsequent binding of p73 to membranes. Similarly, cell oxidation slowed the assembly of p73 molecules already bound to membranes into virus capsid precursors. Interestingly, addition of oxidized glutathione to newly assembled virus capsid precursors in vitro led to disassembly; however, virus particles released from cells were resistant to oxidized glutathione. These data show that assembly of ASFV requires the reducing environment that prevails in the cytosol, but as the virus matures, it becomes resistant to oxidation, possibly indicating preparation for release from the cell.