Intracellular manipulation of disulfide bond formation in rotavirus proteins during assembly.

Rotavirus undergoes a unique mode of assembly in the rough endoplasmic reticulum (RER) of infected cells. Luminal RER proteins undergo significant cotranslational and posttranslational modifications, including disulfide bond formation. Addition of a reducing agent (dithiothreitol [DTT]) to rotavirus-infected cells did not significantly inhibit translation or disrupt established disulfide bonds in rotavirus proteins but prevented the formation of new disulfide bonds and infectious viral progeny. In DTT-treated, rotavirus-infected cells, all vp4, vp6, and ns28 epitopes but no vp7 epitopes were detected by immunohistochemical staining with a panel of monoclonal antibodies. When oxidizing conditions were reestablished in DTT-treated cells, intramolecular disulfide bonds in vp7 were rapidly and correctly established with the restoration of antigenicity, although prolonged DTT treatment led to the accumulation of permanently misfolded vp7. Electron microscopy revealed that cytosolic assembly of single-shelled particles and budding into the ER was not affected by DTT treatment but that outer capsid assembly was blocked, leading to the accumulation of single-shelled and enveloped intermediate subviral particles in the RER lumen.