The baculovirus expression vector system (BEVS) is extensively used to produce recombinant proteins due to its high rate of expression. The major drawback of using this system is the early cell death (typically after 48-72 h post infection) that leads to decreased recombinant protein expression. Viral infection increases the production of reactive oxygen species (ROS) that are believed to contribute to this early cell death. Baculoviruses contain a Copper-Zinc Superoxide Dismutate (CuZnSOD) homolog gene that inactivates cellular CuZnSOD activity in insect cells by ~48 h post infection. Specifically, the CuZnSOD homolog inactivates the CuZnSOD enzyme by binding the copper chaperone, thereby leading to increased oxidative stress and presumably more rapid cell death. CuZnSOD activity during Wt-AcMNPV infection decreased to 0 in about 48-60 h post infection.
In this study the Autographa californica multiple nucleopolyhedrovirus (AcMNPV) modified to overexpress human CuZnSOD and Copper chaperone cassette (CCS) and devoid of the viral CuZnSOD homolog showed lower infectivity compared to Wt- AcMNPV infection. Futhermore, the addition of H2O2 to induce oxidative stress increased the infectivity of the modified AcMNPV, thereby supporting the premise that a minimal level of oxidative stress is required for improved infection. Further investigations are required to determine if this modified virus would be a better expression vector then the conventionally used baculovirus vectors.