Enhancing yield of infectious bursal disease virus structural proteins in baculovirus expression systems: Focus on media, protease inhibitors, and dissolved oxygen

Structural proteins of the poultry pathogen, infectious bursal disease virus (IBDV), were expressed in the baculovirus/insect cell expression system. To date, several reports have indicated that animal virus structural proteins are expressed only at low yield in this system. In this article, several factors were examined to enhance yield. These include medium, dissolved oxygen level, and the addition (in vivo and in vitro) of protease inhibitors. Specifically, two media were compared, and SF-900 II was superior to Ex-Cell 401 for cell growth and IBDV protein expression. A cocktail of protease inhibitors including phenylmethyl sulfonyl fluoride (PMSF), leupeptin, and ethylenediamine tetraacetic acid (EDTA) minimized proteolysis in vitro. Also, aprotinin and pepstatin A deterred product degradation in vivo and increased the product yield nearly 2-fold. Finally, in 3 L bioreactors, a dissolved oxygen tension of 50% DO (air saturation) was optimal. Results demonstrated that several relatively simple adjustments to the baculovirus system significantly improved the yield of IBD virus structural proteins.