Efficient soluble protein production on transgenic silkworms expressing cytoplasmic chaperones

Baculovirus expression systems (BES) are widely used for recombinant protein production in lepidopteran cells or larvae. However, even in BES, the insolubility of recombinant proteins sometimes makes their expression difficult. In this study, to improve the solubility and yield of foreign proteins, we constructed transgenic silkworms using silkworm heat-shock proteins, Hsp70 and Hsp40, or Hsc70 and Hsp90 co-chaperone Hop. In these transgenic silkworms, the expression levels of the transgenes were under the control of a UAS·hsp mini-promoter driven by a Gal4NFkBp65 activator. When the transgenic silkworm with HSP70 and 40 (TGS-HSP70/40) was infected with BmNPV carrying mC3d and Gal4NFkBp65 under the control of baculovirus polyhedrin or p10 promoters, respectively, the soluble fraction of the His- or His·GST-tagged mC3d increased significantly. Similarly, the transgenic silkworm with HSC70 and HOP (TGS-HOP7) was effective for the expression of a steroid hormone receptor, USP2. In conclusion, the His-tagged baculovirus expression system featuring the chaperone effect TGS-HSP70/40 and TGS-HOP7 silkworms is effective for increasing the yields of soluble and functional foreign gene products.