Biochemical Characterization and Functional Analysis of Glucose Regulated Protein 78 from the Silkworm Bombyx mori

Abstract

The glucose regulated protein (GRP78) is an important chaperone for various environmental and physiological stimulations. Despite the importance of GRP78 in cell survival and tumor progression, the information regarding GRP78 in silkworm Bombyx mori L. is poorly explored. We previously identified that GRP78 expression was significantly upregulated in the silkworm Nd mutation proteome database. Herein, we characterized the GRP78 protein from silkworm B. mori (hereafter, BmGRP78). The identified BmGRP78 protein encoded a 658 amino acid residues protein with a predicted molecular weight of approximately 73 kDa and comprised of two structural domains, a nucleotide-binding domain (NBD) and a substrate-binding domain (SBD). BmGRP78 was ubiquitously expressed in all examined tissues and developmental stages by quantitative RT-PCR and Western blotting analysis. The purified recombinant BmGRP78 (rBmGRP78) exhibited ATPase activity and could inhibit the aggregating thermolabile model substrates. Heat-induction or Pb/Hg-exposure strongly stimulated the upregulation expression at the translation levels of BmGRP78 in BmN cells, whereas no significant change resulting from BmNPV infection was found. Additionally, heat, Pb, Hg, and BmNPV exposure resulted in the translocation of BmGRP78 into the nucleus. These results lay a foundation for the future identification of the molecular mechanisms related to GRP78 in silkworms.

Effect of acute exposure of Hg on physiological parameters and transcriptome expression in silkworms (Bombyx mori)

“…Notably, Hsc70-4 demonstrated an up-regulated expression in the fat body, a phenomenon associated with Bombyx mori nucleopolyhedrovirus (BmNPV) infection, as reported previously ( 59–61 ). In our previous research, we observed an induction in the translational level of BmGRP78 (also known as Hsc70-3 ) and its translocation into the cell nucleus following Hg exposure ( 62 ). These results demonstrated that these HSP proteins may be functionally related to Hg exposure.…”