Expression of the Helicoverpa cathepsin B-like proteinase during embryonic development

Cathepsin B-like proteinase from Helicoverpa armigera (HCB) was proposed as being involved in the degradation of yolk proteins during embryonic development. Recombinant HCB was expressed as a fusion protein with GST in Escherichia coli BL21 on the basis of its cDNA and purified to homogeneity. The fusion protein was cleaved with thrombin to generate a soluble protease with a mass of 37 kDa. A polyclonal antiserum against this recombinant protein, raised in the rabbit, recognized three isoforms of HCB in an ovary homogenate of this insect. Expression of this enzyme during embryonic development was studied using immunoblotting, immunohistochemistry and activity assay. It was found that HCB was expressed during embryonic development and that its proteolytic activity was detected from embryonic developmental eggs. The fact that HCB activity is observed in ovaries and developing eggs suggested that the enzyme had already been activated before embryonic development. Immunohistochemistry indicated that the enzyme was located in follicular cells, the sphere of yolk granules, and the fat bodies of female adult. These lines of evidence suggested strongly that HCB takes part in the degradation of yolk proteins during the development of embryo.