Nonvirus encoded proteins could be embedded into Bombyx mori cypovirus polyhedra

To explore whether the nonvirus encoded protein could be embedded into Bombyx mori cypovirus (BmCPV) polyhedra. The stable transformants of BmN cells expressing a polyhedrin (Polh) gene of BmCPV were constructed by transfection with a non-transposon derived vector containing a polh gene. The polyhedra were purified from the midguts of BmCPV-infected silkworms and the transformed BmN cells, respectively. The proteins embedded into polyhedra were determined by mass spectrometry analysis. Host derived proteins were detected in the purified polyhedra. Analysis of structure and hydrophilicity of embedded proteins indicated that the hydrophilic proteins, in structure, were similar to the left-handed structure of polyhedrin or the N-terminal domain of BmCPV structural protein VP3, which were easily embedded into the BmCPV polyhedra. The lysate of polyhedra purified from the infected transformation of BmN cells with modified B. mori baculovirus BmPAK6 could infect BmN cells, indicating that B. mori baculovirus could be embedded into BmCPV polyhedra. Both the purified polyhedra and its lysate could be coloured by X-gal, indicating that the β-galactosidase expressed by BmPAK6 could be incorporated into BmCPV polyhedra. These results suggested that some heterologous proteins and baculovirus could be embedded into polyhedra in an unknown manner.