Baculoviral polyhedrin as a novel fusion partner for formation of inclusion body in Escherichia coli.

Baculoviral polyhedrin, which originated from Autographa californica nuclear polyhedrosis virus (AcNPV), was employed for the first time as a novel fusion partner for expression of foreign proteins in an Escherichia coli system. We characterized the expression of recombinant polyhedrin protein fused to green fluorescent protein (GFP). The polyhedrin fusion protein ( approximately 58 kDa) was successfully expressed as an insoluble inclusion body comprising approximately 30% of the total cellular protein. The E. coli expressing polyhedrin-GFP fusion protein showed higher cell growth ( approximately 1.8-fold) and higher GFP yield ( approximately 3.5-fold) than the strain expressing soluble single GFP. Interestingly, the polyhedrin fusion portion showed almost the same characteristics as the native baculoviral polyhedrin; it was rapidly solubilized under alkaline conditions, similar to the conditions found in the insect midgut. In addition, the polyhedrin fusion portion was rapidly digested by alkaline proteases in insect Plutella xylostella midgut as well as by alpha-chymotrypsin, a protease that has similar properties to insect midgut polyhedra-associated alkaline proteases. These unique properties suggest that baculoviral polyhedrin might be an advantageous fusion partner for production of foreign proteins, especially harmful proteins, in E. coli expression systems.