Identification of fragments from Autographa Californica polyhedrin protein essential for self-aggregation and exogenous protein incorporation

BACKGROUND: Baculoviruses are widely used for the production of recombinant proteins, biopesticides and as gene delivery systems. One of the viral forms called polyhedra has been recently exploited as a scaffold system to incorporate or encapsulate foreign proteins or peptide fragments. However, an efficient strategy for foreign protein incorporation has not been thoroughly studied. RESULTS: Based on the crystal structure of polyhedrin, we conducted an in silico analysis of the baculovirus Autographa californica nucleopolyhedrovirus (AcMNPV) polyhedrin protein to select the minimum fragments of polyhedrin that could be incorporated into polyhedra. Using confocal and transmission electron microscopy we analyzed the expression and cellular localization of the different polyhedrin fragments fused to the green fluorescent protein (EGFP) used as reporter. The amino fragment 1–110 contains two repeats formed each of two β sheets followed by a α helix (amino acids 1–58 and 58–110) that are important for the formation and stability of polyhedra. These fragments 1–58, 58–110 and 1–110 could be incorporated into polyhedra. However, only fragments 1–110 and 58–110 can self-aggregate. CONCLUSIONS: These results demonstrate that 58–110 is the minimum fragment that contributes to the assembly of the recombinant polyhedra via self-aggregation. This is the minimum sequence that can be used to efficiently incorporate foreign proteins into polyhedra.