Expression and purification of norovirus virus like particles in Escherichia coli and their immunogenicity in mice

Norovirus (NoV) virus like particles (VLPs) produced in Spodoptera frugiperda (Sf9) cells have been tested in human volunteers as vaccine candidate and were shown to be protective against NoV induced acute gastroenteritis. In this study, prevailing Sydney-2012-like NoV major capsid protein gene with or without N-terminal deletions (N26 and N38, 26 and 38 amino acids deleted from N terminus，respectively) were sub-cloned into prokaryotic expression vector, pCold III and pCold IV. Soluble and insoluble proteins were detected for both vectors after induction and higher levels of protein expression were observed for constructs pCold III-N26 and pCold III-N38. Electron microscopy observation of unpurified and purified lysates indicated in vivo assembly of VLPs with two sizes in accordance with those observed in Sf9 cells. In vitro salivary HBGA-VLP binding assay demonstrated that VLPs assembled in Escherichia coli (E. coli) exhibited the same binding pattern as that of VLPs assembled in Sf9 cells. Immunization of mice with purified VLPs derived from pCold III-N38 demonstrated higher IgG antibody titers and blocking antibody titers when compared with full-length capsid protein assembled VLPs from recombinant baculovirus expression system. In conclusion, NoV VLPs produced in E. coli using pCold expression vector might be used for the development of NoV vaccine.