Codon Optimization and Expression of Norovirus apsid Proteins in Insect Cells

Norovirus is currently the predominant human calicivirus that causes diarrhea in China. Among the documented noroviruses, types 4, 1 and 3 are the leading genetics groups. In order to improve the expression of the norovirus capsid, we re-designed and artificially synthesized the full-length norovirus capsid genes by adopting the codons preferentially used in insect cells without any changing of the amino acid sequences. The codon optimized capsid genes of Norovirus GGII1, GGII3, GGII4 and GGII7 were respectively expressed in insect cell Sf9 using baculovirus vector. The results showed that, compared to the wild type, the expression levels of the optimized genes were remarkably increased. The assembly of norovirus-like particles was observed in the Sf9 cells infected with the recombinant baculovirus expressing the capsid protein. The recombinant capsid expression peaked at 72h post infection of the recombinant baculoviruses. The results obtained in the present work will lay a foundation for the development of the immunological diagnostic reagents as well as vaccines for human caliciviruses.