Cloning and expression of hepatitis E virus ORF2 as an immunogen protein in baculovirus expression system

Hepatitis E virus (HEV) is a non-enveloped, single-stranded positive-sense RNA virus. It is one of the most important causes of liver failures and the mortality rate arising from HEV is more common in pregnant women. HEV is an enterically-transmitted virus and its outbreak is more common in the developing and poor-hygiene countries while vaccination against it can prevent its prevalence. The ORF2 is an immunogenic capsid protein of HEV with 660 amino acids that is being used in vaccine designs against HEV infection. ORF2 has been studied in a vast range of vectors and hosts, such as pRSET-C, pMAL and pSG vectors, as well as Escherichia coli BL21 and vaccinia virus hosts. A DNA vaccine expressing ORF2 has also been studied which has induced specific humoral and cellular immune responses in mice. This study was aimed to clone and express ORF2 as an immunogen protein in a eukaryotic host system. orf2 gene corresponding to 660 amino acids of ORF2 protein was subcloned from a pET21avector into pFastBac. The protein expression was achieved by transforming Sf9 insect cells with a pFastBac-orf2 construct. The over-expressed protein with ~72 kDa MW was assessed by SDS-PAGE. The cloning was confirmed by PCR and restriction digestions. The expression of ORF2 with expected MW in Sf9 cells was confirmed by SDS-PAGE. ORF2 protein of HEV was successfully expressed in a baculovirus-based eukaryotic expression system as the first step for further studies on HEV vaccine designs, based on ORF2 protein.