RESUMEN
Objective To clone and express a high mobility group box 1(HMGB1)protein of Schistosoma japonicum(Main-land strain)and analyze its function. Methods The DNA fragment of open reading frame encoding Sj HMGB1 protein was ampli-fied by RT-PCR from the mRNA of S. japonicum worms,then it was subcloned into the expression vector pET28a(+)to form the recombinant expression plasmid SjHMGB1-pET28a. The recombinant expression plasmid was transformed into the component E. coli BL21(DE3),and the tranformant containing recombinant expression plasmid was induced with IPTG to express the recombi-nant protein SjHMGB1. The recombinant SjHMGB1 protein was purified by affinity chromatography with nickel chelating affinity chromatography agarose gel. The Gel retard experiment and animal immunization were performed to analyze the DNA binding ca- pacity and the immunologic property of recombinant SjHMGB1. The expression levels of HMGB1 in different life cycle stages of S. japonicum were analyzed by Western bloting and RT-PCR. Female ICR mice were immunized with the recombinant SjHMGB1 pro-tein and infected with 45±2 cercariae of S. japonicum after three immunizations. Forty-two days post-infection,the worms and eggs of S. japonicum were recovered from the portal vein and liver tissue,respectively. The worm and egg reduction rates were calculat-ed respectively. Results A 530 bp of specific DNA fragment was amplified from mRNA of S. japonicum by RT-PCR,which was the open reading frame(ORF)encoding SjHMGB1protein confirmed by DNA sequencing analysis. The recombinant expression plasmid SjHMGB1-pET28a was constructed by cloning the ORF of SjHMGB1 into a expression vector pET28a(+). The bacterium transformants containing the recombinant plasmid expressed a soluble recombinant protein about 28 kDa after induced by IPTG, and the recombinant SjHMGB1 protein was purified by nickel chelating affinity chromatography. The gel retard experiment showed that the recombinant SjHMGB1 protein could bind to both supercoiled DNA and linear DNA,and the recombinant protein immu-nized mice produced high titers of antiserum IgG. Western bloting indicated that the recombinant SjHMGB1 protein was recognized specifically by the S. japonicum-infected mice serum. Above results showed that the recombinant SjHMGB1 protein possessed both functional activity and immunogenicity as the natural protein. RT-PCR and Western blot results showed that SjHMGB1 was abun-dantly expressed in the adult and egg stages whereas barely detectable in the cercaria stage. The immune protection experiment showed that the recombinant SjHMGB1 induced mice to produce high titers of specific antibody IgG but failed to conduct an effec-tive immune protection against S. japonicum. Conclusion The gene encoding HMGB1 from S. japonicum and the soluble recombi-nant SjHMGB1 protein with natural functional activity are obtained,and the recombinant SjHMGB1 has a high immunogenicity but is not able to induce an effective immune protection against S. japonicum.