Abstract: 【Objective】 The aim of this study was to clone the serine/threonine protein phosphatase 2A (Ser/Thr protein phosphatases 2A,PP2A) gene of Fasciola gigantica and construct a prokaryotic expression vector to obtain the prokaryotic expression protein,so as to lay a foundation for exploring the function of PP2A gene and its role in the development of Fasciola gigantica.【Method】 Total RNA was extracted from adult trematodes,the complete coding region of PP2A gene was amplified by RT-PCR and ligated to pET-28a(＋) vector by double restriction endonuclease digestion and sequencing,the positive plasmid was named as recombinant plasmid pET-28a-PP2A.The recombinant plasmid pET-28a-PP2A was transformed into E.coli expression strain BL21 (DE3) competent cell for IPTG induction,and the induction conditions of the recombinant protein were optimized.The expression effect of PP2A gene of Fasciola gigantica was detected by SDS-PAGE and Western blotting.Real-time PCR was used to detect the expression of PP2A gene in eggs,metacercaria,6-week-old juvenile and adults of Fasciola gigantica.【Result】 The coding region of PP2A gene of Fasciola gigantica was 1 161 bp,encoding 386 amino acids.The molecular formula was C₁₉₈₀H₃₁₀₅N₅₃₅O₅₆₆S₂₄ and the molecular weight was 44.23 ku.The results of bioinformatics analysis showed that the protein edited by PP2A gene was PP2Ac,the molecular function was signal transduction (GO:0004871),the biological process was protein dephosphorylation (GO:0006470),and the cell component was cytoplasm (GO:0005829).PP2A protein had no signal peptide and no transmembrane domain.It was a hydrophilic protein with 37 phosphate sites.The results of SDS-PAGE and Western blotting showed that the expression of PP2A in Fasciola gigantica was the highest at 30 ℃ and 0.8 mmol/L IPTG inducing for 6 h.The expressed product was mainly in the form of inclusion body,and the recombinant protein could be recognized by anti-His tag by Western blotting detection.The results of Real-time PCR showed that the expression of PP2A gene was the highest in the 6-week-old juvenile stage,which was extremely significant higher than that in other stages (P＜0.01),and the lowest in the metacercaria stage,and had no significant difference with the egg stage(P＞0.05).【Conclusion】 In this study,the prokaryotic expression vector of Fasciola gigantica PP2A was successfully constructed and the corresponding protein was obtained,which laid a foundation for studying the function of PP2A gene in the growth and development of Fasciola gigantica.

Key words: Fasciola gigantica; serine/threonine protein phosphatase 2A (PP2A); prokaryotic expression