Truncated expression of porcine delta coronavirus protein NSP14 and establishment of indirect ELISA antibody detection method

【Objective】The truncated NSP14 protein of porcine delta coronavirus(PDCoV) was expressed in prokaryotic,and the polyclonal antibody of PDCoV NSP14 protein was prepared,and an indirect enzyme-linked immunosorbent assay (ELISA) method for detecting PDCoV antibody was established.It provided a reference for exploring the biological function of PDCoV NSP14 protein and conducting PDCoV monitoring and diagnosis.【Method】In this study,the prokaryotic recombinant plasmid pET32a-NSP14 of NSP14 truncated gene was constructed using PDCoV 1468B strain as a template,and after identified by double digestion and sequencing,the recombinant protein pET32a-NSP14 was obtained by prokaryotic expression system.They were purified and then reimmunized to New Zealand white rabbits to obtain polyclonal antibodies against NSP14 protein,the Western blotting was performed and and its titer was determined by indirect ELISA method.NSP14 recombinant protein was used as antigen coated enzyme-linked immunosorbent assay plate,and a series of reaction conditions were optimized by square matrix titration method to construct an indirect ELISA method for detecting PDCoV antibody.【Result】The recombinant plasmid pET32a-NSP14 was constructed successfully,and the NSP14 protein was expressed as an inclusion body in Escherichia coli BL21(DE3) competent cells with a size of approximately 40.2 kD.The NSP14 protein polyclonal antibody was produced successfully,with an antibody titer above 1∶512000,and it could specifically react with the purified recombinant NSP14 protein.After screening,the optimal reaction conditions of the indirect ELISA antibody detection method were determined:the optimal coating concentration of NSP14recombinant protein was 4.0μg/mL,and the coating condition was 37℃for 2.0 h;the blocking condition was 5%skimmed milk powder for 1.0 h;the serum to be tested was diluted 1∶400 and incubated for 2.0 h;the enzyme labeled secondary antibody was diluted 1∶2500 and incubated for 60.0 min;the TMB substrate reaction time was 30.0 min.The results of specificity test showed that the OD₄₅₀ values of PRRSV,JEV,PCV2,PPV,PEDV and CSFV in the positive serum of porcine disease were less than 0.235,indicating that the optimized ELISA method did not react with other positive serum of porcine virus and had good specificity.The repeatability test results showed that the intraassay and inte-rassay coefficients of variation of the optimized ELISA method for detecting pig positive serum were less than 10.000%,indicating that the optimized ELISA method had good repeatability.【Conclusion】In this study,the polyclonal antibody of PDCoV NSP14 protein with high titer and good immunoreactivity has been successfully prepared,and an indirect ELISA antibody detection method with good specificity,sensitivity and repeatability is established,which provides reference for further study of the biological function of PDCoV NSP14 protein and PDCoV monitoring and diagnosis.