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Cytotoxic T lymphocyte-associated antigen 4 (CTLA-4) is an important surface molecule of activated T cells that has a strong affinity with the B7 molecule on the surface of antigen-presenting cells. Among these molecules, the CTLA-4 extracellular region (CTLA-4 IgV) may be used as a novel immune adjuvant molecule for delivering antigens and inducing strong humoral and cellular immune responses. In this study, bioinformatics analysis was performed to determine and clone the extracellular region of Xinjiang sheep CTLA-4 (NM_001009214). The CTLA-4 IgV gene was amplified and ligated into the pMD19-T vector, and the positive bacteria were screened by blue-white spots for sequencing and comparison. The correctly sequenced CTLA-4 IgV was digested and then ligated into the prokaryotic expression vector pET-30a(+). The plasmid pET30a–CTLA-4 IgV was constructed to induce the expression of the recombinant protein CTLA-4 IgV. Thereafter, CTLA-4 IgV was identified. Clustal X multiple sequence alignment revealed that the protein sequence of Xinjiang sheep CTLA-4 IgV was different from that of the known CTLA-4 extracellular region. The 3D protein structure of Xinjiang sheep CTLA-4 IgV was constructed via the bioinformatics method. Subsequently, molecular docking between the Xinjiang sheep CTLA-4 IgV protein and the B7 molecule was conducted. Results revealed multiple binding sites in the extracellular region of Xinjiang sheep CTLA-4, and two multiple interactions ensured stable binding after docking. The functionality of the Xinjiang sheep CTLA-4 IgV protein was further verified by fusing the CTLA-4 extracellular V region with EgG1Y162, a protective protein fromEchinococcus granulosa, and the purified recombinant protein CTLA-4 IgV–EgG1Y162 was expressed with the mouse bone marrow-derived. The addition of the Xinjiang sheep CTLA-4 IgV protein at the amino terminus promoted the binding of EgG1Y162 to dendritic cells (DCs) and increased the maturation rate of these cells, further indicating that the protein could effectively improve the antigen presentation ability of DCs. The CTLA-4 extracellular domain protein of Xinjiang sheep is unique and has the potential to promote the presentation of the fusion protein by DCs as an adjuvant. The cloning and expression of this gene provide new measures and ideas for the preparation of the Xinjiang sheep vaccine to prevent zoonotic diseases.

In the early stage, our research group cloned Echinococcus granulosus-specific antigen, EgG1Y162, from protoscolex and adult worms of E. granulosus. In order to enhance the immunogenicity of the vaccine, we prepared a recombinant vaccine by tandemly linking EgG1Y162, splicing the protein and linker at the gene level. This approach is expected to improve the immunogenicity of the vaccine by enhancing the molecular weight of the protein and increasing the antigenic epitopes. Bioinformatics was used to predict the physicochemical properties, transmembrane domain, protein structure, and T-/B-cell antigenic epitope of different recombinant proteins, EgG1Y162-linker-EgG1Y162. Finally, the linker sequence, “GGGGSGGG,” which had the least influence on the migration of recombinant protein T/B epitope and can fold normally in series with EgG1Y162, was selected to design the recombinant vaccine. The plasmid was produced using genetic engineering techniques, and the recombinant protein, EGG1Y162-GGGGSGGG-EgG1Y162, was induced to be expressed and purified. EgG1Y162-GGGGSGGG-EgG1Y162 was identified to be correctly expressed with 100% specificity. Compared with EgG1Y162, EgG1Y162-GGGGSGGG-EgG1Y162 was more likely to promote dendritic cell maturation. EgG1Y162-GGGGSGGG-EgG1Y162 was speculated to have the potential to improve antigen immunogenicity by increasing the molecular weight and antigenic epitope.