Molecular cloning, sequencing, and biological characterization of GRA4 gene of Toxoplasma gondii

Single Cell Expression Systems for the Production of Recombinant Proteins for Immunodiagnosis and Immunoprophylaxis of Toxoplasmosis

Toxoplasmosis represents a significant public health and veterinary concern due to its widespread distribution, zoonotic transmission, and potential for severe health impacts in susceptible individuals and animal populations. The ability to design and produce recombinant proteins with precise antigenic properties is fundamental, as they serve as tools for accurate disease detection and effective immunization strategies, contributing to improved healthcare outcomes and disease control. Most commonly, a prokaryotic expression system is employed for the production of both single antigens and multi-epitope chimeric proteins; however, the cloning strategies, bacterial strain, vector, and expression conditions vary. Moreover, literature reports show the use of alternative microbial systems such as yeast or Leishmania tarentolae. This review provides an overview of the methods and strategies employed for the production of recombinant Toxoplasma gondii antigenic proteins for the serological detection of T. gondii infection and vaccine development.

Cloning and expression of Toxoplasma gondii GRA-4 recombinant protein as a toxoplasmosis diagnostic kit candidate

Aim:

The objective of this study was to produce recombinant protein GRA-4 (rGRA-4) of a local Toxoplasma gondii isolate as a candidate for a toxoplasmosis diagnosis kit in Escherichia coli BL21 (DE3) competent cells using pET SUMO plasmid.

Materials and Methods:

Samples used were stock T. gondii tachyzoites DNA from the Parasitology Laboratory, Faculty of Veterinary Medicine, Gadjah Mada University, Yogyakarta. Amplified GRA-4 polymerase chain reaction product of T. gondii tachyzoite DNA was cloned in the pET-SUMO TA^R cloning vector. The GRA-4 gene from T. gondii local isolate was sequenced, followed by plasmid transformation, recombinant plasmid DNA isolation, and recombinant protein expression in DE3 competent cells.

Results:

The amplification product of GRA-4T. gondii gene was 1036 bp, with 48 kDa molecular weight after expression in DE3 competent cells. An alignment of the amino acid sequence of GRA-4 from the local isolate which was cloned with GRA-4 was obtained from NCBI database and showed 99.61% homology to the predicted GRA-4 from the T. gondii Izatnagar isolate. Amino acid sequence of the predicted GRA-4 protein from local isolate was different at positions 19 and 304.

Conclusion:

This research cloned rGRA-4 in pET SUMO plasmid.

Structural predication and antigenic analysis of Toxoplasma gondii ROP20

Toxoplasma gondii infects almost all the warm-blooded animals. ROP20 protein is expressed in the rhoptry of Toxoplasma gondii. In this study, the secondary structure of ROP20 was analyzed using SMART software. We constructed and analyzed the 3D model of ROP20 protein using SWISS-MODEL online procedure and Visual Molecular Dynamics (VMD) software. The structure analysis fully indicated that ROP20 protein is an important member of the ROP family. Furthermore, We used DNASTAR software and Epitope Database online service to analyze liner-B cell epitopes and T-cell epitopes of ROP20 protein. All the analysis results of ROP20 protein can provide positive information on treatment and vaccine for toxoplasmosis. Moreover, ROP20 gene was obtained from PCR, and a recombinant eukaryotic expression vector (pEGFP-C1-ROP20) was constructed in the following study. After restriction enzyme digestion, the constructed plasmid was transfected into HEK 293-T cells. The RT-PCR result indicated that the recombinant plasmid could transcribe successfully in HEK 293-T cell. The results of western blotting indicated the expressed proteins can be recognized by anti-STAg mouse sera.

Analyzing and identifying novel B cell epitopes within Toxoplasma gondii GRA4

Background

The identification of specific epitopes targeted by the host antibody response is important for understanding the natural response to infection and for the development of epitope-based marker vaccines and diagnostic tools for toxoplasmosis. In this study, Toxoplasma gondii GRA4 epitopes were identified using software-based prediction and a synthetic peptide technique.

Methods

The complete GRA4 gene sequence was obtained from T. gondii of the Gansu Jingtai strain of tachyzoites. The potential B cell epitopes of GRA4 was predicted using the PROTEAN subroutine in the DNASTAR software package. The peptides with good hydrophilicity, high accessibility, high flexibility and strong antigenicity were chemically synthesized and assessed by ELISA using pig sera from different time points after infection.

Results

The potential B cell epitopes of GRA4 predicted by bioinformatics tools focused on six regions of GRA4, 52–77 aa, 93–112 aa, 127–157 aa, 178–201 aa, 223–252 aa and 314–333 aa. Eleven shorter peptides from the six regions were synthesized and assessed by ELISA using pig sera from different time points after infection. Three of the eleven peptides (amino acids 62–77, 233–252 and 314–333) tested were recognized by all sera.

Conclusions

We precisely located the T. gondii GRA4 epitopes using pig sera collected at different time points after infection. The identified epitopes may be useful for additional studies of epitope-based vaccines and diagnostic reagents.

Immunization with excreted-secreted antigens reduces tissue cyst formation in pigs

It has been demonstrated that tachyzoite-pooled excreted-secreted antigens (ESAs) of Toxoplasma gondii are highly immunogenic and can be used in vaccine development. However, most of the information regarding protective immunity induced by immunization with ESAs is derived from studies using mouse model systems. These results cannot be extrapolated to pigs due to important differences in the susceptibility and immune response mechanisms between pigs and mice. We show that the immunization of pigs with ESAs emulsified in Freund's adjuvant induced not only a humoral immune response but also a cellular response. The cellular immune response was associated with the production of IFN-γ and IL-4. The humoral immune response was mainly directed against the antigens with molecular masses between 34 and 116 kDa. After intraperitoneal challenge with 10(7) T. gondii of the Gansu Jingtai strain (GJS) of tachyzoites, the immunized pigs remained clinically normal except for a brief low-grade fever (≤40.5 °C), while the control pigs developed clinical signs of toxoplasmosis (cough, anorexia, prostration, and high fever). At necropsy, visible lesions were found at multiple locations (enlarged mesenteric lymph nodes, an enlarged spleen with focal necrosis, and enlarged lungs with miliary or focal necrosis and off-white lesions) in all of the control pigs but not in the pigs that had been immunized. We also found that immunization with ESAs reduced tissue cyst formation in the muscle (P < 0.01). Our data demonstrate that immunization with ESAs can trigger a strong immune response against T. gondii infection in pigs.