Abstract

Background: Toxoplasmosis is a cosmopolitan infectious disease in warmblooded mammals that poses a serious worldwide threat due to the lack of effective medications and vaccines.

Aims: The purpose of this study was to design a multi-epitope vaccine using several bioinformatics approaches against the antigens of Toxoplasma gondii (T. gondii).

Methods: Three proteins of T. gondii, including ROP18, MIC4, and SAG1 were analyzed to predict the most dominant B- and T-cell epitopes. Finally, we designed a chimeric immunogen RMS (ROP18, MIC4, and SAG1) using some domains of ROP18 (N377-E546), MIC4 (D302-G471), and SAG1 (T130-L299) linked by rigid linker A (EAAAK) A. Physicochemical properties, secondary and tertiary structure, antigenicity, and allergenicity of RMS were predicted utilizing immunoinformatic tools and servers.

Results: RMS protein had 545 amino acids with a molecular weight (MW) of 58,833.46 Da and a theoretical isoelectric point (IP) of 6.47. The secondary structure of RMS protein contained 21.28% alpha-helix, 24.59% extended strand, and 54.13% random coil. In addition, evaluation of antigenicity and allergenicity showed the protein to be an immunogen and nonallergen. The results of the Ramachandran plot indicated that 76.4%, 12.9%, and 10.7% of amino acid residues were incorporated in the favored, allowed, and outlier regions respectively. ΔG of the best-predicted mRNA secondary structure was −593.80 kcal/mol which indicates a stable loop is not formed at the 5′ end.

Conclusion: Finally, the accuracy and precision of the in silico analysis must be confirmed by successful heterologous expression and experimental studies.

Keywords: Toxoplasma gondii, ROP18, MIC4, SAG1, in silico, vaccine.

Graphical Abstract