An in silico Design, Expression and Purification of a Chimeric Protein as an Immunogen Candidate Consisting of IpaD, StxB, and TolC Proteins from Shigella spp.

Background: Shigella spp. is the cause of dysentery and is widespread worldwide. On the other hand, antibiotic resistance is increasing in this bacterium. Bioinformatics is a new approach to vaccine and drug design involving the selection of appropriate antigens. This study aimed to design a chimeric protein consisting of IpaD, StxB, and TolC proteins from Shigella through a bioinformatics approach as an immunogen candidate. Methods: The sequences of ipaD, stxB, and tolC genes were obtained. Additionally, the immunogenic regions of the associated protein, physicochemical characteristics, protein structures, B and T cells epitopes, and molecular docking were determined using in silico servers. Besides, the chimeric gene was synthesized following sequence optimization by utilizing the codon usage of Escherichia coli (E. coli). The expression of the recombinant protein was confirmed via SDS-PAGE and Western blot technique. Results: The residues 41-160 of IpaD, 21-89 of StxB, and 40-335 of TolC were selected. According to half-life, instability, and buried indices, IpaD-StxB-TolC was selected as the best arrangement. The Ramachandran plot showed that 97.077% of the amino acids were in the favored area. Linear and conformational epitopes were also present throughout the chimeric protein sequence. Moreover, the C-ImmSim server indicated that IgG and IgM titers could reach desirable values by the third injection. Furthermore, the stability of the mRNA-optimized gene was enhanced, increasing the Codon Adaptive Index (CAI) to 0.9. Finally, the chimeric gene was transferred to E. coli BL21, and the expression of the 60.6 kDa recombinant protein was confirmed. Conclusion: The results indicated that the recombinant protein could act as a proper immunogen candidate against Shigella spp.