Background:S. dysenteriae is the causative agent of shigellosis, a severe form of bacillary
dysentery and this infectious disease is still a health problem worldwide, especially in children. The most
important proteins of the Shigella type III secretion system are IpaB and IpaD, which attach to the
intestinal epithelial cells and provide the possibility of invasion and disease. These two proteins with
immunogenic properties can be a suitable target to design and manufacture subunit recombinant vaccines.
Objective: The aim of this study is to design an immunogenic chimeric protein against IpaB and IpaD
as a subunit vaccine candidate through an in silico study.
Methods: Firstly, the immunogenic epitopes of amino acid sequences, physico-chemical parameters,
and the allergenicity of the chimeric protein were determined. Then the tertiary structure and the
potential ability of the chimeric protein were predicted and evaluated in terms of inducing B cells’
immune responses with effective epitopes. Finally, the optimization of the chimeric protein was
examined as the index affecting the protein expression.
Results: Data showed an instability index of 37.18 and a well-established predicted third structure for
the chimeric protein, with a z-score of -6.11. Also, more than 99% of its amino acids were in the
optimal range. Minimum energy for mRNA structure increased to -317.9 and the Codon Adaptive
Index (CAI) rose to 88%. The designed protein had no IgE specific B cell epitopes.
Conclusion: Overall, the results of this study show that the designed protein can be considered as an
immunogen vaccine candidate against S. dysenteriae.