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.

背景：痢疾链球菌是志贺菌病（一种严重的细菌性痢疾）的病原体，这种传染病仍然是全世界的健康问题，尤其是在儿童中。志贺氏菌III型分泌系统中最重要的蛋白质是IpaB和​​IpaD，它们附着在肠上皮细胞上并提供了侵袭和疾病的可能性。具有免疫原性的这两种蛋白质可以是设计和生产亚单位重组疫苗的合适靶标。

目的：本研究的目的是通过计算机研究设计一种针对作为亚基疫苗候选物的IpaB和​​IpaD的免疫原性嵌合蛋白。

方法：首先，测定氨基酸序列的免疫原性表位，理化参数和嵌合蛋白的致敏性。然后，通过诱导具有有效表位的B细胞的免疫反应，来预测和评估嵌合蛋白的三级结构和潜在能力。最后，将嵌合蛋白的最优化作为影响蛋白表达的指标进行检查。

结果：数据显示不稳定性指数为37.18，并且嵌合蛋白的公认的预测第三结构的z值为-6.11。而且，其99％以上的氨基酸都在最佳范围内。mRNA结构的最小能量增加到-317.9，密码子适应指数（CAI）上升到88％。设计的蛋白质没有IgE特异性B细胞表位。

结论：总体而言，这项研究的结果表明，设计的蛋白质可以被认为是针对痢疾链球菌的免疫原疫苗候选。