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Background & objective: Diphtheria, caused by toxigenic strains of Corynebacterium diphtheria is a fatal disease that was characterized by Hippocrates in 5 B.C. Exotoxin (dTX) is causative agent of this lethal disease. Diphtheria toxin consist two chains, catalytic (A) and binding (B) chain. The toxin binds to its receptor by binding chain (B) and enters in many of body cells such as myocardial, kidney and peripheral nerve cells. After entering, catalytic chain (A) inhibits protein synthesis and cause target cell death. Currently, toxoid form of diphtheria toxin used as vaccine. The aim of this study was design and provide of synthetic mutated catalytic subunit of diphtheria toxin. Then, regarding to its bioinformatics study, this gene would cloned and expressed as recombinant protein vaccine. Methods: After determining and optimizing of dtx gene sequence containing two mutations (A158G, G52E), and perform its bioinformatics study, this synthetic gene was provided in expression vector and molecular analysis was carried out. The pET28a/dtxA construct was transformed in Bl21DE3 E.coli. Then, recombinant protein expression and production as a vaccine candidate was evaluated by western blotting technique. Results: Regarding to the codon optimization of A subunit of diphtheria toxin and bioinformatics analysis, the synthetic mutated gene in expression vector was ordered and provided. The molecular analysis of this gene by restriction digestion and electrophoresis was confirmed its accuracy. This protein was confirmed by western blotting after expression and production. Conclusion: According to advantages of DtxA recombinant protein to diphtheria toxoid, it seems this recombinant protein, as vaccine candidate, could be replaced with diphtheria vaccine. This issue should been completed by more researches.

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Introduction: Heat labile toxin (LT) is one of the virulence factors of Enterotoxigenic Escherichia coli. B subunit of LT (LHB) is the binding subunit and can induce six months immunity in humans. Tetanus toxin of Clostridium Tetani causes the fatal disease, tetanus. This toxoid induces two years immunity in humans. Hc subunit, as binding domain of the toxoid is considered as immunogenic part of tetanus toxin. The THc and LTB recombinant subunits have the potential role to induce immunological memories with different longevity. The purpose of this study was to evaluate and compare the immunogenicity of THc and LTB recombinant proteins in animal model and also to evaluate their roles in immunity duration. Materials & methods: The recombinant proteins, THc and LTB, were expressed in the transgenic host, E.Coli Bl21 DE3 using pET28a vector containing their respected genes in optimum condition. After express-ion, LTB and THc were purified from insoluble and soluble phases, respectively. Then, their purity was confirmed by SDS-PAGE gel. To evaluate their immuno-genicity, these proteins were injected into mice and the antibody titer were evaluated and compared by ELISA technique. Findings: SDS-PAGE results showed overexpressed levels of the proteins under study.Immunity assessment revealed that in the same condition of immunity the THc subunit produces a higher antibody titer in comparison with the LTB subunit. ِDiscussion & Conclusion: The first step in creating a strong and long-lasting immune-ological memory is the induction of high titer of antibody. Thus, the difference in antibody titer may be related to memory cells lifetime in the immunized mice.