Brucellosis, caused by the genus Brucella bacterium, is a well-known infection among domestic animals. Considering the serious economic and medical consequences of this infection, various preventive efforts have been made through using recombinant vaccines, based on outer membrane protein (OMP) antigens of Brucella species. The objective of the present study was to clone, analyze the sequence, and predict the epitopes of Omp31 gene as a major B. melitensis antigen. The full-length open reading frame (ORF) for this gene was amplified by specific primers and cloned into the pTZ57R/T vector. The gene sequence of B. melitensis Rev 1 strain was submitted to NCBI database. The results of phylogenetic analysis showed that Omp31 is almost similar in different Brucella species. Online prediction software programs were also used to predict B- and Tcell epitopes, secondary and tertiary structures, antigenicity, and enzymatic degradation sites. The bioinformatic tools in the current study were confirmed by the results of three different experimental epitope prediction studies. Bioinformatic analysis identified one T-cell and three B-cell epitopes for Omp31 antigen. Finally, based on the antigenicity and proteosome recognition sites, common B- and T-cell epitopes were predicted for Omp31 (amino acids 191-204). Bioinformatic analysis showed that these regions had proper epitope characterization and could be useful for recombinant vaccine development

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