en Original article Original article <p> <strong> Introduction: </strong>Omp31 is animmunodominant and protective antigen conserved in <i>Brucella</i> species and a good candidate for vaccine design. <strong>Material & methods:</strong> The present study aimed at <i>in silico</i> design of the truncated Omp31 (TOmp31) using bioinformatic tools and to express the selected form in <i>Escherichia coli (E. coli</i>) <strong>Results and conclusion:</strong> Various bioinformatically calculated scores for the model showed that the structure conformation of the truncated Omp31 is in the range of the native protein with the C-score, Z-score, TM-score and Ramachandran Z-score of the truncated form model being -0.53, -0.72 and -0.98 respectively. Amplification of TOmp31 produced a single fragment of approximately 345 bp which was cloned in the pET28a expression vector. The integrity of the constructed vector (pET28- TOmp31) was confirmed by PCR and restriction digestion analysis and the rTOmp31 was successfully expressed in <i>E. coli</i> BL21. SDS-PAGE analysis of the lysate from the induced <i>E. coli</i> carrying the TOmp31 construct and the purified protein showed the expected molecular mass of approximately 12 kDa. The yield of the purified protein was estimated at approximately 250 μg/ml. Anti-His antibody reacted with the purified protein in Western blot confirming its expression in the prokaryotic system. Future studies exploring the immunogenicity and cross-protection of the protein against <i>Brucella spp.</i> are underway. <i>Vac Res</i> <i>, 2014, 1 (1): 16-21</i></p> Brucella, Omp31, Modeling, Truncated, In silico analysis 16 20 http://vacres.pasteur.ac.ir/browse.php?a_code=A-10-27-7&slc_lang=en&sid=1 Maryam Golshani No Departmant of Molecular Biology, Pasteur Institute of Iran, Tehran, Iran Payam Zandi No Departmant of Molecular Biology, Pasteur Institute of Iran, Tehran, Iran Saeid Bouzari saeidbouzari@yahoo.com Yes Departmant of Molecular Biology, Pasteur Institute of Iran, Tehran, Iran