Engineering a Recombinant Chimeric Protein Consisting of OmpL Antigen Conjugated to HBHA Molecular Adjuvant (HBHA-OmpL) with the Aim of Developing a Vaccine Against Salmonella Typhimurium

Salmonella Typhimurium is a zoonotic gram-negative bacterium of the Enterobacteriaceae family. One of the newest ways against the pathogen is the use of recombinant vaccines. In this study, a recombinant construct consisting of OmpL antigen from Salmonella Typhimurium and HBHA protein as a molecular adjuvant from Mycobacterium was designed by an in silico method and a peptide linker. For this purpose, sequences of these proteins were extracted from the database and the HBHA-OmpL recombinant construct was designed based on the correct  reading frame. Then, reliable online servers were used to evaluate the immunogenicity score and  physicochemical properties as well as the secondary and tertiary structures of the designed construct. The best refined 3D model was used for the molecular docking process. A codon optimization was done for expression in E. coli, and the possible cloning  of the optimized nucleotide sequence in pET22b(+) expression vector was evaluated. Based on the results obtained in this study, the HBHA-OmpL chimeric construct with a molecular weight of 49.45 kDa had an instability index of 32.75 and an antigenicity index of 0.688, and alpha helices and random coil structures had the largest contribution in its secondary structure. The protein-protein docking results showed that despite being conjugated with OmpL protein, HBHA molecule was able to connect to TLR4/MD2 receptor by 23 hydrogen bonds. Also, cloning results confirmed that nucleotide sequence of the designed vaccine can be successfully inserted in pET22b(+) vector.