Pneumococcal conjugate vaccines (PCVs) were constructed through chemical conjugation of pneumococcal capsules to immunogenic carrier proteins. The PCVs implementation in developing countries was prevented by their high manufacturing costs. This issue can be overcome by development of protein based vaccines against pneumococci. Antibody responses are necessary for protection against S. pneumoniae. Autolysin, zinc binding lipoprotein (ZBL), and plasmid stabilization protein (PSP) were already identified as pneumococcal surface proteins able to elicit protection against S. pneumoniae serotype 19F and their most probable immunoprotective B-cell epitope regions (MIBRs) were determined. MIBRs were fully conserved in the most common pneumococcal serotypes causing invasive pneumococcal disease in children. Whole antigens are not as potent as epitope based vaccines and every epitope in a multi epitope based vaccine can individually induce a protective immune response against the pathogen. Thus better immunoprotection can be achieved by multi epitope based vaccines. In the present study, therefore, we aim to design a chimerical vaccine against pneumococci based on the identified MIBRs using immunoinformatic tools. These regions were joined together using the (EAAAK) ₄ linker. The MIBRs orders affected the immunoprotective ability of the fusion protein as estimated by VaxiJen tool. The fusion protein consisting of MIBRs of autolysin, PSP and ZBL respectively (APZ) showed the highest probability for eliciting immunoprotection and was used for further study. The codon optimization was done for APZ using OPTIMIZER. Analysis of the mRNA secondary structure using Mfold tool revealed no stable hairpin at the 5' end and thus the antigen can be expressed appropriately. The 3D model of the antigen resulted from I-TASSER indicated the presence of alpha helix, turn, and coil as the protein structural elements. Analyzing physicochemical properties of the chimerical antigen using ProtParam showed that the fusion protein was stable and its half life in Escherichia coli was more than 10 h. Considering the GRAVY score, the chimerical antigen possessed a hydrophilic nature and it can be expressed in the soluble form in E. coli at 92.2% probability. These results demonstrated that the chimerical antigen composed of conserved MIBRs is a suitable vaccine candidate, which can elicit protection against common pneumococcal serotypes.

computational design, pneumococcal conjugate vaccines, protective epitope, protein based vaccines, Streptococcus pneumoniae