Identification of B-cell Epitope Regions in Cell Surface Proteins of Streptococcus pneumoniae Serotype 19F Using Bioinformatic Tools

Abstract

Pneumococcal conjugate vaccines (PCVs) were developed through chemical coupling of polysaccharide capsules of pneumococci to immunogenic carrier proteins and World Health Organization recommends inclusion of these vaccines in national immunization programs for children. However, the PCVs implementation in developing countries is prevented by the high vaccine manufacturing costs. This issue can be resolved by construction of protein based vaccines against pneumococci. We already identified three pneumococcal surface proteins including autolysin, zinc binding lipoprotein (ZBL), and plasmid stabilization protein (PSP) as appropriate protein candidates for eliciting protection against S. pneumoniae serotype 19F. The protein protective antigenicity and the absence of autoimmunity induction were used as selection criteria. However, regarding the necessity of the antibody response for protection against pneumococci, analysis of protective B-cell epitopes of these proteins is required to elucidate their usefulness in new vaccine formulations. In the present study, therefore, we aim to identify protective B-cell epitope regions of these proteins via widely used bioinformatic tools. Both of the Bepipred and BCPreds programs were used for identification of linear B-cell epitopes. The conformational B-cell epitopes were predicted using the CBTope program. The immunoprotective abilities of epitopes were evaluated using VaxiJen. We determined the linear B-cell epitope regions, which were predicted by both Bepipred and BCPreds and have common amino acids with conformational B-cell epitopes. Our results showed that all of the three studied proteins included such protective overlapped linear B-cell epitope regions. However, a truncated form of PSP had the greatest number of the protective overlapped B-cell epitope regions.Moreover, the most probable protective epitope region resides in this protein and this epitope region is completely conserved in PSPs of serotype 19F pneumococcal strains. Therefore, the truncated PSP was an appropriate candidate for development of protein based vaccines against S. pneumoniae serotype 19F.