Background
Streptococcus pneumoniae (Pneumococcus)
has remained a leading cause of fatal infections such as pneumonia,
meningitis, and sepsis. Moreover, this pathogen plays a major role in
bacterial co-infection in patients with life-threatening respiratory
virus diseases such as influenza and COVID-19. High morbidity and
mortality in over one million cases, especially in very young children
and the elderly, are the main motivations for pneumococcal vaccine
development. Due to the limitations of the currently marketed
polysaccharide-based vaccines, non-serotype-specific protein-based
vaccines have received wide research interest in recent years. One step
further is to identify high antigenic regions within multiple
highly-conserved proteins in order to develop peptide vaccines that can
affect various stages of pneumococcal infection, providing broader
serotype coverage and more effective protection. In this study,
immunoinformatics tools were used to design an effective multi-epitope
vaccine in order to elicit neutralizing antibodies against multiple
strains of pneumococcus.
Results
The
B- and T-cell epitopes from highly protective antigens PspA (clades
1–5) and PhtD were predicted and immunodominant peptides were linked to
each other with proper linkers. The domain 4 of Ply, as a potential TLR4
agonist adjuvant candidate, was attached to the end of the construct to
enhance the immunogenicity of the epitope vaccine. The evaluation of
the physicochemical and immunological properties showed that the final
construct was stable, soluble, antigenic, and non-allergenic.
Furthermore, the protein was found to be acidic and hydrophilic in
nature. The protein 3D-structure was built and refined, and the
Ramachandran plot, ProSA–web, ERRAT, and Verify3D validated the quality
of the final model. Molecular docking analysis showed that the designed
construct via Ply domain 4 had a strong interaction with TLR4. The
structural stability of the docked complex was confirmed by molecular
dynamics. Finally, codon optimization was performed for gene expression
in E. coli, followed by in silico cloning in the pET28a(+) vector.
Conclusion
The
computational analysis of the construct showed acceptable results,
however, the suggested vaccine needs to be experimentally verified in
laboratory to ensure its safety and immunogenicity.