Integrated genomic, immunoinformatic and experimental evaluation of conserved pneumococcal surface proteins for serotype-independent vaccine development
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Published on: April 5, 2019
Sangeetha Gopalakrishnan1,2, Premkumar Jayapal3,4, Prathibha Selvamani1
1Department of Medical Laboratory Technology, School of Allied Health Science, Sathyabama Institute of Science and Technology, Chennai, India.
Background:
Pneumococcal conjugate vaccines (PCVs), which target capsular polysaccharides, have significantly reduced the burden of invasive pneumococcal disease; however, their effectiveness is limited by serotype replacement, geographic variation, and the emergence of non-vaccine serotypes.
Methods:
Pan-genome analysis was conducted to identify the conserved core genes of S. pneumoniae. An integrated bioinformatics approach, incorporating PSORTb, SignalP, TMHMM, and domain-based motif analysis, predicted Surface-associated proteins. Highly conserved Surface-associated proteins were further evaluated for their gene expression in vitro infection of A549 lung epithelial cells using RT-qPCR, and surface accessibility assessment by flow cytometry. Further immunoinformatics analyses for their antigenicity (VaxiJen), linear B-cell epitope prediction (BepiPred 3.0), and MHC-II (HLA-DR) binding prediction was perfoemd.
Results:
Four surface-associated lipoproteins-PsaA, AdcA, AmiA, and Lmb-were universally conserved and predicted to be surface-exposed. During epithelial cell infection, all four genes were actively expressed, with psaA showed greater early upregulation (~ 2.5-fold; p < 0.05). Flow cytometry confirmed surface localization of all proteins, with PsaA exhibiting the highest accessibility (92% positive cells; highest MFI). Immunoinformatics analyses demonstrated strong antigenicity scores, enriched linear B-cell epitope clusters, and multiple high-affinity MHC-II binding peptides for these proteins, particularly PsaA and AdcA. In contrast, conserved multi-pass transmembrane proteins (e.g., SecG, MisCA, EcfT) showed limited surface accessibility.
Conclusions:
The study identifies conserved pneumococcal surface proteins that could be used as a vaccine candidate. PsaA is the most promising serotype-independent vaccine candidate, while other AdcA, AmiA, and Lmb represent potential antigens for multicomponent formulations.
