Proteome Exploration of Legionella pneumophila for Identifying Novel Therapuetics: A Hierarchical Subtractive Genomics and Reverse Vaccinology Approach

Legionella pneumophila, the causative agent of a serious type of pneumonia (lung infection) called Legionnaires disease. It is emerging as an antibacterial resistant strain day by day. Hence, the identification of novel drug targets and vaccine candidates is essential to fight against this pathogen. Herein attempts were taken through subtractive genomics approach on complete proteome of L. pneumophila to address the challenges of multidrug resistance. A total 2930 proteins from L. pneumophila proteome were investigated through diverse subtractive proteomics approaches, e.g., identification of human non-homologous and pathogen-specific essential proteins, druggability and anti-target analysis, prediction of subcellular localization, human microbiome non-homology screening, protein-protein interactions studies in order to find out effective drug and vaccine targets. Only 3 were identified that fulfilled all these criteria and proposed as novel drug targets against L. pneumophila. Furthermore, outer membrane protein TolB was identified as potential vaccine target with better antigenicity score and allowed for further in silico analysis to design a unique multiepitope subunit vaccine against it. Antigenicity and transmembrane topology screening, allergenicity and toxicity assessment, population coverage analysis, and molecular docking approach were adopted to generate the most potent epitopes. The final vaccine was constructed by the combination of highly immunogenic epitopes along with suitable adjuvant and linkers. The designed vaccine construct showed higher binding interaction with different MHC molecules and human immune TLR2 receptors with minimum deformability at molecular level. The translational potency and microbial expression of the vaccine protein was also analyzed using pET28a(+) vector. The present study aids in the development of novel therapeutics and vaccine candidates for efficient treatment of the infections caused by Legionella pneumophila. However, further wet lab-based investigations and in vivo trials are highly recommended to experimentally validate our prediction.