Novel Chimeric Vaccine Candidate Development against Leptotrichia buccalis

Abstract

The misuse of antibiotics in our daily lives has led to the emergence of antimicrobial resistance. As a result, many antibiotics are becoming ineffective. This phenomenon is linked with high rates of mortality and morbidity. Therefore, new approaches are required to address this major health issue. Leptotrichia buccalis is a Gram-negative, rod-shaped bacterium which normally resides in the oral and vaginal cavities. It is an emerging bacterial pathogen which is developing new antibiotic-resistance mechanisms. No approved vaccine is available against this pathogen, which is a cause for growing concern. In this study, an in silico-based, multi-epitopes vaccine against this pathogen was designed by applying reverse vaccinology and immunoinformatic approaches. Of a total of 2193 predicted proteins, 294 were found to be redundant while 1899 were non-redundant. Among the non-redundant proteins, 6 were predicted to be present in the extracellular region, 12 in the periplasmic region and 23 in the outer-membrane region. Three proteins (trypsin-like peptidase domain-containing protein, sel1 repeat family protein and TrbI/VirB10 family protein) were predicted to be virulent and potential subunit vaccine targets. In the epitopes prediction phase, the three proteins were subjected to B- and T-cell epitope mapping; 19 epitopes were used for vaccine design. The vaccine construct was docked with MHC-I, MHC-II and TLR-4 immune receptors and only the top-ranked complex (based on global energy value) was selected in each case. The selected docked complexes were examined in a molecular dynamic simulation and binding free energies analysis in order to assess their intermolecular stability. It was observed that the vaccine binding mode with receptors was stable and that the system presented stable dynamics. The net binding free energy of complexes was in the range of -300 to -500 kcal/mol, indicating the formation of stable complexes. In conclusion, the data reported herein might help vaccinologists to formulate a chimeric vaccine against the aforementioned target pathogen.

Keywords: Leptotrichia buccalis; molecular docking; molecular dynamics simulation; multi-epitopes vaccine.

Figure 1

Schematic diagram of a multi-epitope vaccine construct. The blue colored box represents the adjuvant, EAAAK is indicated in black text, epitopes are shown in yellow and GPGPG linkers are shown in orange.

Figure 2

Disulfide engineering of the designed chimeric vaccine. (A) Wild-type structure of the vaccine construct. (B) Mutated structure of the vaccine construct. Mutated amino acid residues are shown in yellow.

Figure 3

Docked complex of vaccine and MHC-I molecule (A), MHC-II molecule (B) and TLR-4 (C). The vaccine is shown in yellow while MHC-I, MHC-II and TLR-4 are shown in light blue, medium blue and orange, respectively.

Figure 4

Analysis of simulation trajectories using RMSD (A), RMSF (B) and (C) hydrogen bonds.