A multi-subunit based, thermodynamically stable model vaccine using combined immunoinformatics and protein structure based approach.

Immunizations with the conventional vaccines have failed to effectively inhibit the incidences and further dissemination of the infections. To address it, we have implemented protein structure based strategies to design an efficient multi-epitope subunit vaccine against Mycobacterium avium subsp. paratuberculosis (MAP). Previously reported immunodominant peptide epitope sequences from MAP1611 protein were conjugated together with a stretch of conserved amino acid residues of heparin-binding hemagglutinin, reported as a TLR4 agonist and was employed as an adjuvant to polarize the cellular responses toward host protective Th1 responses. These three types of component peptides were combined with the help of relevant linkers for efficient separation to improve and intensify the antigen processing and presentation. The primary structures of these multi peptides were 3-dimensional homology modeled to yield the final chimeric vaccine. Further, its conformational correctness and stability enhancement was assessed using molecular dynamics (MD) simulations. Finally, disulfide engineering in the most flexible regions of the molecule yielded three potential mutants, Y593C-E610C, Q631C-A634C and a double mutant Q631C-A634C/Y593C-E610C. The double mutant represents thermodynamically most stable version among them. It is potentially highly antigenic, soluble and non-allergen molecule interacting with the TLR receptor expressed on the immune cells. This vaccine contains both T-cell and several B-cell epitopes and an adjuvant which potentially possess protective cellular and humoral immune responses triggering properties. The presented vaccine strategy will be proven a promising pathogen specific candidate with wide therapeutic application against MAP which may be extended to other prevalent infections in future.