Design and in silico evaluation of a novel chimeric protein vaccine candidate against Salmonella Typhi.

Typhoid fever, caused by Salmonella enteritidis serovar Typhi (S. Typhi), remains a significant global health challenge, especially in regions with poor sanitation. Despite available vaccines, limitations such as short-term efficacy and variable immune responses necessitate novel strategies. Here, we designed a multi-protein chimeric protein vaccine targeting S. Typhi by integrating three key antigens: SteD (an immune-evasion transmembrane effector) (whole protein), flagellin (D1 domain), and STIV (Salmonella Typhi invasion protein) (whole protein). Proteins were linked via rigid EAAAK linkers to enhance stability. The construct exhibited high antigenicity (VaxiJen score:0. 9228) and favorable physicochemical properties (ProtParam), with non-allergenic (AlgPred) and non-toxic (ToxinPred) profiles. Structural analysis revealed a stable 3D model (I-TASSER/Phyre2/RaptorX), validated by Ramachandran plot (>90 % favored regions), ProSA z-score of -5.54, and ERRAT. B-cell and T-cell epitopes predicted by IEDB, ABCPred, and Discotope 2.0 demonstrated strong binding to HLA alleles. Molecular docking confirmed robust interactions with TLR-4 (PDB:2Z63) and TLR-5 (PDB:3V44), while 100-ns MD simulations (NAMD/VMD) affirmed complex stability (low RMSD/RMSF). Immune simulations (C-ImmSim) predicted potent humoral and cellular responses, including elevated IgG/IgM and Th1/Th2 cytokines. This in silico study proposes a promising vaccine candidate with high theoretical immunogenicity and structural integrity, warranting further in vitro and in vivo validation.