Exploiting sulfur transfer machinery in Mycobacterium tuberculosis: Discovery of novel CysA2-directed antitubercular leads.

The emergence of multidrug-resistant (MDR) and extensively drug-resistant (XDR) Mycobacterium tuberculosis strains highlights the requirement for new therapeutic targets and antitubercular chemotypes. CysA2, a sulfur transferase that participates in sulfur metabolism and redox homeostasis, is a relatively underexplored therapeutic target. Here we used an integrated computational approach to discover potential small molecule inhibitors of CysA2. This led to prioritization of 448 candidates for MM-GBSA rescoring from the > 448,000 compounds screened, where the binding free energies ranged from -68.57 to -14.10 kcal/mol, compared to -16.25 kcal/mol for the reference ligand S-nitrosoglutathione (GSNO). The best candidates were F0808-0813, F1631-0176 and F2532-0240 with MM-GBSA binding energies of -68.57, -62.98 and -61.46 kcal/mol, respectively. Further 500 ns molecular dynamics simulations showed particularly favorable dynamic behavior for F0808-0813 and F2532-0240, while F1631-0176 displayed comparatively higher ligand mobility and conformational variability. F2532-0240 displayed the most favorable overall dynamic profile, including stable conformational sampling and the lowest superimposition RMSD (0.771 Å) of the investigated systems. The DFT analysis further confirmed the electronic stability of F0808-0813 and F2532-0240, with HOMO-LUMO gaps of 4.517 and 4.000 eV, respectively, versus 3.025 eV for GSNO. QM/MM analysis further supported accommodation of prioritized ligands in the binding environment of CysA2. Taken together, the results point to F2532-0240 and F0808-0813 as the top CysA2-directed candidates for further experimental validation and structure-guided anti-tubercular drug development.