Rv1899c, an HDAC1–ZBTB25-Interacting Protein of Mycobacterium tuberculosis, Promotes Stress Resistance and Immune Evasion in Infected Macrophages

Rv1899c, a previously identified HDAC1-ZBTB25-interacting protein of <i>Mycobacterium tuberculosis</i>, plays a crucial role in bacterial adaptation and immune modulation. Recombinant <i>M. smegmatis</i>-expressing <i>Rv1899c</i> (MS_ <i>Rv1899c</i>) showed enhanced survival under acidic and oxidative stress compared to vector controls, along with improved early intracellular growth in THP1-derived macrophages. This was accompanied by reduced reactive oxygen species (ROS), diminished cytokines associated with inflammation and downregulation of autophagy proteins ATG5, Beclin, and LC3, which ultimately skewed the immune response, suppressing the pro-inflammatory M1 macrophage population. Targeting Rv1899c with 3-aminobenzamide (3-AB) impaired intracellular bacterial survival and restored IL-12B expression, while its combination with the HDAC inhibitor C1994 significantly enhanced bacterial clearance. Structural modelling confirmed the high stereochemical quality of the Rv1899c macrodomain, and computational studies identified 3-AB as the strongest ligand (-5.75 kcal/mol), stabilized through hydrogen bonding and hydrophobic interactions with key residues. Molecular dynamics simulations conducted for 200 ns demonstrated stable protein-ligand interactions with consistent parameters, while MM/GBSA analysis indicated favourable binding energy (ΔG_bind = -6.6 kcal/mol), largely influenced by van der Waals and electrostatic forces. Together, these findings highlight <i>Rv1899c</i> as a mediator of stress resistance and immune evasion and propose it as a potential therapeutic target against <i>M. tuberculosis</i>.