Iron Mineralizing Bacterioferritin A from Mycobacterium tuberculosis Exhibits Unique Catalase-Dps-like Dual Activities

Mycobacterium tuberculosis ( Mtb) expresses heme binding protein nanocages, bacterioferritin A (BfrA), along with nonheme bacterioferritin B (BfrB). BfrA is unique to bacteria and, like BfrB, carries out ferroxidase activity to synthesize iron oxide biominerals. The expression of BfrA, in the presence of BfrB, indicates that Mtb may utilize it for some additional purpose apart from its natural iron storage activity. However, the mechanism of ferroxidase activity (iron biomineralization) in Mtb BfrA still remains unexplored. H 2 O 2 is secreted by the host during host-pathogen interaction. In some bacteria, heme containing Bfr and/or Dps (DNA binding protein during starvation) detoxify H 2 O 2 by utilizing it during their ferroxidase activity. Interestingly, Mtb lacks the gene for Dps which protects DNA from H 2 O 2 -induced oxidative cleavage. Therefore, the current work investigates the kinetics of O 2 /H 2 O 2 -dependent ferroxidase activity, DNA protection, and catalase-like activity of recombinant Mtb BfrA. Ferroxidase activity by Mtb BfrA was found to proceed via the formation of a transient intermediate and its initial rate exhibited sigmoidal behavior, with increasing Fe 2+ concentration. Moreover, Mtb BfrA exhibited catalase-like activity by evolving O 2 upon reaction with H 2 O 2 , which gets inhibited in the presence of catalase inhibitors (NaN 3 and NaCN). In addition, Mtb BfrA protected plasmid DNA from Fenton reagents (Fe 2+ and H 2 O 2 ), similar to Dps, by forming BfrA-DNA complexes. Thereby, Mtb BfrA executes multiple functions (ferroxidase, catalase, and Dps-like activities) in order to cope with the host generated oxidative stress and to promote pathogenesis.