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

Abstract

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. H2O2 is secreted by the host during host-pathogen interaction. In some bacteria, heme containing Bfr and/or Dps (DNA binding protein during starvation) detoxify H2O2 by utilizing it during their ferroxidase activity. Interestingly, Mtb lacks the gene for Dps which protects DNA from H2O2-induced oxidative cleavage. Therefore, the current work investigates the kinetics of O2/H2O2-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 Fe2+ concentration. Moreover, Mtb BfrA exhibited catalase-like activity by evolving O2 upon reaction with H2O2, which gets inhibited in the presence of catalase inhibitors (NaN3 and NaCN). In addition, Mtb BfrA protected plasmid DNA from Fenton reagents (Fe2+ and H2O2), 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.