A new twist of rubredoxin function in M. tuberculosis

Electron transfer mediated by metalloproteins drives many biological processes. Rubredoxins are ubiquitous iron-containing electron carriers that play important roles in bacterial adaptation to changing environmental conditions. In Mycobacterium tuberculosis, oxidative and acidic stresses as well as iron starvation induce rubredoxin expression. However, their functions during M. tuberculosis infection is unknown. In the present work, we show that rubredoxin B (RubB) supports catalytic activity of mycobacterial cytochrome P450s, CYP124, CYP125, and CYP142, which are important for bacterial viability and pathogenicity. We solved the crystal structure of RubB and characterized the interaction between RubB and CYPs using site-directed mutagenesis. Mutations that neutralized single charge on the surface of RubB did not dramatically decrease activity of studied CYPs, and isothermal calorimetry (ITC) experiments indicated that interactions are transient and not highly specific. Our findings suggest that a switch from ferredoxins to rubredoxins support CYP activity in M. tuberculosis-infected macrophages. Our electrochemical experiments suggest potential applications of RubB in biotechnology.