Mycobacteria Have A System For Acquiring Iron From Heme …

The tuberculosis-causing microorganism, Mycobacterium tuberculosis, has a system for acquiring iron from free heme and hemoglobin, molecular biologists have discovered (Proc. Natl. Acad. Sci. USA, DOI: 10.1073/pnas.1009516108). This system could provide a new target for tuberculosis therapeutics. Until recently, M. tuberculosis, which usually gets its iron by using molecules called siderophores to remove the metal from the human proteins transferrin and lactoferrin, seemed unable to use the more abundant iron bound by heme and hemoglobin. But Celia W. Goulding of the University of California, Irvine, and coworkers have now found and characterized a mycobacterial heme acquisition system. Using affinity chromatography, the researchers captured the heme-binding protein Rv0203. They solved the crystal structure of the protein, which is a dimer of dimers. Each monomer consists of five α-helices, and the dimers form a cagelike structure with a hydrophobic core. The key residues in the heme-binding site are two histidines and a tyrosine. In addition, Goulding and coworkers identified two putative transmembrane heme transporters in the microorganism.