Heme transport and utilization in shigella dysenteriae angela wilks

Pathogenic bacteria require iron for their survival and growth, and the ability to acquire this element is in part linked to their virulence. Some obligate pathogens such as N. meningitidis, S. dysenteriae and H, influenzae have evolved sophisticated mechanisms for iron acquisition that directly utilize the hosts heme-containing proteins. The mechanism of iron release and the fate of the porphyrin macrocycle are not known. The utilization of heme by pathogenic bacteria involves at least six proteins of which none have been studied at the biochemical level. I recently expressed and purified to homogeneity a 37 kDa protein (SHU37) from S. dysenteriae. SHU37 has high sequence identity with the product of the hems gene of Y. entercolitica, the product of which was proposed to be a heme oxygenase. The amino acid sequence of HemS shows no homology with heme oxygenase. The SHU37 protein has been investigated for both its heme binding and oxygenase activity. The ligation state of the heme, lack of oxygenase activity and localization to the periplasm suggests the protein may be a periplasmic binding protein. SHU37 functions to transport heme across the periplasmic space to the cytoplasmic permease/ATPase complex, where it may function as a soluble receptor for the complex.