This subproject is one of many research subprojects utilizing theresources provided by a Center grant funded by NIH/NCRR. The subproject andinvestigator (PI) may have received primary funding from another NIH source,and thus could be represented in other CRISP entries. The institution listed isfor the Center, which is not necessarily the institution for the investigator.We propose to measure the Fe K-edge Extended X-ray Absorption Fine Structure (EXAFS) of various ferric complexes of siderophores bound by the human protein siderocalin. Siderophores are iron chelating agents secreted by microorganisms to solubilize ferric iron and mediate iron uptake. Recently, siderocalin, a human protein, has been proposed as an antibacterial component of the immune system because it binds the ferric complex of enterobactin (FeEnt) and therefore acts as a growth inhibitor of E. coli. The binding of ferric complexes by siderocalin is the first indication that proteins may be produced to bind siderophores as an immune response to bacterial infection. Understanding the coordination chemistry of the ferric complexes of enterobactin and siderophore analogs as a function of pH and protein environment is therefore important for understanding microbial iron transport and the immune systems response to pathogen growth. EXAFS spectroscopy can provide important structural characterization of the local iron(III) environment in ferric complexes formed with enterobactin or synthetic analogs inside the protein calix.
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