XAS STUDIES ON HEME PROTEINS

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This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. Primary support for the subproject and the subproject's principal investigator may have been provided by other sources, including other NIH sources. The Total Cost listed for the subproject likely represents the estimated amount of Center infrastructure utilized by the subproject, not direct funding provided by the NCRR grant to the subproject or subproject staff. Heme proteins have been studied extensively by x-ray absorption spectroscopy, but new proteins/roles continue to emerge. XANES and multiple-scattering XAFS studies are sensitive probes of their oxidation state, coordination number and the nature of the coordinating ligands. We will study the heme structures with respect to the roles of neuroglobin (Nb) in the brain, NO binding and other functions of myoglobin (Mb) in cardiovascular disease, and the new protein, indoleamine 2,3-dioxygenase-2 (IDO-2), in the kidneys. We will use these techniques to compare the structures of different adducts and oxidation states of the isolated proteins with those contained within cells. In particular, whether Nb confers neuro-protection during cerebral ischemia is controversial and we plan to study changes in the structures of intracellular neuroglobin in neurons under normal conditions and those associated with stroke and neurodegenerative diseases. Similarly, NO binding to Mb is important in the health of the cardiovascular system, but it is uncertain as to whether it binds to the thiolate group, the heme centre or both in human Mb in vivo. We will compare the XAS data from isolated proteins with those found in cells under various conditions associated with normal conditions and those associated with cardiovascular disease. Finally, the recently discovered IDO-2 metabolizes tryptophan, like the well-studied IDO (now known as IDO-1). However, IDO-2, unlike IDO-1, loses its activity when the protein is isolated and purified. XAS will be used to study the structural changes that occur during the isolation procedures in order to ascertain the likely active structure in vivo. This is important as there is mounting evidence that IDO-2 in the kidney has a role in controlling blood pressure and, hence, understanding the nature of the active form and how its activity may be modulated to control blood pressure has many potential applications in the treatment of both low and high blood pressure.