STRUCTURAL CHARACTERIZATION OF METAL TRANSPORTING PEPTIDES FROM MAMMALS & MICROO

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This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Iron uptake in gram negative bacteria is accomplished through the use of siderophores (small modified peptides). Siderophores scavenge iron from the external environment and are then transported back into the bacterial cell. Siderophores complexed to toxic metals have been shown to be an effective antibacterial strategy. We will use the collected XAFS data to relate metal-binding properties, and structural changes. We will also use the high resolution XAFS data of the metal-binding sites to further refine our X-ray crystal structure data, which will be solved in parallel with these experiments. Iron uptake in humans is being investigated by the small peptide, gastrin17, which functions in the gastric lumen at acidic pH. Gastrin17 has been shown to bind two Fe-atoms, and although no structural data has yet been collected, evidence suggests these irons are bound as a dinuclear iron species. XAFS data will not only provide the first structural picture of the iron-binding site, but may also provide evidence of how closely the metals are bound with respect to one another. It has recently been postulated that the prion protein, involved in a range of deleterious neurological diseases, may function as a copper-sensing or copper-transporting protein at the synapse in mammals. Copper-binding has been linked to the formation of the disease state of the protein, although atomic resolution structural data is sparse. X-ray crystallography is of little use as the copper-binding region is highly unstructured in solution, as well as the solid state. Also, due to the paramagnetic nature of copper (Cu2+) NMR techniques are unable to probe the region immediately around the metal centre. We are therefore screening other metal ions with favourable NMR properties, using the XAFS technique to compare with the Cu2+-binding environment.