Heavy metal poisoning by elements such as mercury, lead, cadmium, and arsenic is a significant human health problem. Understanding the interaction of heavy metals with proteins is essential for defining the mechanism of toxicity, developing ways to minimize human exposure and to provide therapeutic regimens for the removal of toxic ions. Our goals are (1) to develop peptide systems that provide a foundation for understanding metal binding by metalloregulatory proteins and metallochaperones, (2) to understand the thermodynamics and kinetics of heavy metals in helical assemblies and (3) to prepare new designed peptides utilizing different ligands (e.g., histidine or D-amino acids) or asymmetric binding sites in single polypeptides that fold into 1-helical bundles. To achieve these goals we will use a de novo peptide system based on the three-stranded coiled coil peptide aggregate motif that encapsulates with high affinity single heavy metal ions and provides spectroscopic models of mercury, cadmium, and arsenic binding sites in biological systems. We will generate high resolution structures of this peptide system in the presence and absence of these heavy metals, elucidate the kinetic and thermodynamic mechanisms of heavy metal encapsulation, and expand the array of characterized systems to include single chain peptides that encapsulate heavy metals, coiled coils that provide different coordination environments than the original design and those that encapsulate more than one heavy metal ion. These studies will expand the foundation of knowledge that has been laid by the scientific community investigating metallopeptide design, metalloregulatory proteins and heavy metal detoxification. These objectives will develop insight into the interplay between metal coordination and apopeptide structure in defining the overall metallopeptide fold, an important aspect of metallopeptide design.
Relevance to Human Health Heavy metals such as PbII, HgII, AsII and CdII cause severe health concerns due both to their acute toxicity and the long term effects of chronic exposure (e.g., the EPA estimated in 2002 that over 300,000 children in the USA had blood levels exceeding 10 ?g/dL). Our studies address these concerns in numerous ways: including making mimics of heavy metal binding sites in proteins in order to understand how heavy metals bind to proteins, defining the rates at which reactions occur and establishing the thermodynamic preferences of these metals to different sites. We are also relating this work to studies on proteins used to recognize or detoxify heavy metals in bacteria, fungi and humans (e.g., assessing how HgII interacts with the human copper chaperone HAH1).
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