Superfund Research Program

Toxic Metal Interactions With Cellular Proteins

Project Leader: Dean E. Wilcox
Grant Number: P42ES007373
Funding Period: 2000-2008

Project-Specific Links

Final Progress Reports

Year:   2007  2004 

The goal of this project is to quantify the molecular and structural effects of toxic metals (arsenic, mercury, lead, cadmium, nickel and chromium) on proteins that are functionally compromised by the toxic metal.  This research focuses primarily on certain target proteins, such as the DNA-binding domain of glucocorticoid receptor (GR), which has been shown in Project 2 to be a site for arsenic and chromium effects in vivo, and the DNA-binding domain of the transcription factor Sp1, which is involved in the expression of a variety of genes.  These proteins have natural binding sites for zinc (so-called zinc fingers), which are also putative binding sites for toxic metals, and Dr. Wilcox and his research team are continuing to quantify the affinity and thermodynamics of zinc and toxic metals binding to these sites.  However, basic chemical information about the interaction of toxic metals with sulfur-containing thiol ligands, such as those found at these and other protein binding sites, is often lacking.  Thus, the researchers have studied arsenic (As) and mercury (Hg) binding to simple biologically-relevant thiol ligands to provide the chemical background for understanding their interaction with thiols in target proteins.  Since these two metals have inorganic and organic forms that are biologically important, both forms have been studied.  The research team has now quantified the stability of arsenite (As(III)) and monomethylarsenite (MMA) complexes with the sulfur-containing tri-peptide glutathione (GSH), which is found in all cells and against which all cellular protein binding sites must compete for arsenic.  They have also shown that conformational flexibility can significantly lower the stability of As-thiol complexes, thereby implicating protein sites with rigid juxtaposition of two thiols as sites with higher affinity for arsenic.  They have determined that the higher toxicity of MMA may have a fundamental chemical basis – the greater strength of its As-S bonds.  Finally, they have shown that organic forms of mercury have a lower affinity for thiol ligands and weaker Hg-S bonds than does the inorganic mercuric ion, Hg(II).