Central to the understanding of metal protein interactions has been the question of whether metals enforce specific quarternary structure in proteins or whether proteins impart a specific coordination environment on the metal. Several amphiphilic, a-helical peptides have been designed de novo in order to permit a direct experimental determination of the factors which define metal protein interactions. By placing cysteine residues into the interior of the bundle to generate metal binding sites, we can test directly the stability of a particular bundle and the role of metal-ion coordination geometry in altering this stability. We have chosen a series of thiophilic metals that have coordination preferences including 2 coordinate (linear), 3 coordinate (trigonal) and 4 coordinate (tetrahedral) to deduce the thermodynamic stabilities associated with metal binding in these different environments. The metals to be studied are Zn(II), Hg(II), Cd(II), Cu(I), Ag(I) and Co(II). With the exception of the Co(II), which serves as a control, there is no technique other than EXAFS that can provide unambigous characterization of the local metal-site structure.
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