Abstract
| - The synthetic peptide encompassing residues 106−126 (PrP106−126, KTNMKHMAGAAAAGAVVGGLG) of the human prion protein was considered for its binding properties toward copper(II),manganese(II) and zinc(II) at pH 5.7. 1H and 13C 1D spectra, 1H spin−lattice relaxation rates, and 1H−15Nand 1H−13C HSQC 2D experiments were obtained in the absence and in the presence of metal ions. WhileZn(II) was found to yield negligible effects upon any NMR parameter, metal−peptide association wasdemonstrated by the paramagnetic effects of Cu(II) and Mn(II) upon 1D and 2D spectra. Delineation ofstructures of metal complexes was sought by interpreting the paramagnetic effect on 1H spin−latticerelaxation rates. Exchange of peptide molecules from the metal coordination sphere was shown to providesizable contribution to the observed relaxation rates. Such contribution was calculated in the case of Cu(II); whereas the faster paramagnetic rates of peptide molecules bound to Mn(II) were determining spin−lattice relaxation rates almost exclusively dominated by exchange. Proton−metal distances were thereforeevaluated in the case of the Cu(II) complex only and used as restraints in molecular dynamics calculationswherefrom the structure of the complex was obtained. The peptide was shown to bind copper through theimidazole nitrogen and the ionized amide nitrogen of His-111 and the amino-terminal group with the terminalcarboxyl stabilizing the coordination sphere through ionic interactions. The data were interpreted as todemonstrate that the hydrophobic C-terminal region was not affecting the copper-binding properties of thepeptide and that this hydrophobic tail is left free to interact with other target molecules. As for the complexwith Mn(II), qualitative information was obtained on carbonyl oxygens of Gly-124 and Leu-125, beyond theterminal Gly-126 carboxyl, being at close distance from the metal ion, that also interacts, most likely, througha hydrogen bond of metal-bound water, with the imidazole ring of His-111.
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