EPR and NMR spectroscopies provide input on the coordination of Cu(I) and Ag(I) to a disordered methionine segment

Abstract

Methionine motifs are methionine-rich metal-binding segments found in many human, yeast, and bacterial proteins involved in the transportation of copper ion to other cellular pathways, and in protecting copper from oxidation. Methionine motifs are found to bind Ag(I) and Cu(I) ions. Proteins or peptides that can bind different metal ions should have the ability to differentiate between them, to be able to shuttle them to various pathways in the cell. This study utilizes electron paramagnetic resonance spectroscopy together with circular dichroism and nuclear magnetic resonance to probe structural changes in the methionine segment upon coordinating Cu(I) and Ag(I) metal ions. The data collected here indicate that methionine segments experience structural changes while coordinating Cu(I) and Ag(I), however, the differences between the coordination of Cu(I) vs. Ag(I) to the methionine segment are mild. Since Cu(I) and Ag(I) metal ions are pretty similar in their nature and charge, the minor structural changes reported here are significant towards the understanding of the differences in the transport mechanism of these two metal ions in prokaryotic and eukaryotic cells.

Insights into the N-terminal Cu(II) and Cu(I) binding sites of the human copper transporter CTR1

“…The broadening of the signal suggests that the two termini of each peptide get closer to each other upon Cu(I) binding. The decrease in the hyperfine value following Cu(I) introduction, a phenomenon that we have observed previously for other segments containing Met [60], suggests that, upon Cu(I) coordination, the spin-labels shift to point to a somewhat more hydrophobic environment. the a N value varies slightly across the different peptide variants, suggesting that each substitution has a slight effect on the folding of the peptide.…”

The Advantages of EPR Spectroscopy in Exploring Diamagnetic Metal Ion Binding and Transfer Mechanisms in Biological Systems

“…The binding of diamagnetic metal ions, such as Zn(II), Mg(II), Cu(I) and Ag(I), to proteins, has been mostly studied by nuclear magnetic resonance (NMR) and X-ray absorbance fine structure (EXAFS) spectroscopy, techniques that can provide information on the metal coordination site at the molecular level, specifically those atoms and residues involved in metal binding [12][13][14][15][16]. While electron paramagnetic resonance (EPR) spectroscopy cannot provide information on residues directly involved in the coordination of diamagnetic metal ions, it can, however, probe the dynamics and conformational changes in a biomolecule in solution upon metal ion binding, thereby providing important structural and functional information on the biomolecule as a function of metal coordination.…”

Metallo-vesicular catalysis: A mixture of vesicular cysteine/iron mediates oxidative pH switchable catalysis

“…interaction of the Fe 3+ /cysteine complex with the SDS head groups, which decreases the electrostatic interactions between the oppositely charged heads. The asymmetric S=O band is sensitive to changes in the types of neighboring head groups, and the obvious change in shape of the spectrum resulted from changes in the microenvironment [28,33,34,50]. The splitting of this band results from electrostatic interactions of Fe 3+ /cysteine with SDS, perhaps via the ammonium side chain.…”