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

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.