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Copper Environment in Artificial Metalloproteins Probed by Electron Paramagnetic Resonance Spectroscopy B
- Flores, Marco, Olson, Tien L., Wang, Dong, Edwardraja, Selvakumar, Shinde, Sandip, Williams, JoAnn C., Ghirlanda, Giovanna, Allen, James P.
- The Journal of physical chemistry 2015 v.119 no.43 pp. 13825-13833
- amino acids, binding sites, circular dichroism spectroscopy, copper, divalent metals, electron paramagnetic resonance spectroscopy, ligands, metalloproteins, pH, peptides, spectral analysis
- The design of binding sites for divalent metals in artificial proteins is a productive platform for examining the characteristics of metal–ligand interactions. In this report, we investigate the spectroscopic properties of small peptides and four-helix bundles that bind Cu(II). Three small peptides, consisting of 15 amino acid residues, were designed to have two arms, each containing a metal-binding site comprised of different combinations of imidazole and carboxylate side chains. Two four-helix bundles each had a binding site for a central dinuclear metal cofactor, with one design incorporating additional potential metal ligands at two identical sites. The small peptides displayed pH-dependent, metal-induced changes in the circular dichroism spectra, consistent with large changes in the secondary structure upon metal binding, while the spectra of the four-helix bundles showed a predominant α-helix content but only small structural changes upon metal binding. Electron paramagnetic resonance spectra were measured at X-band revealing classic Cu(II) axial patterns with hyperfine coupling peaks for the small peptides and four-helix bundles exhibiting a range of values that were related to the specific chemical natures of the ligands. The variety of electronic structures allow us to define the distinctive environment of each metal-binding site in these artificial systems, including the designed additional binding sites in one of the four-helix bundles.