title: Copper Environment in Artificial Metalloproteins Probed by Electron Paramagnetic Resonance Spectroscopy.
abstract: 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.
authors.affiliation: Department of Chemistry and Biochemistry, Arizona State University , Tempe, Arizona 85287-1604, United States.
authors.forename: Marco
authors.initials: M
authors.lastname: Flores
authors.affiliation: Department of Chemistry and Biochemistry, Arizona State University , Tempe, Arizona 85287-1604, United States.
authors.forename: Tien L
authors.initials: TL
authors.lastname: Olson
authors.affiliation: Department of Chemistry and Biochemistry, Arizona State University , Tempe, Arizona 85287-1604, United States.
authors.forename: Dong
authors.initials: D
authors.lastname: Wang
authors.affiliation: Department of Chemistry and Biochemistry, Arizona State University , Tempe, Arizona 85287-1604, United States.
authors.forename: Selvakumar
authors.initials: S
authors.lastname: Edwardraja
authors.affiliation: Department of Chemistry and Biochemistry, Arizona State University , Tempe, Arizona 85287-1604, United States.
authors.forename: Sandip
authors.initials: S
authors.lastname: Shinde
authors.affiliation: Department of Chemistry and Biochemistry, Arizona State University , Tempe, Arizona 85287-1604, United States.
authors.forename: JoAnn C
authors.initials: JC
authors.lastname: Williams
authors.affiliation: Department of Chemistry and Biochemistry, Arizona State University , Tempe, Arizona 85287-1604, United States.
authors.forename: Giovanna
authors.initials: G
authors.lastname: Ghirlanda
authors.affiliation: Department of Chemistry and Biochemistry, Arizona State University , Tempe, Arizona 85287-1604, United States.
authors.forename: James P
authors.initials: JP
authors.lastname: Allen
mesh_terms: D001665:Binding Sites; D002264:Carboxylic Acids / Q000737:chemistry; D003300:Copper / Q000737:chemistry*; D004578:Electron Spin Resonance Spectroscopy; D006863:Hydrogen-Ion Concentration; D007093:Imidazoles / Q000737:chemistry; D008024:Ligands; D008667:Metalloproteins / Q000737:chemistry*; D008958:Models, Molecular
chemical_list: D002264:Carboxylic Acids; D007093:Imidazoles; D008024:Ligands; D008667:Metalloproteins; D003300:Copper