title: Incorporating electron-transfer functionality into synthetic metalloproteins from the bottom-up.
abstract: The alpha-helical coiled-coil motif serves as a robust scaffold for incorporating electron-transfer (ET) functionality into synthetic metalloproteins. These structures consist of a supercoiling of two or more aplha helices that are formed by the self-assembly of individual polypeptide chains whose sequences contain a repeating pattern of hydrophobic and hydrophilic residues. Early work from our group attached abiotic Ru-based redox sites to the most surface-exposed positions of two stranded coiled-coils and used electron-pulse radiolysis to study both intra- and intermolecular ET reactions in these systems. Later work used smaller metallopeptides to investigate the effects of conformational gating within electrostatic peptide-protein complexes. We have recently designed the C16C19-GGY peptide, which contains Cys residues located at both the "a" and "d" positions of its third heptad repeat in order to construct a nativelike metal-binding domain within its hydrophobic core. It was shown that the binding of both Cd(II) and Cu(I) ions induces the peptide to undergo a conformational change from a disordered random coil to a metal-bridged coiled-coil. However, whereas the Cd(II)-protein exists as a two-stranded coiled-coil, the Cu(I) derivative exists as a four-stranded coiled-coil. Upon the incorporation of other metal ions, metal-bridged peptide dimers, tetramers, and hexamers are formed. The Cu(I)-protein is of particular interest because it exhibits a long-lived (microsecond) room-temperature luminescence at 600 nm. The luminophore in this protein is thought to be a multinuclear CuI4Cys4(N/O)4 cage complex, which can be quenched by exogenous electron acceptors in solution, as shown by emission-lifetime and transient-absorption experiments. It is anticipated that further investigation into these systems will contribute to the expanding effort of bioinorganic chemists to prepare new kinds of functionally active synthetic metalloproteins.
authors.affiliation: Department of Chemistry and Center for Photochemical Sciences, Bowling Green State University, Bowling Green, Ohio 43403, USA.
authors.forename: Jing
authors.initials: J
authors.lastname: Hong
authors.forename: Olesya A
authors.initials: OA
authors.lastname: Kharenko
authors.forename: Michael Y
authors.initials: MY
authors.lastname: Ogawa
mesh_terms: D000595:Amino Acid Sequence; D001665:Binding Sites; D002104:Cadmium / Q000737:chemistry; D003198:Computer Simulation; D003300:Copper / Q000737:chemistry; D003545:Cysteine / Q000737:chemistry / Q000378:metabolism; D019281:Dimerization; D004579:Electron Transport / Q000502:physiology*; D057927:Hydrophobic and Hydrophilic Interactions; D008667:Metalloproteins / Q000737:chemistry* / Q000378:metabolism; D008670:Metals / Q000737:chemistry*; D008969:Molecular Sequence Data; D010084:Oxidation-Reduction; D010455:Peptides / Q000737:chemistry* / Q000378:metabolism; D017433:Protein Structure, Secondary; D012428:Ruthenium / Q000737:chemistry; D055672:Static Electricity; D013997:Time Factors; D014783:Viscosity
chemical_list: D008667:Metalloproteins; D008670:Metals; D010455:Peptides; D002104:Cadmium; D003300:Copper; D012428:Ruthenium; D003545:Cysteine