title: A de novo designed 2[4Fe-4S] ferredoxin mimic mediates electron transfer.
abstract: [Fe-S] clusters, nature's modular electron transfer units, are often arranged in chains that support long-range electron transfer. Despite considerable interest, the design of biomimetic artificial systems emulating multicluster-binding proteins, with the final goal of integrating them in man-made oxidoreductases, remains elusive. Here, we report a novel bis-[4Fe-4S] cluster binding protein, DSD-Fdm, in which the two clusters are positioned within a distance of 12 Å, compatible with the electronic coupling necessary for efficient electron transfer. The design exploits the structural repeat of coiled coils as well as the symmetry of the starting scaffold, a homodimeric helical protein (DSD). In total, eight hydrophobic residues in the core of DSD were replaced by eight cysteine residues that serve as ligands to the [4Fe-4S] clusters. Incorporation of two [4Fe-4S] clusters proceeds with high yield. The two [4Fe-4S] clusters are located in the hydrophobic core of the helical bundle as characterized by various biophysical techniques. The secondary structure of the apo and holo proteins is conserved; further, the incorporation of clusters results in stabilization of the protein with respect to chemical denaturation. Most importantly, this de novo designed protein can mimic the function of natural ferredoxins: we show here that reduced DSD-Fdm transfers electrons to cytochrome c, thus generating the reduced cyt c stoichiometrically.
authors.affiliation: Department of Chemistry and Biochemistry, Arizona State University , Tempe, Arizona 85287-1604, United States.
authors.forename: Anindya
authors.initials: A
authors.lastname: Roy
authors.forename: Dayn Joseph
authors.initials: DJ
authors.lastname: Sommer
authors.forename: Robert Arthur
authors.initials: RA
authors.lastname: Schmitz
authors.forename: Chelsea Lynn
authors.initials: CL
authors.lastname: Brown
authors.forename: Devens
authors.initials: D
authors.lastname: Gust
authors.forename: Andrei
authors.initials: A
authors.lastname: Astashkin
authors.forename: Giovanna
authors.initials: G
authors.lastname: Ghirlanda
mesh_terms: D004579:Electron Transport; D005288:Ferredoxins / Q000138:chemical synthesis / Q000737:chemistry*; D008958:Models, Molecular; D011487:Protein Conformation; D055550:Protein Stability
chemical_list: D005288:Ferredoxins