Solid-state electron transport via cytochrome c depends on electronic coupling to electrodes and across the protein.
Electronic coupling to electrodes, Γ, as well as that across the examined molecules, H, is critical for solid-state electron transport (ETp) across proteins. Assessing the importance of each of these couplings helps to understand the mechanism of electron flow across molecules. We provide here experimental evidence for the importance of both couplings for solid-state ETp across the electron-mediating protein cytochrome c (CytC), measured in a monolayer configuration. Currents via CytC are temperature-independent between 30 and ∼130 K, consistent with tunneling by superexchange, and thermally activated at higher temperatures, ascribed to steady-state hopping. Covalent protein-electrode binding significantly increases Γ, as currents across CytC mutants, bound covalently to the electrode via a cysteine thiolate, are higher than those through electrostatically adsorbed CytC. Covalent binding also reduces the thermal activation energy, Ea, of the ETp by more than a factor of two. The importance of H was examined by using a series of seven CytC mutants with cysteine residues at different surface positions, yielding distinct electrode-protein(-heme) orientations and separation distances. We find that, in general, mutants with electrode-proximal heme have lower Ea values (from high-temperature data) and higher conductance at low temperatures (in the temperature-independent regime) than those with a distal heme. We conclude that ETp across these mutants depends on the distance between the heme group and the top or bottom electrode, rather than on the total separation distance between electrodes (protein width).
Departments of Materials and Interfaces, Organic Chemistry, and Immunology, Weizmann Institute of Science, Rehovot 76305, Israel.
Nadav
N
Amdursky
Doron
D
Ferber
Carlo Augusto
CA
Bortolotti
Dmitry A
DA
Dolgikh
Rita V
RV
Chertkova
Israel
I
Pecht
Mordechai
M
Sheves
David
D
Cahen
D000818:Animals; D045304:Cytochromes c / Q000235:genetics / Q000378:metabolism*; D004553:Electric Conductivity; D004566:Electrodes; D004579:Electron Transport / Q000502:physiology*; D004926:Escherichia coli; D006418:Heme / Q000378:metabolism; D006736:Horses; D016297:Mutagenesis, Site-Directed; D009154:Mutation / Q000235:genetics; D011485:Protein Binding; D013696:Temperature
D006418:Heme; D045304:Cytochromes c
bioelectronics; protein conduction; temperature dependence