Orientation-Dependent Electron Transport in a Single Redox Protein

• Published in: ACS nano Vol. 6; no. 1; pp. 355 - 361
• Main Authors: Della Pia, Eduardo Antonio, Elliott, Martin, Jones, D. Dafydd, Macdonald, J. Emyr
• Format: Journal Article
• Language: English
• Published: United States American Chemical Society 24.01.2012
• Subjects: Conductance; Contact; Cytochromes; Cytochromes b - chemistry; Cytochromes b - genetics; Cytochromes b - ultrastructure; Electric contacts; Electron transfer; Electron Transport; Gold; Mutation; Nanostructure; Oxidation-Reduction; Protein Binding; Protein Conformation; Protein Engineering - methods; Proteins; Thiols; cytochrome b 562; protein engineering; molecular electronics; scanning tunneling microscopy; nanobioelectronics; single-molecule conductance
• ISSN: 1936-0851; 1936-086X
• DOI: 10.1021/nn2036818

The redox-active protein cytochrome b 562 has been engineered to introduce pairs of thiol groups in the form of cysteine residues at specified sites. Successful STM imaging of the molecules adsorbed on a gold surface indicated that one thiol group controls the orientation of the molecule and that the protein maintains its native form under the experimental conditions. Stable protein–gold STM tip electrical contact was directly observed to form via the second free thiol group in current–voltage and current–distance measurements. Proteins with thiol contacts positioned across the protein’s short axis displayed a conductance of (3.48 ± 0.05) × 10–5 G 0. However proteins with thiol groups placed along the long axis reproducibly yielded two distinct values of (1.95 ± 0.03) × 10–5 G 0 and (3.57 ± 0.11) × 10–5 G 0, suggesting that the placement of the asymmetrically located haem within the protein influences electron transfer. In contrast, the unengineered wild-type cytochrome b 562 had conductance values at least 1 order of magnitude less. Here we show that an electron transfer protein engineered to bind gold surfaces can be controllably oriented and electrically contacted to metallic electrodes, a prerequisite for potential integration into electronic circuits.