King's College London

• Design and test a single-protein electronics platform that allows electrical characterisation of individual redox proteins under oriented magnetic/electric force fields.
• Electrical transduction of redox enzymatic catalysis in a single enzyme.
• Mapping the effect of magnetic and electric fields in the single-enzyme activity.

Protein production and purification, Protein mutagenesis, biophysical characterisation, electrode surface modification and characterisation, electric circuits engineering, nanoscale electrical charcterisation and single-olecule electronics.

Techniques: surface IR, UV-vis, MassSpec, circular dichroism, Electrochemistry, atomic force and scanning tunnelling microscopies, electron microscopies.

The progress of this ERC project so far is summarised below:

• We have set up three independent scanning probe-based microscopes with capabilities to create and electrically characterise individual proteins trapped in a nanoscale gap between two conductive electrodes. Among the special features of such equipment, it operates under ambient conditions using a liquid cell to work at (near) physiological conditions, allows temperature and electrochemical control of the cell, and allows the easy implementation of high electric and magnetic force fields along the main nanogap axis.
• We have characterised the main electrical signatures of metalloporphyrins and alpha-helical peptide sequences, which are the main constituents of the redox enzyme studied in this ERC, namely, Cytochrome P450, Small Tetraheme Cytochromes and Ferritin. Main results show: (1) the conductivity of supramolecularly trapped metalloporphyrin is governed by the chemical details of the interactions. (2) There exist particular electron pathways in the metalloporphyrin moiety promoting spin polarisation of the currents. (3) An alpha-helical peptide structure bearing large electrical dipole running through the maim helical axis can control the sign of the spin polarisation of the electrons crossing the helical structure.
• We have shown electrical transduction of enzymatic catalysis in a single enzyme trapped in a nanoscale junction. The study allowed the comparison of the slow P450 with a fast Glutathione Reductase enzymes.
• We have demonstrated quantum-supported conductivity in a small tetraheme cytochrome protein, which links to the observed long-range charge transport observed in multiheme based molecular wires in electrical bacteria. The work has been now extended to a longer decaheme cytochrome system which corroborates the long-range charge transport model proposed for these protein complexes.
• We have concluded our studies of the understanding of the Fe release mechanism in a Ferritin protein under an electrical perturbation. We have identified a passive (non-catalysed) mechanism for the Fe release.
• In partnership with ETH Zurich, we have translated the electrostatic catalysis concept exploited by enzymes to two synthetic device platforms; a microfluidic device, and a piezoelectric material’s surface.

Our initial measurements on redox cofactors and alpha-helical peptides (WP1) have brought unprecedented electrical behaviours in these molecular moieties which are constituent parts of cytochrome enzymes (Angewandte Chemie, ACS, and ChemistryViews). The main block (WP2) has produced new surface preparation protocols to effectively trap enzymes in a nanoscale junction. Single-protein electrical characterisation using our controlled protein trapping in a nanoscale gap has revealed outstanding electrical behaviour in the studied enzymes:

1. We have been able to compare the electrical response of two different enzymes individually trapped in a nanoscale junction, namely, P450 and Glutathione Reductase, and electrically characterise their distinct enzymatic activity at the single-enzyme level.
2. We have characterised quantum-supported charge transport in a multiheme protein and demonstrated the role of the redox heme cofactor in catalysing this process and leading to long-range charge transport behaviour.
3. We have established plausible mechanisms for the electrochemically induced Fe release in a Ferritin enzyme, and connect such mechanisms to the Ferritin biological functions as well as the possible avenues for new methods of electrochemical sensing of ferritin in blood serum.
4. We have demonstrated biology-inspired electrostatic catalysis in two different technological platforms, namely, a microfluidic channel and a piezoelectric material. The work has generated a number of high-impact publications (JACS, Nature Communications, Chemical Science, etc).