Publications

The transduction of odorant binding into cellular signaling by olfactory receptors (ORs) is not understood and knowing its mechanism would enable developing new pharmacology and biohybrid electronic detectors of volatile organic compounds bearing high sensitivity and selectivity. The electrical characterization of ORs in bulk experiments is subject to microscopic models and assumptions. We have directly determined the nanoscale electrical properties of ORs immobilized in a fixed orientation, and their change upon odorant binding, using electrochemical scanning tunneling microscopy (EC-STM) in near-physiological conditions. Recordings of current versus time, distance, and electrochemical potential allows determining the OR impedance parameters and their dependence with odorant binding. Our results allow validating OR structural-electrostatic models and their functional activation processes, and anticipating a novel macroscopic biosensor based on ORs.Copyright © 2022 The Authors. Published by Elsevier B.V. All rights reserved.

JTD Keywords: electrochemical scanning tunneling, electrochemical scanning tunneling microscopy (ec-stm), microscopy (ec-stm), neurons, odorant binding, olfactory receptors (ors), open-circuit voltage(voc), Olfactory receptors (ors), Open-circuit voltage (v(oc)), Transport

Charge separation and transport through the reaction center of photosystem I (PSI) is an essential part of the photosynthetic electron transport chain. A strategy is developed to immobilize and orient PSI complexes on gold electrodes allowing to probe the complex's electron acceptor side, the chlorophyll special pair P700. Electrochemical scanning tunneling microscopy (ECSTM) imaging and current-distance spectroscopy of single protein complex shows lateral size in agreement with its known dimensions, and a PSI apparent height that depends on the probe potential revealing a gating effect in protein conductance. In current-distance spectroscopy, it is observed that the distance-decay constant of the current between PSI and the ECSTM probe depends on the sample and probe electrode potentials. The longest charge exchange distance (lowest distance-decay constant ?) is observed at sample potential 0 mV/SSC (SSC: reference electrode silver/silver chloride) and probe potential 400 mV/SSC. These potentials correspond to hole injection into an electronic state that is available in the absence of illumination. It is proposed that a pair of tryptophan residues located at the interface between P700 and the solution and known to support the hydrophobic recognition of the PSI redox partner plastocyanin, may have an additional role as hole exchange mediator in charge transport through PSI.© 2021 Wiley-VCH GmbH.

JTD Keywords: azurin, current distance decay spectroscopy, cytochrome c(6), electrochemical scanning tunneling microscopy (ecstm), electrochemistry, photosystem i, photosystem-i, plastocyanin, protein electron transfer, recognition, single metalloprotein, single molecules, structural basis, tunneling spectroscopy, 'current, Amino acids, Charge transfer, Chlorine compounds, Current distance decay spectroscopy, Decay spectroscopies, Distance decay, Electrochemical scanning tunneling microscopy, Electrochemical scanning tunneling microscopy (ecstm), Electrodes, Electron transfer, Electron transport properties, Gold compounds, Photosystem i, Photosystems, Protein electron transfer, Protein electron-transfer, Proteins, Scanning tunneling microscopy, Silver halides, Single molecule, Single molecules

We present a method to measure directly and at the single-molecule level the distance decay constant that characterizes the rate of electron transfer (ET) in redox proteins. Using an electrochemical tunneling microscope under bipotentiostatic control, we obtained current-distance spectroscopic recordings of individual redox proteins confined within a nanometric tunneling gap at a well-defined molecular orientation. The tunneling current decays exponentially, and the corresponding decay constant (β) strongly supports a two-step tunneling ET mechanism. Statistical analysis of decay constant measurements reveals differences between the reduced and oxidized states that may be relevant to the control of ET rates in enzymes and biological electron transport chains.

JTD Keywords: Long-range electron transfer (LRET), Distance decay constant, Single-molecule electrochemistry, Redox enzyme, Metalloprotein, Blue copper protein, Azurin, Electrochemical scanning tunneling microscopy and spectroscopy, Nanoelectrodes, Debye length, Electrochemical charge screening