Mimicking Protein−Protein Electron Transfer:  Voltammetry ofPseudomonas aeruginosaAzurin and theThermus thermophilusCuADomain at ω-Derivatized Self-Assembled-Monolayer Gold Electrodes

Fujita, Kyoko; Nakamura, Nobufumi; Ohno, Hiroyuki; Leigh, Brian S.; Niki, Katsumi; Gray, Harry B.; Richards, John H.

doi:10.1021/ja047875o

Cited by 122 publications

(156 citation statements)

References 59 publications

(112 reference statements)

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“…With mercaptoundecanoic acid, in contrast, the anodic and cathodic signals were no longer observed, suggesting a larger decrease in the ET. These results are consistent with previous studies on mitochondrial cyt c [7,9,17] as well as other small soluble proteins [61,62], which showed an almost distance-independent measured rate for short-length thiols (C1-C10) and an exponential decrease of the ET rate for longer ones. We also note that the width of the peaks is larger for the proteins immobilized on mercaptohexanoic acid than on mercaptopropionic acid.…”

Section: Cyclic Voltammetrysupporting

confidence: 93%

Electrochemical study of an electron shuttle diheme protein: The cytochrome c from T. thermophilus

Melin

Schoepp‐Cothenet²,

Abdulkarim³

et al. 2017

Inorganica Chimica Acta

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ABSTRACT:Cytochrome c550, a diheme protein from the thermophilic bacterium Thermus thermophilus, is involved in an alternative respiration pathway allowing the detoxification of sulfite ions. It transfers the two electrons released from the oxidation of sulfite in a sulfite:cytochrome c oxidoreductase (SOR) enzyme to heme/copper oxidases via the monoheme cytochrome c552. It consists of two conformationally independent and structurally different domains (the C-and Nterminal) connected by a flexible linker. Both domains harbor one heme moiety. We report here the redox properties of the full-length protein and the individual C-and N-terminal fragments.We show by UV/Vis and EPR potentiometric titrations that the two fragments exhibit very similar potentials, despite their different environments. In the full-length protein, however, the N-terminal heme is easier to reduce than the C-terminal one, due to cooperative interactions.This finding is consistent with the kinetic measurements which showed that the N-terminal domain only accepts electrons from the SOR. Cytochrome c552 is able to interact with its partners both through electrostatic and hydrophobic interactions as could be shown by measuring efficient electron transfer at gold electrodes modified with charged and hydrophobic groups, respectively. The coupling of electrochemistry with infrared spectroscopy allowed us to monitor the conformational changes induced by electron transfer to each heme separately and to both simultaneously.

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Section: Cyclic Voltammetrysupporting

confidence: 93%

Electrochemical study of an electron shuttle diheme protein: The cytochrome c from T. thermophilus

Melin

Schoepp‐Cothenet²,

Abdulkarim³

et al. 2017

Inorganica Chimica Acta

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“…Trp48 is nestled in a hydrophobic pocket of the protein and thought to be important in long-range charge transfer in azurin [185]. In further studies, Trp48 has proven necessary for redox activity in azurin mutants [186] and shows significant fluorescence quenching in the presence of copper [187], further demonstrating the profound effect of protonation state on tryptophan-mediated charge transfer. The properties of indoles and their capacity to engage in both concerted and stepwise PCET afford these species great flexibility as electron-shuttle residues in redoxactive proteins; model systems allow for close examination of the subtleties pertinent to both concerted and stepwise PCET pathways and their consequences.…”

Section: Indolesmentioning

confidence: 87%

Proton-Coupled Electron Transfer in Organic Synthesis: Fundamentals, Applications, and Opportunities

Miller

Tarantino

Knowles

2016

Topics in Current Chemistry Collections

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Proton-coupled electron transfers (PCETs) are unconventional redox processes in which both protons and electrons are exchanged, often in a concerted elementary step. While PCET is now recognized to play a central a role in biological redox catalysis and inorganic energy conversion technologies, its applications in organic synthesis are only beginning to be explored. In this chapter we aim to highlight the origins, development and evolution of PCET processes most relevant to applications in organic synthesis. Particular emphasis is given to the ability of PCET to serve as a non-classical mechanism for homolytic bond activation that is complimentary to more traditional hydrogen atom transfer processes, enabling the direct generation of valuable organic radical intermediates directly from their native functional group precursors under comparatively mild catalytic conditions. The synthetically advantageous features of PCET reactivity are described in detail, along with examples from the literature describing the PCET activation of common organic functional groups.

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“…1A shows a schematic representation in which the hydrophobic patch around the copper center in azurin is spatially and chemically suitable for coupling to the terminal methyl group of the alkanethiol. Mutagenesis experiments showed that the mutation of the tryptophan 48 (Trp 48) to other residues in azurin results in complete quenching of interfacial ET (38). Trp 48, which is not supposed to interact physically with the methyl group of the alkanethiol, thus appears still to play an important role in establishing the electronic coupling of azurin to the electrode surface (38).…”

Section: Methodsmentioning

confidence: 99%

“…Mutagenesis experiments showed that the mutation of the tryptophan 48 (Trp 48) to other residues in azurin results in complete quenching of interfacial ET (38). Trp 48, which is not supposed to interact physically with the methyl group of the alkanethiol, thus appears still to play an important role in establishing the electronic coupling of azurin to the electrode surface (38). The wild-type protein molecules are confined well by hydrophobic interactions to form a monolayer with the copper center facing the electrode surface (Fig.…”

Section: Methodsmentioning

confidence: 99%

“…An interfacial ET rate constant of Ϸ30 s Ϫ1 was observed, largely consistent with intramolecular ET between the copper center and the Cys 3 Cys 26 site measured by pulse radiolysis in homogeneous solution (44 s Ϫ1 ) (29). Interfacial ET can be significantly facilitated by wiring azurin molecules onto the gold surface by variable-length alkanethiols through noncovalent interactions of the hydrophobic patch around the copper ion with the terminal methyl group (37,38). In this work, we use azurin as an example for comprehensive observations of long-range interfacial ET properties and particularly for in situ mapping of redox-gated tunneling resonance at the single-molecule level.…”

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confidence: 99%

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Long-range protein electron transfer observed at the single-molecule level: In situ mapping of redox-gated tunneling resonance

Chi

Farver

Ulstrup

2005

Proc. Natl. Acad. Sci. U.S.A.

173

220

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A biomimetic long-range electron transfer (ET) system consisting of the blue copper protein azurin, a tunneling barrier bridge, and a gold single-crystal electrode was designed on the basis of molecular wiring self-assembly principles. This system is sufficiently stable and sensitive in a quasi-biological environment, suitable for detailed observations of long-range protein interfacial ET at the nanoscale and single-molecule levels. Because azurin is located at clearly identifiable fixed sites in well controlled orientation, the ET configuration parallels biological ET. The ET is nonadiabatic, and the rate constants display tunneling features with distance-decay factors of 0.83 and 0.91 Å ؊1 in H2O and D2O, respectively. Redoxgated tunneling resonance is observed in situ at the single-molecule level by using electrochemical scanning tunneling microscopy, exhibiting an asymmetric dependence on the redox potential. Maximum resonance appears around the equilibrium redox potential of azurin with an on͞off current ratio of Ϸ9. Simulation analyses, based on a two-step interfacial ET model for the scanning tunneling microscopy redox process, were performed and provide quantitative information for rational understanding of the ET mechanism.blue copper protein ͉ scanning tunneling microscopy ͉ nanoscale bioelectronics ͉ bioelectrochemistry C harge transfer plays key roles in many chemical and biological processes as well as in molecular electronics (1-5). For example, long-range protein electron transfer (ET) is central in aerobic respiration and photosynthesis. The importance of longrange ET is illustrated by a recent special issue of PNAS on this topic (6-12). Several articles reflect broadly the current status of this subject. However, one of the major objectives in nanoscale science and technology is to fabricate molecular electronic devices with specified functions. Molecular electronics is rooted in the concept of molecular charge transfer (particularly, molecular conductivity) (13,14). Two essential steps involved in bottom-up manipulations are (i) organizing molecules into nanoscale structures and (ii) interfacing such nanostructures with macroscopically addressable components (e.g., metal and semiconductor electrodes). Molecular electronic device function thus rests fundamentally on charge transfer through organic and͞or biological molecules and across the interface between molecules and macroscopic electrodes (15, 16). Understanding of charge transfer mechanisms has mostly been based on average results of macroscopic measurements. The advent of scanning probe microscopies, along with other supersensitive techniques, has made it possible to characterize or directly observe charge transfer through organic molecules down to the nanoscale and single-molecule levels, as illustrated by measurements of singlemolecule conductivity (17-21) and probing of molecular switching and resonant tunneling (22,23). This, however, remains a daunting challenge for proteins, with difficulties arising from the assembly of suitable st...

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Mimicking Protein−Protein Electron Transfer: Voltammetry ofPseudomonas aeruginosaAzurin and theThermus thermophilusCu_ADomain at ω-Derivatized Self-Assembled-Monolayer Gold Electrodes

Cited by 122 publications

References 59 publications

Electrochemical study of an electron shuttle diheme protein: The cytochrome c from T. thermophilus

Electrochemical study of an electron shuttle diheme protein: The cytochrome c from T. thermophilus

Proton-Coupled Electron Transfer in Organic Synthesis: Fundamentals, Applications, and Opportunities

Long-range protein electron transfer observed at the single-molecule level: In situ mapping of redox-gated tunneling resonance

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