The Search for Relay Stations. Long-distance Electron Transfer in Peptides

Giese, Bernd; Kracht, Sonja; Cordes, Meike

doi:10.2533/chimia.2013.855

Cited by 8 publications

(6 citation statements)

References 13 publications

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“…Based on this concept, Giese et al developed an assay of the radical cation of dialkoxyl phenylalanine as the electron acceptor, tyrosine as the electron donor and prolines as spacers for ET from the donor to the acceptor. 36 The electron acceptor of a precursor was produced via laser flash photolysis that yielded the desired aromatic cation radical as shown in Scheme 2 (2 -5). 36 The radical cation having a less positive oxidation potential than proline was selected to avoid the oxidation of proline.…”

Section: Effect Of Peptide Chain Length -Hopping Versus Tunnelingmentioning

confidence: 99%

Electron transfer in peptides

et al. 2015

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In this review, we discuss the factors that influence electron transfer in peptides. We summarize experimental results from solution and surface studies and highlight the ongoing debate on the mechanistic aspects of this fundamental reaction. Here, we provide a balanced approach that remains unbiased and does not favor one mechanistic view over another. Support for a putative hopping mechanism in which an electron transfers in a stepwise manner is contrasted with experimental results that support electron tunneling or even some form of ballistic transfer or a pathway transfer for an electron between donor and acceptor sites. In some cases, experimental evidence suggests that a change in the electron transfer mechanism occurs as a result of donor-acceptor separation. However, this common understanding of the switch between tunneling and hopping as a function of chain length is not sufficient for explaining electron transfer in peptides. Apart from chain length, several other factors such as the extent of the secondary structure, backbone conformation, dipole orientation, the presence of special amino acids, hydrogen bonding, and the dynamic properties of a peptide also influence the rate and mode of electron transfer in peptides. Electron transfer plays a key role in physical, chemical and biological systems, so its control is a fundamental task in bioelectrochemical systems, the design of peptide based sensors and molecular junctions. Therefore, this topic is at the heart of a number of biological and technological processes and thus remains of vital interest.

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Section: Effect Of Peptide Chain Length -Hopping Versus Tunnelingmentioning

confidence: 99%

Electron transfer in peptides

et al. 2015

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“…Although the ET rate through this fragment under indicated experimental conditions could be high, the presence of two additional low conductive fragments (fragments 1 and 3) forming insulating barriers on both sides of the central fragment would make ET through an entire PilA unlikely even assuming that the protein is not denaturated under these high bias voltages. One possible scenario is that overlapping regions of fragment 2 in filaments comprised of PilA proteins (formation of pilus filaments and bundles) might enable tunneling along the filaments . However, our analysis of the effect of amino acid pairing (conformer #4 vs. conformer #1) and the results of the recent analysis of entire protein conductance based on a non coherent model indicate that electron coherent tunneling through aromatic amino acid residues cannot describe conductivity of the pili composed of PilA bundles either.…”

Section: Introductionmentioning

confidence: 63%

“…One possible scenario is that overlapping regions of fragment 2 in filaments comprised of PilA proteins (formation of pilus filaments and bundles) might enable tunneling along the filaments. 12,18,21 However, our analysis of the effect of amino acid pairing (conformer #4 vs. conformer #1) and the results of the recent analysis of entire protein conductance based on a non coherent model 13 indicate that electron coherent tunneling through aromatic amino acid residues cannot describe conductivity of the pili composed of PilA bundles either.…”

Section: Full Papermentioning

confidence: 76%

“…Except for an initial estimation of the electrostatic potential profile and molecular orbital (MO) energy and spatial localization in a model constructed by similarity to other filamentous proteins, little is known about the mechanism of conductivity of PilA (see also, related discussion on extracellular ET in Shewanella ). In the framework of the “metal–like” model, it was proposed that pili aromatic amino acids are responsible for the pili conductivity and they have mutual orientation similar to heavily doped organic polymers allowing for efficient MO delocalization due to π–π interaction enabling longitudinal ET . In supporting this mechanism, Feliciano et al, constructed a hypothetical pilin subunit based on homology modeling using another filamentous pili IV protein, Pseudomonas aeruginosa PAK pilin, as a template and calculated MO energies, delocalization and longitudinal potential profile along the constructed peptide .…”

Section: Introductionmentioning

confidence: 99%

“…In the framework of the "metal-like" model, it was proposed that pili aromatic amino acids are responsible for the pili conductivity and they have mutual orientation similar to heavily doped organic polymers allowing for efficient MO delocalization due to p-p interaction enabling longitudinal ET. 6,10,[17][18][19][20][21] In supporting this mechanism, Feliciano et al, constructed a hypothetical pilin subunit based on homology modeling using another filamentous pili IV protein, Pseudomonas aeruginosa PAK pilin, as a template and calculated MO energies, delocalization and longitudinal potential profile along the constructed peptide. 10 The results clearly demonstrate the absence of MO delocalization along the entire peptide, and though the calculation of the ET rate was not performed, the authors concluded that the conductivity along the peptide is possible by hopping between aromatic amino acids.…”

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confidence: 99%

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On the electron transfer through Geobacter sulfurreducens PilA protein

Lebedev

Mahmud

Griva

et al. 2015

J. Polym. Sci. Part B: Polym. Phys.

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Geobacter sulfurreducens pili composed of the Type IV pili structural peptide PilA have been implicated as efficient electronic conductors. Though investigated experimentally, no detailed theoretical studies have been performed to date that provide quantitative estimation of the transmission spectrum, electron transfer (ET) paths, efficiency of current generation, and other factors needed for understanding possible mechanisms of conductivity. In the present work, we calculate from first principles the possibilities of electron tunneling through 3 PilA fragments which structure was identified recently by NMR. The results indicate that positively charged amino acids, arginines and lysines form electrostatic traps in the middle of the peptide preventing ET at low bias voltages (<∼6 V). At higher biases the traps are filled with electrons making possible sequential electron tunneling through the central part of the protein. In addition, leucines and phenylalanines form ET loops facilitating electron stabilization within the protein and sequential ET. Our results indicate that ET through the PilA protein cannot occur by coherent ET, but suggest a sequential (incoherent) mechanism. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2015, 53, 1706–1717

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Proline as a charge stabilizing amino acid in peptide radical cations

Monney

Bally

Giese

2015

J of Physical Organic Chem

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Long distance electron transfer in proteins requires relay stations that can be transitorily oxidized or reduced. Although individual prolines cannot assume this function, because of their high ionization energy, it has been shown that polyprolines have the ability to transfer charges. In order to determine the role of the proline in the hole distribution and transport within a PheProPhe tripeptide, the radical cation of a model compound where the phenylalanines carry two or three methoxy groups, respectively, was generated by flash photolysis. Surprisingly, after equilibration, about two thirds of the holes were found to reside on the phen(OMe) 2 instead of the more easily oxidizable phen(OMe) 3 moiety. DFT calculations showed that, in most of the accessible conformations, the phen(OMe) 2• + -moiety profits more from stabilization by N-and/or O-lone pairs of neighboring amide groups than the phen(OMe) 3• + moiety can, which explains the apparently counterthermodynamic hole distribution. Similar calculations showed that, in several conformers of the natural PheProPhe radical cation, the unpaired electron is delocalized over two amide groups, by residing in a σ MO which links the N-lone pair of the central proline unit with the O-lone pair of a proximate amino acid, through hyperconjugation via the intervening C-C α σ-bond. The same pattern is found in a model compound, N-acetylproline dimethylamide. It seems that prolines favor conformers which foster hyperconjugation of two amide groups, which lowers the ionization energy of peptides. One should thus consider such interacting amide groups as potential relay stations in the course of electron transfer in polyprolines.

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The Search for Relay Stations. Long-distance Electron Transfer in Peptides

Abstract: Nature uses peptide aggregates as soft materials for electron transfer over long distances. These reactions occur in a multistep hopping reaction with various functional groups as relay stations that are located in the side chain and in the backbone of the peptides.

Cited by 8 publications

References 13 publications

Electron transfer in peptides

Electron transfer in peptides

On the electron transfer through Geobacter sulfurreducens PilA protein

Proline as a charge stabilizing amino acid in peptide radical cations

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