Proline as a charge stabilizing amino acid in peptide radical cations

Monney, Nicolas P.-A.; Bally, Thomas; Giese, Bernd

doi:10.1002/poc.3416

Cited by 8 publications

(12 citation statements)

References 37 publications

(18 reference statements)

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“…Reanalysis of the laser experiments now revealed small amounts of an intermediate at 385 nm (Figure S3), and this agrees with the literature value for a dialkyl thioether radical cation that is stabilised by a neighbouring pyrrolidine amide . This finding indicates that neighbouring proline moieties in 1 c enable Met to function as a relay amino acid in ET processes by lowering its redox potential …”

Section: Figurementioning

confidence: 99%

Amide Neighbouring‐Group Effects in Peptides: Phenylalanine as Relay Amino Acid in Long‐Distance Electron Transfer

et al. 2018

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In nature, proteins serve as media for long-distance electron transfer (ET) to carry out redox reactions in distant compartments. This ET occurs either by a single-step superexchange or through a multi-step charge hopping process, which uses side chains of amino acids as stepping stones. In this study we demonstrate that Phe can act as a relay amino acid for long-distance electron hole transfer through peptides. The considerably increased susceptibility of the aromatic ring to oxidation is caused by the lone pairs of neighbouring amide carbonyl groups, which stabilise the Phe radical cation. This neighbouring-amide-group effect helps improve understanding of the mechanism of extracellular electron transfer through conductive protein filaments (pili) of anaerobic bacteria during mineral respiration.

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Section: Figurementioning

confidence: 99%

Amide Neighbouring‐Group Effects in Peptides: Phenylalanine as Relay Amino Acid in Long‐Distance Electron Transfer

et al. 2018

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“…26 ■ RESULTS AND DISCUSSION Ac-Gly-NHMe (1). In a previous paper, 22 we demonstrated that the radical cation of the tripeptide PheProPhe can be localized exclusively on its backbone. To gain more detailed insight into this phenomenon, we used the simple model compound, Ac-Gly-NHMe (1).…”

Section: ■ Methods Of Calculationmentioning

confidence: 99%

“…27,28 In conformer 1A •+ , the spin is delocalized over an (OC)NC α CO unit, in the same fashion as in several conformers of PheProPhe tripeptide we discussed previously. 22 The shape of the singly occupied MO (SOMO) shows that the C α C bond serves as a hyperconjugative mediator for the through bond delocalization of the spin between the nonbonding π-HOMO of the C-terminal amide moiety and the in-plane p-AO of the carbonyl oxygen atom of the N-terminal amide (cf. Figure 1).…”

Section: ■ Methods Of Calculationmentioning

confidence: 99%

“…21 However, we have recently shown that the backbone of proline within a peptide can stabilize a radical cation by the hyperconjugative effect. 22 Therefore, we raised the question whether prolines could act as relay stations for electron hole tranfer through a PPII helix. In this paper, we investigate all possible interactions that stabilize a radical cation on the backbone of a peptide, and especially on a polyproline.…”

Section: ■ Introductionmentioning

confidence: 99%

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Electronic Structure of Hole-Conducting States in Polyprolines

2015

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Electron transfer over long distances in proteins by a hopping process requires transient relay stations that can harbor charge and spin for a short time span. Certain easily oxidizable or reducible side chains may assume that role, but it has been shown that charge transport in peptides can also take place in the absence of such groups which implies that the peptide backbone provides for hopping stations. We have identified three different types of radical cation states in such peptides that are associated with significantly lower ionization potentials than those of the constituent amino acids, and which may thus serve as relay stations for hole transport. Which of these states is the most stable one depends on the nature and the conformation of the peptide. In contrast to α-helices which, due to their high dipole moments, can only form stable radical cation states that are localized on the C-terminal amino acids, polyprolines are capable of accommodating such states inside the PPII helices and those states may serve as relay stations for hole transfer through polyprolines. Of which type these states are depends often on small conformational changes, and sometimes the most stable states are hybrids of the three types we have identified. ■ INTRODUCTIONThe transport of positive or negative charges over long distances is an essential function in living organisms. 1−3 For distances greater than ca. 2 nm, electron transfer in proteins can only occur in a multistep hopping process via "stepping stones" that are transiently oxidized or reduced during the process. 4,5 These relay stations allow one long and therefore very slow single step electron transfer to be divided into several short but quick steps which make that the rate of the electron transfer via multistep hopping decreases only slightly with the total distance between the electron donor and acceptor. 6,7 Several protein side groups were shown to be able to act as stepping stones in the course of hole transfer in proteins. They can be divided into two groups, the aromatic moieties in tyrosine, tryptophan, and imidazole, and the sulfur containing side chains in cysteine or methionine. The efficiency of the first group to serve as stepping stones is due to their low oxidation or reduction potentials, respectively. 8−10 Methionine on the other hand can only serve as a hole stepping stone if the oxidized sulfur lone pair is stabilized by a nearby aromatic or amide moiety. 11−14 It was also shown that, even in the absence of the above-mentioned side groups, the backbones of α-and 3 10 -helices or β-turns can serve as relay stations. In the case of these structures, a large dipole moment decreases the oxidation potential especially at the C-termini of such structures. 6,15−17 Another secondary structure is the so-called PPII helix which is found in most peptides including electron transport proteins like cytochrome C551 of Pseudomonas aeruginosa or bacteriochlorophyll A in the photosynthetic bacterium Prosthecochloris aestuarii. 18 A major component of...

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“…This secondary structure is important for ET studies in peptides [13] because theoretical studies support the charge-conducting properties [14] and identify prolines as charge stabilizing amino acid. [15] We placed the flavin as electron acceptor (= electron hole donor) at the N-terminus to promote the ET by the intrinsic peptide dipole. [16] Trps were placed with 1-3 intervening prolines in P1-P3 and serve as electron donors (= electron hole acceptors) to direct the electron transfer.…”

Section: Introductionmentioning

confidence: 99%

Directed Electron Transfer in Flavin Peptides with Oligoproline‐Type Helical Conformation as Models for Flavin‐Functional Proteins

et al. 2020

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To mimic the charge separation in functional proteins we studied flavin‐modified peptides as models. They were synthesized as oligoprolines that typically form a polyproline type‐II helix, because this secondary structure supports the electron transfer properties. We placed the flavin as photoexcitable chromophore and electron acceptor at the N‐terminus. Tryptophans were placed as electron donors to direct the electron transfer over 0–3 intervening prolines. Spectroscopic studies revealed competitive photophysical pathways. The reference peptide without tryptophan shows dominant non‐specific ET dynamics, leading to an ion pair formation, whereas peptides with tryptophans have weak non‐specific ET and intensified directed electron transfer. By different excitation wavelengths, we can conclude that the corresponding ion pair state of flavin within the peptide environment has to be energetically located between the S1 and S4 states, whereas the directed electron transfer to tryptophan occurs directly from the S1 state. These photochemical results have fundamental significance for proteins with flavin as redoxactive cofactor.

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Proline as a charge stabilizing amino acid in peptide radical cations

Cited by 8 publications

References 37 publications

Amide Neighbouring‐Group Effects in Peptides: Phenylalanine as Relay Amino Acid in Long‐Distance Electron Transfer

Amide Neighbouring‐Group Effects in Peptides: Phenylalanine as Relay Amino Acid in Long‐Distance Electron Transfer

Electronic Structure of Hole-Conducting States in Polyprolines

Directed Electron Transfer in Flavin Peptides with Oligoproline‐Type Helical Conformation as Models for Flavin‐Functional Proteins

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