Long-range electron transfer in peptides. Tyrosine reduction of the indolyl radical: reaction mechanism, modulation of reaction rate, and physiological considerations

Mishra, Awadhesh Kumar; Chandrasekar, Ramamurthy; Faraggi, M.; Klapper, Michael H.

doi:10.1021/ja00083a029

Cited by 75 publications

(83 citation statements)

References 6 publications

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“…Although through-bond PET has been observed in polyprolines separating strong organic donors and acceptors (33)(34)(35)(36), any significant contribution in these experiments can be ruled out by the observation of Ϸ100% QY for the R6G-Trp conjugate (in which intramolecular complex formation is prevented by the short and stiff linker), the use of saturated alkyl chains as fluorophore linker, and the steep sigmoidal distance dependence observed for MR113-Trp conjugates.…”

Section: Steady-state Fluorescence Quenching Experiments Of Polyprolinementioning

confidence: 89%

Probing polyproline structure and dynamics by photoinduced electron transfer provides evidence for deviations from a regular polyproline type II helix

Doose

Neuweiler

Barsch

et al. 2007

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

117

142

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Polyprolines are well known for adopting a regular polyproline type II helix in aqueous solution, rendering them a popular standard as molecular ruler in structural molecular biology. However, single-molecule spectroscopy studies based on Fö rster resonance energy transfer (FRET) have revealed deviations of experimentally observed end-to-end distances of polyprolines from theoretical predictions, and it was proposed that the discrepancy resulted from dynamic flexibility of the polyproline helix. Here, we probe end-to-end distances and conformational dynamics of poly-Lprolines with 1-10 residues using fluorescence quenching by photoinduced-electron transfer (PET). A single fluorophore and a tryptophan residue, introduced at the termini of polyproline peptides, serve as sensitive probes for distance changes on the subnanometer length scale. Using a combination of ensemble fluorescence and fluorescence correlation spectroscopy, we demonstrate that polyproline samples exhibit static structural heterogeneity with subpopulations of distinct end-to-end distances that do not interconvert on time scales from nano-to milliseconds. By observing prolyl isomerization through changes in PET quenching interactions, we provide experimental evidence that the observed heterogeneity can be explained by interspersed cis isomers. Computer simulations elucidate the influence of trans/ cis isomerization on polyproline structures in terms of end-to-end distance and provide a structural justification for the experimentally observed effects. Our results demonstrate that structural heterogeneity inherent in polyprolines, which to date are commonly applied as a molecular ruler, disqualifies them as appropriate tool for an accurate determination of absolute distances at a molecular scale.fluorescence correlation spectroscopy ͉ molecular ruler ͉ prolyl isomerization ͉ biopolymer ͉ Förster resonance energy transfer F luorescence spectroscopy provides a variety of tools to measure distances, monitor dynamics, or observe molecular interactions with sensitivity far beyond that of other biophysical techniques. Distance-dependent interactions between fluorophores and fluorescence-quenching molecular compounds, such as Förster resonance energy transfer (FRET) or photoinduced electron transfer (PET), are capable of reporting on processes on the nanometer length scale, below the diffraction limit generally imposed on optical techniques. Although much information is gained from relative distances or distance changes, the quest for precise determination of absolute distances has been ongoing ever since Stryer and Haugland presented the application of FRET as a spectroscopic ruler (1). FRET is a nonradiative dipole-dipole interaction between two fluorophores (donor D and acceptor A) that can serve as a spectroscopic ruler on length scales between Ϸ2 and Ϸ10 nm (2-6). Structurally well defined model systems (molecular rulers) are needed for validation of spectroscopic rulers as much as the latter are essential for structural investigations. Since the sem...

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Section: Steady-state Fluorescence Quenching Experiments Of Polyprolinementioning

confidence: 89%

Probing polyproline structure and dynamics by photoinduced electron transfer provides evidence for deviations from a regular polyproline type II helix

Doose

Neuweiler

Barsch

et al. 2007

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

117

142

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“…This pathway is characterized by a low value of the descriptor of the exponential distance dependence of the electron transfer rate, β ΤΒ = 2.5 ± 0.1 nm -1 , suggesting that helical segments in proteins can function as efficient channels of long-distance electron transfer. Long-range electron transfer (LRET) between various oligoproline-bridged redox pairs has been studied over the past 10 years in several laboratories (1)(2)(3)(4)(5)(6)(7)(8)(9)(10)(11)(12)(13)(14)(15)(16)(17)(18) with the aim of elucidating the parameters of LRET across a single peptide pathway. The choice of oligoprolines for such a study was dictated by the known ability of short H-(Pro)n-OH peptides to attain, in aqueous solution, a stable helical conformation similar to that of the 3X left-handed helix of alltrans poly-L-proline II (19)(20)(21)(22).…”

Section: Risø National Laboratory Dk-4000 Roskilde Denmarkmentioning

confidence: 99%

Long-Range Electron Transfer Between Proline-Bridged Aromatic Amino Acids

Bobrowski

Poznański

Holcman

et al. 1998

Advances in Chemistry

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Interpretation of the kinetic pulse radiolysis data for intramolecular Trp --> Tyr radical transformation in aqueous solutions of linear H-Trp-(Pro)n-Tyr-OH, n = 0-5, is presented in terms of the Marcus electron transfer theory, taking into account conformational dynamics of the molecules. For this purpose, for each peptide, representative sets of low-energy conformers were selected with the help of experimental methods ( 1 H and 13 C NMR, and circular dichroism) and modeling meth ods (molecular mechanics and dynamics ); and relative electron transfer rates averaged over all the conformers were calculated for two assumed competitive electron transfer pathways: through space (TS) and through the peptide backbone (TB). The TS rates were obtained by taking into account the overlap integrals of aromatic ring orbitals calu lated quantum mechanically. By fitting the calculated rates to the experi mental data for the rate constants for electron transfer, ket, with an exponential function appropriate for the two-pathway model, we have demonstrated that in linear short-bridged peptides (n = 0-2), electron transfer predominantly takes the TS pathway, which consists of van der Waals contacts between the aromatic rings, whereas in longer peptides (n = 3-5), it occurs exclusively by the TB pathway, which is made of a -(Pro)n-bridge in a helical conformation similar to that of all-trans poly-L-proline II. This pathway is characterized by a low value of the descriptor of the exponential distance dependence of the electron transfer rate, β ΤΒ = 2.5 ± 0.1 nm -1 , suggesting that helical segments in proteins can function as efficient channels of long-distance electron transfer.

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“…The latter is usually realized by through-space, through-bond, and through nonvalent interaction modes, depending on the distances and the properties of the bridges between two residues [92,[94][95][96]. It should be noted that, in addition to low IPs, the phenol group of Tyr or the indole group of Trp also are more acidic, which is inclined to lose their protons, when the residues release or convey an electron to others in proteins.…”

Section: Proton-regulated Hole Hopping Migrationmentioning

confidence: 99%

Peptides-assisted charge transfers in proteins: relay mechanism and its controllability

2010

Front. Chem. China

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This feature article addresses several novel aspects regarding the peptide-mediated charge migrations, including: i) radical exchanges with tunable radical types (σ-radical versus π-radical) and electron-transfer (ET)-channel-tunable cooperative protoncoupled ET (PCET) mechanism, including hydrogen-atom transfer (HAT), single ETchannel PCET, double ET channel PCET, and channel-type-tunable (σ-channel versus π-channel) PCET; ii) hole hopping migration between the active groups in the side-chains and its controllability; iii) hole hopping through stepping-stones via a solvated "hole" form; and iv) electron hopping through positively charged groups as stepping-stones via a solvated electron state. In particular, the controllability of the ET channels (pathways and types) and solvated-"hole"/"electron"-based relay mechanisms are mainly mentioned. Clearly, this is an important addition to the well-documented mechanisms for charge migration in proteins. In view of the complexity of protein charge migration, further exploration on details of the steppingstone-based relay mechanisms, by considering the properties and structures of the redox active centers, their intercalators, and the real surroundings, is still needed.

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Long-range electron transfer in peptides. Tyrosine reduction of the indolyl radical: reaction mechanism, modulation of reaction rate, and physiological considerations

Cited by 75 publications

References 6 publications

Probing polyproline structure and dynamics by photoinduced electron transfer provides evidence for deviations from a regular polyproline type II helix

Probing polyproline structure and dynamics by photoinduced electron transfer provides evidence for deviations from a regular polyproline type II helix

Long-Range Electron Transfer Between Proline-Bridged Aromatic Amino Acids

Peptides-assisted charge transfers in proteins: relay mechanism and its controllability

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