Excited‐State Dynamics of Fully Reduced Flavins and Flavoenzymes Studied at Subpicosecond Time Resolution

Enescu, Mironel; Lindqvist, Lars; Soep, B.

doi:10.1111/j.1751-1097.1998.tb02482.x

Cited by 33 publications

(62 citation statements)

References 21 publications

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“…For excited states with highly overlapping vibrational levels, (as in the flavin-localized excited states), the time scale of S n 3 S 1 relaxation is of the order of 1 psec or less. There is evidence from time-resolved absorption and fluorescence experiments on flavin compounds (31,32) that the internal conversion rate in the * singlet excited state manifold is a few hundred femtoseconds to 1 psec. Therefore, before ET, we expect that the donor excited state has relaxed to S 1 and is localized on the proximal side of the flavin ring, adjacent to the dimer.…”

Section: Resultsmentioning

confidence: 99%

Photoselected electron transfer pathways in DNA photolyase

Prytkova

Beratan

Skourtis

2007

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

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Cyclobutane dimer photolyases are proteins that bind to UVdamaged DNA containing cyclobutane pyrimidine dimer lesions. They repair these lesions by photo-induced electron transfer. The electron donor cofactor of a photolyase is a two-electron-reduced flavin adenine dinucleotide (FADH ؊ ). When FADH ؊ is photo-excited, it transfers an electron from an excited 3 * singlet state to the pyrimidine dimer lesion of DNA. We compute the lowest excited singlet states of FADH ؊ using ab initio (time-dependent density functional theory and time-dependent Hartree-Fock), and semiempirical (INDO͞S configuration interaction) methods. The calculations show that the two lowest 3 * singlet states of FADH ؊ are localized on the side of the flavin ring that is proximal to the dimer lesion of DNA. For the lowest-energy donor excited state of FADH ؊ , we compute the conformationally averaged electronic coupling to acceptor states of the thymine dimer. The coupling calculations are performed at the INDO͞S level, on donor-acceptor cofactor conformations obtained from molecular dynamics simulations of the solvated protein with a thymine dimer docked in its active site. These calculations demonstrate that the localization of the 1 FADH ؊ * donor state on the flavin ring enhances the electronic coupling between the flavin and the dimer by permitting shorter electron-transfer pathways to the dimer that have single through-space jumps. Therefore, in photolyase, the photo-excitation itself enhances the electron transfer rate by moving the electron towards the dimer.

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Section: Resultsmentioning

confidence: 99%

Photoselected electron transfer pathways in DNA photolyase

Prytkova

Beratan

Skourtis

2007

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

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“…There is evidence from time-resolved absorption and fluorescence experiments on flavin componds [18] that the internal conversion rate in the π* singlet excited state manifold is a few hundred fsec to a psec (especially for high energy Sn states). Therefore, since ET takes place in 200 psec, we expect that prior to ET the FADH − has relaxed to the S1 state that is localized on the proximal side of the flavin ring (figure 1).…”

Section: Resultsmentioning

confidence: 99%

Flavin Charge Transfer Transitions Assist DNA Photolyase Electron Transfer

Skourtis¹,

Prytkova²,

Beratan³

et al. 2007

AIP Conference Proceedings

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This contribution describes molecular dynamics, semi-empirical and ab-initio studies of the primary photo-induced electron transfer reaction in DNA photolyase. DNA photolyases are FADH − -containing proteins that repair UV-damaged DNA by photo-induced electron transfer. A DNA photolyase recognizes and binds to cyclobutatne pyrimidine dimer lesions of DNA. The protein repairs a bound lesion by transferring an electron to the lesion from FADH − , upon photoexcitation of FADH − with 350-450 nm light. We compute the lowest singlet excited states of FADH − in DNA photolyase using INDO/S configuration interaction, time-dependent densityfunctional, and time-dependent Hartree-Fock methods. The calculations identify the lowest singlet excited state of FADH − that is populated after photo-excitation and that acts as the electron donor. For this donor state we compute conformationally-averaged tunneling matrix elements to empty electron-acceptor states of a thymine dimer bound to photolyase. The conformational averaging involves different FADH − -thymine dimer confromations obtained from molecular dynamics simulations of the solvated protein with a thymine dimer docked in its active site. The tunneling matrix element computations use INDO/S-level Green's function, energy splitting, and Generalized Mulliken-Hush methods. These calculations indicate that photo-excitation of FADH − causes a π → π * charge-transfer transition that shifts electron density to the side of the flavin isoalloxazine ring that is adjacent to the docked thymine dimer. This shift in electron density enhances the FADH − -to -dimer electronic coupling, thus inducing rapid electron transfer.

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“…Ultrafast spectroscopic studies have recently been reported in several flavin enzymes (12)(13)(14)(15)(16). The fluorescence quenching of both RfBP and GOX was observed to occur on femtosecond and picosecond time scales by measurements of the excited-state flavin (RF* or FAD*) fluorescence decay (16).…”

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confidence: 99%

Femtosecond dynamics of flavoproteins: Charge separation and recombination in riboflavine (vitamin B ₂ )-binding protein and in glucose oxidase enzyme

Zhong

Zewail

2001

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

219

222

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Flavoproteins can function as hydrophobic sites for vitamin B2 (riboflavin) or, in other structures, with cofactors for catalytic reactions such as glucose oxidation. In this contribution, we report direct observation of charge separation and recombination in two flavoproteins: riboflavin-binding protein and glucose oxidase. With femtosecond resolution, we observed the ultrafast electron transfer from tryptophan(s) to riboflavin in the riboflavin-binding protein, with two reaction times: Ϸ100 fs (86% component) and 700 fs (14%). The charge recombination was observed to take place in 8 ps, as probed by the decay of the charge-separated state and the recovery of the ground state. The time scale for charge separation and recombination indicates the local structural tightness for the dynamics to occur that fast and with efficiency of more than 99%. In contrast, in glucose oxidase, electron transfer between flavin-adenine-dinucleotide and tryptophan(s)͞tyrosine(s) takes much longer times, 1.8 ps (75%) and 10 ps (25%); the corresponding charge recombination occurs on two time scales, 30 ps and nanoseconds, and the efficiency is still more than 97%. The contrast in time scales for the two structurally different proteins (of the same family) correlates with the distinction in function: hydrophobic recognition of the vitamin in the former requires a tightly bound structure (ultrafast dynamics), and oxidation-reduction reactions in the latter prefer the formation of a chargeseparated state that lives long enough for chemistry to occur efficiently. Finally, we also studied the influence on the dynamics of protein conformations at different ionic strengths and denaturant concentrations and observed the sharp collapse of the hydrophobic cleft and, in contrast, the gradual change of glucose oxidase. D ynamical processes in proteins play a crucial role in biological structure-function correlations (1, 2), and one such process is electron transfer (ET). In biological systems, ET reactions are ubiquitous (3, 4), especially in enzymes with redox reactions (5). Flavoproteins with flavin chromophores are examples of such enzymes and are involved in various catalytic processes (6-8). The understanding of ET reactions of flavins in proteins and their redox reactions is critical to the enzyme function.In this contribution, we report our femtosecond studies of ET dynamics of riboflavin (RF; vitamin B 2 ) in RF-binding protein (RfBP) and flavin-adenine-dinucleotide (FAD) in glucose oxidase (GOX) ( Fig. 1 and Scheme 1). High-resolution x-ray crystallographic structures of both proteins have recently been reported, and the binding structures of flavins in the proteins are well determined (9-11). RfBP is a globular monomeric protein of approximate dimensions 50 ϫ 40 ϫ 35 Å with a single polypeptide chain of 219 amino acids, nine disulfide bridges, six ␣-helices, and four series of discontinuous areas of ␤ structure.The ligand-binding domain of RfBP is a hydrophobic cleft, Ϸ20 Å wide and 15 Å deep. The binding of RF occurs in the cleft with...

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Excited‐State Dynamics of Fully Reduced Flavins and Flavoenzymes Studied at Subpicosecond Time Resolution

Cited by 33 publications

References 21 publications

Photoselected electron transfer pathways in DNA photolyase

Photoselected electron transfer pathways in DNA photolyase

Flavin Charge Transfer Transitions Assist DNA Photolyase Electron Transfer

Femtosecond dynamics of flavoproteins: Charge separation and recombination in riboflavine (vitamin B ₂ )-binding protein and in glucose oxidase enzyme

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Excited‐State Dynamics of Fully Reduced Flavins and Flavoenzymes Studied at Subpicosecond Time Resolution

Cited by 33 publications

References 21 publications

Photoselected electron transfer pathways in DNA photolyase

Photoselected electron transfer pathways in DNA photolyase

Flavin Charge Transfer Transitions Assist DNA Photolyase Electron Transfer

Femtosecond dynamics of flavoproteins: Charge separation and recombination in riboflavine (vitamin B 2 )-binding protein and in glucose oxidase enzyme

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Femtosecond dynamics of flavoproteins: Charge separation and recombination in riboflavine (vitamin B ₂ )-binding protein and in glucose oxidase enzyme