Protein-Matrix Solvation Dynamics in the α Subunit of <i>C</i>-Phycocyanin

Riter, Ruth R.; Edington, Maurice D.; Beck, Warren F.

doi:10.1021/jp960453j

Cited by 51 publications

(110 citation statements)

References 62 publications

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“…The 500 fs decay kinetic component further shows a strong correlation with the corresponding 500 fs 21 (PC trimers of Mastigocladus laminosus) and 690 fs 25 (PC α subunits of the AN112 mutant of the cyanobacterium Synechococcus PCC 6301) components, which were found in PC parts without the presence of all the compounds. Previous investigations 21,25 have been carried out on PC trimers and PC α-subunits while PC hexamers have also been investigated 9,24 and the presence of a linker was not reported. Furthermore, the kinetic component of 970 fs that was assigned to the energy transfer between the α and β cofactors in the PC trimer 9 is not consistent with the coupling that exists between the adjacent trimers in the PC hexamer.…”

Section: A Activation Of the Hoop In A Pc Rodmentioning

confidence: 84%

Activation and deactivation of vibronic channels in intact phycocyanin rods

Nganou¹,

David²,

Meinke³

et al. 2014

The Journal of Chemical Physics

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We investigated the excitation modes of the light-harvesting protein phycocyanin (PC) from Thermosynechococcus vulcanus in the crystalline state using UV and near-infrared Raman spectroscopy. The spectra revealed the absence of a hydrogen out-of-plane wagging (HOOP) mode in the PC trimer, which suggests that the HOOP mode is activated in the intact PC rod, while it is not active in the PC trimer. Furthermore, in the PC trimer an intense mode at 984 cm(-1) is assigned to the C-C stretching vibration while the mode at 454 cm(-1) is likely due to ethyl group torsion. In contrast, in the similar chromophore phytochromobilin the C5,10,15-D wag mode at 622 cm(-1) does not come from a downshift of the HOOP. Additionally, the absence of modes between 1200 and 1300 cm(-1) rules out functional monomerization. A correlation between phycocyanobilin (PCB) and phycoerythrobilin (PEB) suggests that the PCB cofactors of the PC trimer appear in a conformation similar to that of PEB. The conformation of the PC rod is consistent with that of the allophycocyanin (APC) trimer, and thus excitonic flow is facilitated between these two independent light-harvesting compounds. This excitonic flow from the PC rod to APC appears to be modulated by the vibration channels during HOOP wagging, C = C stretching, and the N-H rocking in-plan vibration.

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Section: A Activation Of the Hoop In A Pc Rodmentioning

confidence: 84%

Activation and deactivation of vibronic channels in intact phycocyanin rods

Nganou¹,

David²,

Meinke³

et al. 2014

The Journal of Chemical Physics

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“…This raises questions about the recent assignment of the observed ultra-fast solvation to protein dynamics. [63,64,84] …”

Section: Relevance Of Protein Vs Solventmentioning

confidence: 99%

“…are related to the total reorganisation energy by Table II gives values of the fitting parameters (E R , A j , τ j ) determined by fast laser spectroscopy for a range of chromophores and different environments, both protein and solvent. We do not claim the list is exhaustive of all the published values, but is meant to be indicative (For example, see also [25,63,64,86,87,88,89] ) We note the following general features.…”

Section: B Model 5 -Bound Watermentioning

confidence: 99%

Quantum Dynamics of Electronic Excitations in Biomolecular Chromophores: Role of the Protein Environment and Solvent

2008

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We consider continuum dielectric models as minimal models to understand the effect of a surrounding globular protein and solvent on the quantum dynamics of electronic excitations in a biological chromophore. For these models we derive expressions for the frequency dependent spectral density which describes the coupling of the electronic levels in the chromophore to its environment. The magnitude and frequency dependence of the spectral density determines whether or not the quantum dynamics is coherent or incoherent, and thus whether on not one can observe quantum interference effects such as Rabi oscillations. We find the contributions to the spectral density from each component of the chromophore environment: the bulk solvent, protein, and water bound to the protein. The relative importance of each component to the quantum dynamics of the chromophore is determined by the time scale on which one is considering the dynamics. Our results provide a natural explanation and model for the different time scales observed in the spectral density extracted from the solvation dynamics probed by ultra-fast laser spectroscopy techniques such as the dynamic Stokes shift and three pulse photon echo spectroscopy. Our results are used to define under what conditions the dynamics of the excited chromophore is dominated by the surrounding protein and when it is dominated by dielectric fluctuations in the solvent. We show that even when the chromophore is shielded from the solvent by the protein ultra-fast solvation can be dominated by the solvent. Hence, we suggest that the ultra-fast solvation recently seen in some biological chromophores should not necessarily be assigned to ultra-fast protein dynamics. The magnitudes of the spectral density that we estimate from our continuum models and extracted from experiment suggest that most quantum dynamics of electronic excitations is incoherent. A possible exception is transfer of excitons between neigbouring chromophores in photosynthetic systems.

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“…50 It may involve not only vibrational dynamics but also electronic dephasing and/or relaxation. Electronic dephasing and/or relaxation processes may occur on a time scale similar to that of the vibrational dynamics since the energy gaps of electronic states involved in 600-700 nm region (equivalent to 2381 cm -1 ) may be smaller than 2381 cm -1 .…”

Section: Dynamicsmentioning

confidence: 99%

Investigations of Ultrafast Exciton Dynamics in Allophycocyanin Trimer

et al. 2001

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The light-harvesting chromoprotein of cyanobacteria, allophycocyanin (APC), is studied both experimentally and theoretically. We observe fast kinetics and quantum beats in the pump-probe time-resolved profiles. Fourier analysis of the quantum beats provides eight vibrational frequencies: 186-215, 273-303, 352, 400, 449-469, 508, 625-664, and 840-879 cm -1 . We also measure anisotropy profiles which exhibit two types of kinetics; one has two fast (<1 ps) decay components, and the other almost shows no decay within 2 ps. To make use of the observed data in terms of a molecular description, the crude Born-Oppenheimer adiabatic approximation is applied to define both the electronic and vibrational states of the APC trimer. On the basis of this approximation, we construct a vibronic model, which describes the six chromophores in the APC trimer. With this molecular description, it is possible to study the steady-state optical properties and transient dynamics of the system. We analyze the absorption and CD spectra of the APC trimer, as well as oscillatory behaviors appearing in the pump-probe profiles and kinetics observed in the femtosecond anisotropy profile. We obtain a coherent set of properties of the potential energy surfaces of the system. On the basis of the vibronic model and using these molecular properties, we have simultaneously calculated the absorption and CD spectra in the spectral region 600-700 nm of the APC trimer. We have also simulated IC rate constant as a function of the electronic energy gap, electronic coupling constant, and promoting mode. Photorelated biosystems like the APC trimer may achieve an efficient IC by adjusting the electronic energy gap, promoting mode and vibronic coupling constant due to the breakdown of adiabatic approximation.

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Protein-Matrix Solvation Dynamics in the α Subunit of C-Phycocyanin

Cited by 51 publications

References 62 publications

Activation and deactivation of vibronic channels in intact phycocyanin rods

Activation and deactivation of vibronic channels in intact phycocyanin rods

Quantum Dynamics of Electronic Excitations in Biomolecular Chromophores: Role of the Protein Environment and Solvent

Investigations of Ultrafast Exciton Dynamics in Allophycocyanin Trimer

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