Amino Acid Protonation States Determine Binding Sites of the Secondary Ubiquinone and Its Anion in the <i>Rhodobacter sphaeroides</i> Photosynthetic Reaction Center

Grafton, Anthony K.; Wheeler, Ralph A.

doi:10.1021/jp9901139

Cited by 62 publications

(70 citation statements)

References 92 publications

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“…This shift may be correlated to the observed position of Q B in the structure of this RC variant in its neutral state, which is in the proximal position to the non-heme iron (45). This position has been suggested to require GluL212 and AspL213 to be protonated (28). This result would in turn reduce the strength of the interactions within the cluster in the L209PY mutant, consistently with the observed acidic shift of the H ϩ ͞Q B Ϫ curve.…”

Section: Protonation Events Triggered By the Q Bsupporting

confidence: 64%

“…The partial protonation events that occur on Q A Ϫ and Q B Ϫ formations have been studied by spectroscopic techniques by using site-directed mutagenesis (9)(10)(11)(12)(13)(14)(15)(16)(17)(18)(19)(20)(21)(22) and by numerical methods (23)(24)(25)(26)(27)(28)(29)(30). There is a general agreement that the major response of the protein to the Q B Ϫ formation is the change of the ionization state of acidic residues situated in the Q B environment.…”

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confidence: 99%

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Key role of proline L209 in connecting the distant quinone pockets in the reaction center of Rhodobacter sphaeroides

Tandori

Maróti

Alexov

et al. 2002

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

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T he biological role of bacterial reaction center (RC) membrane proteins is to convert light energy into chemical free energy. The sequential absorption of two photons by the system results into the production of the doubly reduced and doubly protonated form of the ultimate electron acceptor of the complex, a ubiquinone (Q B ). The formed Q B H 2 molecule then delivers its reducing power to the cytochrome bc1 complex, resulting in the release of protons on the periplasmic side of the membrane. The resulting transmembrane proton gradient drives ATP synthesis through the ATP synthase. The reduction of Q B coupled to the uptake of protons from the bulk is an important step shared by many systems involved either in photosynthesis or in respiratory chains (1).The three-dimensional structure of the reaction center from the purple photosynthetic bacterium Rhodobacter (Rb.) sphaeroides is known at atomic resolution (2-4). Three subunits with a total molecular weight of about 100 kDa compose these RCs. The transmembrane L and M subunits carry the nine pigments and cofactors: four bacteriochlorophylls, two bacteriopheophytins, two ubiquinones 10, and one non-heme iron atom. The third subunit, H, caps the reaction center on the cytoplasmic side of the membrane. The initial photochemical event induced by the absorption of a photon is the creation of the singlet excited state of a dimer of bacteriochlorophylls (P3P*), which constitutes the primary electron donor. P* is a strong reducing species that initiates the electron transfer reaction through the protein. In about 200 ps, the charge separation occurs between P and the first quinone electron acceptor, Q A , situated on the cytoplasmic side of the complex. The electron is then transferred from Q A Ϫ to a secondary quinone Q B within 10-100 s (5-7). Both Q A and Q B are deeply buried within the reaction center protein. The role of the protein in stabilizing the redox species is essential to ensure high forward electron transfer rates and to prevent charge recombinations to occur. Although chemically identical, Q A and Q B behave differently. Q A , bound to the M subunit in a relatively hydrophobic pocket, functions as one electron acceptor and is never protonated. At variance, Q B , bound to the L subunit, is surrounded by charged and polar residues and behaves as a two-electron gate, accepting sequentially two electrons from Q A and two protons from the cytoplasm. In chromatophores, the semiquinone Q B Ϫ can bind a proton below pH 6.8 (8). However, in isolated RCs, the semiquinones are not directly protonated but induce the shift of the pKas of ionizable interacting residues, which results in substoichiometric proton uptake by the protein (9, 10). The proton uptake may occur through a number of water molecules and protonatable amino acid residues situated between Q B and the cytoplasmic surface. Of main interest is to identify the dynamical and structural role of the protein that contributes to the stability of the Q A Ϫ and Q B Ϫ states and to the energetic and functiona...

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Section: Protonation Events Triggered By the Q Bsupporting

confidence: 64%

mentioning

confidence: 99%

Key role of proline L209 in connecting the distant quinone pockets in the reaction center of Rhodobacter sphaeroides

Tandori

Maróti

Alexov

et al. 2002

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

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“…We propose a model for the first electron transfer to Q B that accounts for the observation of a single binding site for ubiquinone in Fourier transform IR difference studies (41,42), the dependence of ubiquinone position on the protonation or position of ionizable residues within the Q B pocket, as suggested by simulations (22,23,(44)(45)(46), and the observed distal binding of ubiquinone in the dark (16)(17)(18)21). The distal binding site is a metastable binding site for neutral ubiquinone, but it does not correspond to a conformational gate in the reaction.…”

Section: Discussionmentioning

confidence: 99%

“…In R. sphaeroides, the ubiquinone was found to occupy the distal or proximal binding sites in both neutral and semianionic states. The site occupied depended on the protonation state assigned to Glu-L212 and Asp-L213 (22). In B. viridis, spontaneous movement from the distal site to the proximal site depended on the initial orientation of the quinone in the distal site in both the PQ A Q B and P ϩ Q B Ϫ states (23).…”

mentioning

confidence: 99%

Time-resolved crystallographic studies of light-induced structural changes in the photosynthetic reaction center

Baxter

Ponomarenko

Šrajer

et al. 2004

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

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Light-induced structural changes in the bacterial reaction center were studied by a time-resolved crystallographic experiment. Crystals of protein from Blastochloris viridis (formerly Rhodopseudomonas viridis) were reconstituted with ubiquinone and analyzed by monochromatic and Laue diffraction, in the dark and 3 ms after illuminating the crystal with a pulsed laser (630 nm, 3 mJ͞pulse, 7 ns duration). Refinement of monochromatic data shows that ubiquinone binds only in the ''proximal'' Q B binding site. No significant structural difference was observed between the light and dark datasets; in particular, no quinone motion was detected. This result may be reconciled with previous studies by postulating equilibration of the ''distal'' and ''proximal'' binding sites upon extended dark adaption, and in which movement of ubiquinone is not the conformational gate for the first electron transfer between Q A and QB.bacterial photosynthesis ͉ secondary electron transfer ͉ Laue diffraction ͉ time-resolved crystallography ͉ quinones

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“…The conformation movements allow us to use photo thermal phenomena, like photacoustic (Edens et al, 1999;Nagy et al, 2001), or transient grating Ohmori et al, 2008) measurements. Computer science develops faster and faster providing more and more memory and speed and in this way the presentation of these big proteins is also more widespread and precise (Grafton and Wheeler, 1999;Rabenstein, 1998).…”

Section: Rc Is An Excellent Model Proteinmentioning

confidence: 99%

Photosynthetic Reaction Centres-from Basic Research to Application

Nagy¹,

HAJDU²,

FISHER³

et al. 2010

Not Sci Biol

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There is no doubt that studying the photosynthetic conversion of light into chemical energy is extremely important in many points of view: 1) technical-in order to improve the utilization of the solar energy; 2) food production -to improve the photosynthetic production of plants in agriculture; 3) ecology -keeping the primer production in ecosystems in the biosphere balanced, etc. In the photosynthetic reaction centre protein, RC, light energy is converted by a quantum yield of almost unity. There is no such a system designed by human which is able to do that. The RC purified from purple bacteria provides an extremely unique system for studying the requirements for high efficiency conversion of light into electrochemical energy. Thanks to the recent structural (e.g. crystallography (Nobel prize to Michel, Deisenhofer, Huber) and functional (Nobel prize to Marcus)) results together with the works of molecular biology, computerand electro-techniques, a wealth of information made a relatively clear picture about the kinetics, energetics and stabilization of electron transport within this protein that opens possibilities for new generation practical applications. In this paper we provide a short summary of fields in which the reaction centre protein can be important from practical points of view.

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Amino Acid Protonation States Determine Binding Sites of the Secondary Ubiquinone and Its Anion in the Rhodobacter sphaeroides Photosynthetic Reaction Center

Cited by 62 publications

References 92 publications

Key role of proline L209 in connecting the distant quinone pockets in the reaction center of Rhodobacter sphaeroides

Key role of proline L209 in connecting the distant quinone pockets in the reaction center of Rhodobacter sphaeroides

Time-resolved crystallographic studies of light-induced structural changes in the photosynthetic reaction center

Photosynthetic Reaction Centres-from Basic Research to Application

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