Ubiquinone Binding, Ubiquinone Exclusion, and Detailed Cofactor Conformation in a Mutant Bacterial Reaction Center

McAuley, Katherine; Fyfe, Paul K.; Ridge, Justin P.; Cogdell, Richard J.; Isaacs, Neil W.; Jones, Michael R.

doi:10.1021/bi000557r

Cited by 77 publications

(125 citation statements)

References 59 publications

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“…It is bound in the proximal position in RCs carrying the A(M260)W mutation close to Q A [20], the E(L212)A-D(L213)A mutations near Q B [15], and the P(L209)Y mutation that is 9…”

Section: Introductionmentioning

confidence: 99%

Temperature and cryoprotectant influence secondary quinone binding position in bacterial reaction centers

et al. 2004

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We have determined the first de novo position of the secondary quinone Q B in the Rhodobacter sphaeroides reaction center (RC) using phases derived by the single wavelength anomalous dispersion method from crystals with selenomethionine substitution. We found that in frozen RC crystals, Q B occupies primarily the proximal binding site. In contrast, our room temperature structure showed that Q B is largely in the distal position. Both data sets were collected in dark-adapted conditions. We estimate that the occupancy of the Q B site is 80% with a proximal: distal ratio of 4:1 in frozen RC crystals. We could not separate the effect of freezing from the effect of the cryoprotectants ethylene glycol or glycerol. These results could have far-reaching implications in structure/function studies of electron transfer in the acceptor quinone complex because the above are the most commonly used cryoprotectants in spectroscopic experiments.

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“…It is bound in the proximal position in RCs carrying the A(M260)W mutation close to Q A [20], the E(L212)A-D(L213)A mutations near Q B [15], and the P(L209)Y mutation that is 9…”

Section: Introductionmentioning

confidence: 99%

Temperature and cryoprotectant influence secondary quinone binding position in bacterial reaction centers

et al. 2004

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“…sphaeroides is known at atomic resolution (2)(3)(4). Three subunits with a total molecular weight of about 100 kDa compose these RCs.…”

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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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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“…The results are compared with the structure of the RC from a semiaerobically grown Rba. sphaeroides mutant strain AM260W of strain 2.4.1-containing spheroidenone (PDB ID code 1QOV) [10], which shows the useful enough resolution (2.1 Å resolution) of an RC which naturally contains a carotenoid. The present study (see below) shows that, within the limits of the resolutions of these structures, the reconstituted carotenoid occupies the same binding site as in the wild-type RC, adopts the same 15,15'-cis-configuration as in the wild-type RC, and has the same major interactions with the protein in the binding site as in the wild-type RC.…”

Section: Structures Of Carotenoids Incorporated Into Carotenoidless Rmentioning

confidence: 99%

“…This was followed by the determination of the structure of the RC from Rhodobacter (Rba.) sphaeroides [2][3][4][5][6][7][8][9][10][11]. Figure 1 shows the arrangement of the pigments in the RC of Rba.…”

Section: Introductionmentioning

confidence: 99%

Structures and functions of carotenoids bound to reaction centers from purple photosynthetic bacteria

Hashimoto

Fujii

Yanagi

et al. 2006

Pure and Applied Chemistry

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The photoprotective function of 15,15'-cis-carotenoids bound to the photosynthetic reaction centers (RCs) of purple bacteria has been studied using carotenoids reconstituted into carotenoidless RCs from Rhodobacter sphaeroides strain R26.1. The triplet-energy level of the carotenoid has been proposed to affect the quenching of the triplet state of special-pair bacteriochlorophyll (P). This was investigated using microsecond flash photolysis to detect the carotenoid triplets as a function of the number of conjugated double bonds, n. The carotenoid triplet signals were extracted by using singular-value decomposition (SVD) of the huge matrices data, and were confirmed for those having n = 8 to 11. This interpretation assumes that the reconstituted carotenoids occupy the same binding site in the RC. We have been able to confirm this assumption using X-ray crystallography to determine the structures of carotenoidless, wild-type carotenoid-containing, and 3,4-dihydro-spheroidene-reconstituted RCs. The X-ray study also emphasized the importance of the methoxy group of the carotenoids for binding to the RCs. Electroabsorption (Stark) spectroscopy was used to investigate the effect of the carotenoid on the electrostatic field around P. This electrostatic field changed by 10 % in the presence of the carotenoid.

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Ubiquinone Binding, Ubiquinone Exclusion, and Detailed Cofactor Conformation in a Mutant Bacterial Reaction Center

Cited by 77 publications

References 59 publications

Temperature and cryoprotectant influence secondary quinone binding position in bacterial reaction centers

Temperature and cryoprotectant influence secondary quinone binding position in bacterial reaction centers

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

Structures and functions of carotenoids bound to reaction centers from purple photosynthetic bacteria

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