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On the mechanism of ubiquinone mediated photocurrent generation by a reaction center based photocathode. BIOCHIMICA ET BIOPHYSICA ACTA-BIOENERGETICS 2016; 1857:1925-1934. [DOI: 10.1016/j.bbabio.2016.09.011] [Citation(s) in RCA: 25] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/30/2016] [Revised: 08/31/2016] [Accepted: 09/24/2016] [Indexed: 11/19/2022]
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Faries KM, Kressel LL, Dylla NP, Wander MJ, Hanson DK, Holten D, Laible PD, Kirmaier C. Optimizing multi-step B-side charge separation in photosynthetic reaction centers from Rhodobacter capsulatus. BIOCHIMICA ET BIOPHYSICA ACTA-BIOENERGETICS 2016; 1857:150-159. [DOI: 10.1016/j.bbabio.2015.11.013] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/24/2015] [Revised: 11/20/2015] [Accepted: 11/30/2015] [Indexed: 11/16/2022]
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Kressel L, Faries KM, Wander MJ, Zogzas CE, Mejdrich RJ, Hanson DK, Holten D, Laible PD, Kirmaier C. High yield of secondary B-side electron transfer in mutant Rhodobacter capsulatus reaction centers. BIOCHIMICA ET BIOPHYSICA ACTA-BIOENERGETICS 2014; 1837:1892-1903. [DOI: 10.1016/j.bbabio.2014.07.015] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/10/2014] [Revised: 07/22/2014] [Accepted: 07/26/2014] [Indexed: 10/25/2022]
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Williams JC, Allen JP. Directed Modification of Reaction Centers from Purple Bacteria. THE PURPLE PHOTOTROPHIC BACTERIA 2009. [DOI: 10.1007/978-1-4020-8815-5_18] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
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Wraight CA, Gunner MR. The Acceptor Quinones of Purple Photosynthetic Bacteria — Structure and Spectroscopy. THE PURPLE PHOTOTROPHIC BACTERIA 2009. [DOI: 10.1007/978-1-4020-8815-5_20] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
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Nabedryk E, Breton J. Coupling of electron transfer to proton uptake at the QB site of the bacterial reaction center: A perspective from FTIR difference spectroscopy. BIOCHIMICA ET BIOPHYSICA ACTA-BIOENERGETICS 2008; 1777:1229-48. [DOI: 10.1016/j.bbabio.2008.06.012] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/23/2008] [Revised: 06/26/2008] [Accepted: 06/27/2008] [Indexed: 01/09/2023]
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Pawlowicz NP, van Grondelle R, van Stokkum IHM, Breton J, Jones MR, Groot ML. Identification of the first steps in charge separation in bacterial photosynthetic reaction centers of Rhodobacter sphaeroides by ultrafast mid-infrared spectroscopy: electron transfer and protein dynamics. Biophys J 2008; 95:1268-84. [PMID: 18424493 PMCID: PMC2479572 DOI: 10.1529/biophysj.108.130880] [Citation(s) in RCA: 44] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/06/2008] [Accepted: 03/31/2008] [Indexed: 01/08/2023] Open
Abstract
Time-resolved visible pump/mid-infrared (mid-IR) probe spectroscopy in the region between 1600 and 1800 cm(-1) was used to investigate electron transfer, radical pair relaxation, and protein relaxation at room temperature in the Rhodobacter sphaeroides reaction center (RC). Wild-type RCs both with and without the quinone electron acceptor Q(A), were excited at 600 nm (nonselective excitation), 800 nm (direct excitation of the monomeric bacteriochlorophyll (BChl) cofactors), and 860 nm (direct excitation of the dimer of primary donor (P) BChls (P(L)/P(M))). The region between 1600 and 1800 cm(-1) encompasses absorption changes associated with carbonyl (C=O) stretch vibrational modes of the cofactors and protein. After photoexcitation of the RC the primary electron donor P excited singlet state (P*) decayed on a timescale of 3.7 ps to the state P(+)B(L)(-) (where B(L) is the accessory BChl electron acceptor). This is the first report of the mid-IR absorption spectrum of P(+)B(L)(-); the difference spectrum indicates that the 9-keto C=O stretch of B(L) is located around 1670-1680 cm(-1). After subsequent electron transfer to the bacteriopheophytin H(L) in approximately 1 ps, the state P(+)H(L)(-) was formed. A sequential analysis and simultaneous target analysis of the data showed a relaxation of the P(+)H(L)(-) radical pair on the approximately 20 ps timescale, accompanied by a change in the relative ratio of the P(L)(+) and P(M)(+) bands and by a minor change in the band amplitude at 1640 cm(-1) that may be tentatively ascribed to the response of an amide C=O to the radical pair formation. We conclude that the drop in free energy associated with the relaxation of P(+)H(L)(-) is due to an increased localization of the electron hole on the P(L) half of the dimer and a further consequence is a reduction in the electrical field causing the Stark shift of one or more amide C=O oscillators.
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Affiliation(s)
- Natalia P Pawlowicz
- Faculty of Sciences, Department of Physics and Astronomy, Vrije Universiteit Amsterdam, Amsterdam, The Netherlands.
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Paddock ML, Flores M, Isaacson R, Chang C, Abresch EC, Selvaduray P, Okamura MY. Trapped conformational states of semiquinone (D+*QB-*) formed by B-branch electron transfer at low temperature in Rhodobacter sphaeroides reaction centers. Biochemistry 2006; 45:14032-42. [PMID: 17115698 PMCID: PMC2259235 DOI: 10.1021/bi060854h] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
The reaction center (RC) from Rhodobacter sphaeroides captures light energy by electron transfer between quinones QA and QB, involving a conformational gating step. In this work, conformational states of D+*QB-* were trapped (80 K) and studied using EPR spectroscopy in native and mutant RCs that lack QA in which QB was reduced by the bacteriopheophytin along the B-branch. In mutant RCs frozen in the dark, a light induced EPR signal due to D+*QB-* formed in 30% of the sample with low quantum yield (0.2%-20%) and decayed in 6 s. A small signal with similar characteristics was also observed in native RCs. In contrast, the EPR signal due to D+*QB-* in mutant RCs illuminated while freezing formed in approximately 95% of the sample did not decay (tau >107 s) at 80 K (also observed in the native RC). In all samples, the observed g-values were the same (g = 2.0026), indicating that all active QB-*'s were located in a proximal conformation coupled with the nonheme Fe2+. We propose that before electron transfer at 80 K, the majority (approximately 70%) of QB, structurally located in the distal site, was not stably reducible, whereas the minority (approximately 30%) of active configurations was in the proximal site. The large difference in the lifetimes of the unrelaxed and relaxed D+*QB-* states is attributed to the relaxation of protein residues and internal water molecules that stabilize D+*QB-*. These results demonstrate energetically significant conformational changes involved in stabilizing the D+*QB-* state. The unrelaxed and relaxed states can be considered to be the initial and final states along the reaction coordinate for conformationally gated electron transfer.
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Affiliation(s)
- M L Paddock
- Department of Physics, University of California, San Diego, La Jolla, California 92093, USA.
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Lazár D. The polyphasic chlorophyll a fluorescence rise measured under high intensity of exciting light. FUNCTIONAL PLANT BIOLOGY : FPB 2006; 33:9-30. [PMID: 32689211 DOI: 10.1071/fp05095] [Citation(s) in RCA: 172] [Impact Index Per Article: 9.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/19/2005] [Accepted: 08/18/2005] [Indexed: 05/24/2023]
Abstract
Chlorophyll a fluorescence rise caused by illumination of photosynthetic samples by high intensity of exciting light, the O-J-I-P (O-I1-I2-P) transient, is reviewed here. First, basic information about chlorophyll a fluorescence is given, followed by a description of instrumental set-ups, nomenclature of the transient, and samples used for the measurements. The review mainly focuses on the explanation of particular steps of the transient based on experimental and theoretical results, published since a last review on chlorophyll a fluorescence induction [Lazár D (1999) Biochimica et Biophysica Acta 1412, 1-28]. In addition to 'old' concepts (e.g. changes in redox states of electron acceptors of photosystem II (PSII), effect of the donor side of PSII, fluorescence quenching by oxidised plastoquinone pool), 'new' approaches (e.g. electric voltage across thylakoid membranes, electron transport through the inactive branch in PSII, recombinations between PSII electron acceptors and donors, electron transport reactions after PSII, light gradient within the sample) are reviewed. The K-step, usually detected after a high-temperature stress, and other steps appearing in the transient (the H and G steps) are also discussed. Finally, some applications of the transient are also mentioned.
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Affiliation(s)
- Dušan Lazár
- Palacký University, Faculty of Science, Department of Experimental Physics, Laboratory of Biophysics, tř. Svobody 26, 771 46 Olomouc, Czech Republic. Email
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Watson AJ, Fyfe PK, Frolov D, Wakeham MC, Nabedryk E, van Grondelle R, Breton J, Jones MR. Replacement or exclusion of the B-branch bacteriopheophytin in the purple bacterial reaction centre: The HB cofactor is not required for assembly or core function of the Rhodobacter sphaeroides complex. BIOCHIMICA ET BIOPHYSICA ACTA-BIOENERGETICS 2005; 1710:34-46. [PMID: 16181607 DOI: 10.1016/j.bbabio.2005.08.005] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/12/2005] [Revised: 08/15/2005] [Accepted: 08/16/2005] [Indexed: 11/16/2022]
Abstract
All of the membrane-embedded cofactors of the purple bacterial reaction centre have well-defined functional or structural roles, with the exception of the bacteriopheophytin (H(B)) located approximately half-way across the membrane on the so-called inactive- or B-branch of cofactors. Sequence alignments indicate that this bacteriochlorin cofactor is a conserved feature of purple bacterial reaction centres, and a pheophytin is also found at this position in the Photosystem-II reaction centre. Possible structural or functional consequences of replacing the H(B) bacteriopheophytin by bacteriochlorophyll were investigated in the Rhodobacter sphaeroides reaction centre through mutagenesis of residue Leu L185 to His (LL185H). Results from absorbance spectroscopy indicated that the LL185H mutant assembled with a bacteriochlorophyll at the H(B) position, but this did not affect the capacity of the reaction centre to support photosynthetic growth, or change the kinetics of charge separation along the A-branch of cofactors. It was also found that mutation of residue Ala M149 to Trp (AM149W) caused the reaction centre to assemble without an H(B) bacteriochlorin, demonstrating that this cofactor is not required for correct assembly of the reaction centre. The absence of a cofactor at this position did not affect the capacity of the reaction centre to support photosynthetic growth, or the kinetics of A-branch electron transfer. A combination of X-ray crystallography and FTIR difference spectroscopy confirmed that the H(B) cofactor was absent in the AM149W mutant, and that this had not produced any significant disturbance of the adjacent ubiquinol reductase (Q(B)) site. The data are discussed with respect to possible functional roles of the H(B) bacteriopheophytin, and we conclude that the reason(s) for conservation of a bacteriopheophytin cofactor at this position in purple bacterial reaction centres are likely to be different from those underlying conservation of a pheophytin at the analogous position in Photosystem-II.
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Affiliation(s)
- Ashley J Watson
- Department of Biochemistry, School of Medical Sciences, University of Bristol, University Walk, Bristol, BS8 1TD, UK
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Nabedryk E, Paddock ML, Okamura MY, Breton J. An Isotope-Edited FTIR Investigation of the Role of Ser-L223 in Binding Quinone (QB) and Semiquinone (QB-) in the Reaction Center from Rhodobacter sphaeroides. Biochemistry 2005; 44:14519-27. [PMID: 16262252 DOI: 10.1021/bi051328d] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
In the photosynthetic reaction center (RC) from the purple bacterium Rhodobacter sphaeroides, proton-coupled electron-transfer reactions occur at the secondary quinone (Q(B)) site. Several nearby residues are important for both binding and redox chemistry involved in the light-induced conversion from Q(B) to quinol Q(B)H(2). Ser-L223 is one of the functionally important residues located near Q(B). To obtain information on the interaction between Ser-L223 and Q(B) and Q(B)(-), isotope-edited Q(B)(-)/Q(B) FTIR difference spectra were measured in a mutant RC in which Ser-L223 is replaced with Ala and compared to the native RC. The isotope-edited IR fingerprint spectra for the C=O [see text] and C=C [see text] modes of Q(B) (Q(B)(-)) in the mutant are essentially the same as those of the native RC. These findings indicate that highly equivalent interactions of Q(B) and Q(B)(-) with the protein occur in both native and mutant RCs. The simplest explanation of these results is that Ser-L223 is not hydrogen bonded to Q(B) or Q(B)(-) but presumably forms a hydrogen bond to a nearby acid group, preferentially Asp-L213. The rotation of the Ser OH proton from Asp-L213 to Q(B)(-) is expected to be an important step in the proton transfer to the reduced quinone. In addition, the reduced quinone remains firmly bound, indicating that other distinct hydrogen bonds are more important for stabilizing Q(B)(-). Implications on the design features of the Q(B) binding site are discussed.
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Affiliation(s)
- Eliane Nabedryk
- Service de Bioénergétique, CEA-Saclay, 91191 Gif-sur-Yvette Cedex, France.
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Wakeham MC, Jones MR. Rewiring photosynthesis: engineering wrong-way electron transfer in the purple bacterial reaction centre. Biochem Soc Trans 2005; 33:851-7. [PMID: 16042613 DOI: 10.1042/bst0330851] [Citation(s) in RCA: 39] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
The purple bacterial reaction centre uses light energy to separate charge across the cytoplasmic membrane, reducing ubiquinone and oxidizing a c-type cytochrome. The protein possesses a macroscopic structural two-fold symmetry but displays a strong functional asymmetry, with only one of two available membrane-spanning branches of cofactors (the so-called A-branch) being used to catalyse photochemical charge separation. The factors underlying this functional asymmetry have been the subject of study for many years but are still not fully understood. Site-directed mutagenesis has been partially successful in rerouting electron transfer along the normally inactive B-branch, allowing comparison of the kinetics of equivalent electron transfer reactions on the two branches. Both the primary and secondary electron transfer steps on the B-branch appear to be considerably slower than their A-branch counterparts. The effectiveness of different mutations in rerouting electron transfer along the B-branch of cofactors is discussed.
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Affiliation(s)
- M C Wakeham
- Department of Biochemistry, School of Medical Sciences, University of Bristol, University Walk, Bristol, BS8 1TD, UK
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Frolov D, Wakeham MC, Andrizhiyevskaya EG, Jones MR, van Grondelle R. Investigation of B-branch electron transfer by femtosecond time resolved spectroscopy in a Rhodobacter sphaeroides reaction centre that lacks the QA ubiquinone. BIOCHIMICA ET BIOPHYSICA ACTA-BIOENERGETICS 2005; 1707:189-98. [PMID: 15863097 DOI: 10.1016/j.bbabio.2004.12.006] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/11/2004] [Revised: 11/30/2004] [Accepted: 12/01/2004] [Indexed: 11/27/2022]
Abstract
The dynamics of electron transfer in a membrane-bound Rhodobacter sphaeroides reaction centre containing a combination of four mutations were investigated by transient absorption spectroscopy. The reaction centre, named WAAH, has a mutation that causes the reaction centre to assemble without a Q(A) ubiquinone (Ala M260 to Trp), a mutation that causes the replacement of the H(A) bacteriopheophytin with a bacteriochlorophyll (Leu M214 to His) and two mutations that remove acidic groups close to the Q(B) ubiquinone (Glu L212 to Ala and Asp L213 to Ala). Previous work has shown that the Q(B) ubiquinone is reduced by electron transfer along the so-called inactive cofactor branch (B-branch) in the WAAH reaction centre (M.C. Wakeham, M.G. Goodwin, C. McKibbin, M.R. Jones, Photo-accumulation of the P(+)Q(B)(-) radical pair state in purple bacterial reaction centres that lack the Q(A) ubiquinone, FEBS Letters 540 (2003) 234-240). In the present study the dynamics of electron transfer in the membrane-bound WAAH reaction centre were studied by femtosecond transient absorption spectroscopy, and the data analysed using a compartmental model. The analysis indicates that the yield of Q(B) reduction via the B-branch is approximately 8% in the WAAH reaction centre, consistent with results from millisecond time-scale kinetic spectroscopy. Possible contributions to this yield of the constituent mutations in the WAAH reaction centre and the membrane environment of the complex are discussed.
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Affiliation(s)
- Dmitrij Frolov
- Department of Physics and Astronomy, Free University of Amsterdam, De Boelelaan 1081, 1081 HV, Amsterdam, The Netherlands.
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