1
|
Nishikawa G, Saito K, Ishikita H. Modulation of Electron Transfer Branches by Atrazine and Triazine Herbicides in Photosynthetic Reaction Centers. Biochemistry 2024; 63:1206-1213. [PMID: 38587893 PMCID: PMC11080998 DOI: 10.1021/acs.biochem.4c00010] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/05/2024] [Revised: 03/15/2024] [Accepted: 03/28/2024] [Indexed: 04/09/2024]
Abstract
Quinone analogue molecules, functioning as herbicides, bind to the secondary quinone site, QB, in type-II photosynthetic reaction centers, including those from purple bacteria (PbRC). Here, we investigated the impact of herbicide binding on electron transfer branches, using herbicide-bound PbRC crystal structures and employing the linear Poisson-Boltzmann equation. In contrast to urea and phenolic herbicides [Fufezan, C. Biochemistry 2005, 44, 12780-12789], binding of atrazine and triazine did not cause significant changes in the redox-potential (Em) values of the primary quinone (QA) in these crystal structures. However, a slight Em difference at the bacteriopheophytin in the electron transfer inactive branch (HM) was observed between the S(-)- and R(+)-triazine-bound PbRC structures. This discrepancy is linked to variations in the protonation pattern of the tightly coupled Glu-L212 and Glu-H177 pairs, crucial components of the proton uptake pathway in native PbRC. These findings suggest the existence of a QB-mediated link between the electron transfer inactive HM and the proton uptake pathway in PbRCs.
Collapse
Affiliation(s)
- Gai Nishikawa
- Department
of Applied Chemistry, The University of
Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8654, Japan
| | - Keisuke Saito
- Department
of Applied Chemistry, The University of
Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8654, Japan
- Research
Center for Advanced Science and Technology, The University of Tokyo, 4-6-1 Komaba, Meguru-ku, Tokyo 153-8904, Japan
| | - Hiroshi Ishikita
- Department
of Applied Chemistry, The University of
Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8654, Japan
- Research
Center for Advanced Science and Technology, The University of Tokyo, 4-6-1 Komaba, Meguru-ku, Tokyo 153-8904, Japan
| |
Collapse
|
2
|
van Moort MR, Jones MR, Frese RN, Friebe VM. The Role of Electrostatic Binding Interfaces in the Performance of Bacterial Reaction Center Biophotoelectrodes. ACS SUSTAINABLE CHEMISTRY & ENGINEERING 2023; 11:3044-3051. [PMID: 36844753 PMCID: PMC9945312 DOI: 10.1021/acssuschemeng.2c06769] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 11/11/2022] [Revised: 01/21/2023] [Indexed: 06/18/2023]
Abstract
Photosynthetic reaction centers (RCs) efficiently capture and convert solar radiation into electrochemical energy. Accordingly, RCs have the potential as components in biophotovoltaics, biofuel cells, and biosensors. Recent biophotoelectrodes containing the RC from the bacterium Rhodobacter sphaeroides utilize a natural electron donor, horse heart cytochrome c (cyt c), as an electron transfer mediator with the electrode. In this system, electrostatic interfaces largely control the protein-electrode and protein-protein interactions necessary for electron transfer. However, recent studies have revealed kinetic bottlenecks in cyt-mediated electron transfer that limit biohybrid photoelectrode efficiency. Here, we seek to understand how changing protein-protein and protein-electrode interactions influence RC turnover and biophotoelectrode efficiency. The RC-cyt c binding interaction was modified by substituting interfacial RC amino acids. Substitutions Asn-M188 to Asp and Gln-L264 to Glu, which are known to produce a higher cyt-binding affinity, led to a decrease in the RC turnover frequency (TOF) at the electrode, suggesting that a decrease in cyt c dissociation was rate-limiting in these RC variants. Conversely, an Asp-M88 to Lys substitution producing a lower binding affinity had little effect on the RC TOF, suggesting that a decrease in the cyt c association rate was not a rate-limiting factor. Modulating the electrode surface with a self-assembled monolayer that oriented the cyt c to face the electrode did not affect the RC TOF, suggesting that the orientation of cyt c was also not a rate-limiting factor. Changing the ionic strength of the electrolyte solution had the most potent impact on the RC TOF, indicating that cyt c mobility was important for effective electron donation to the photo-oxidized RC. An ultimate limitation for the RC TOF was that cyt c desorbed from the electrode at ionic strengths above 120 mM, diluting its local concentration near the electrode-adsorbed RCs and resulting in poor biophotoelectrode performance. These findings will guide further tuning of these interfaces for improved performance.
Collapse
Affiliation(s)
- Milo R. van Moort
- Biophysics
of Photosynthesis, Department of Physics and Astronomy, Faculty of
Science, Vrije Universiteit Amsterdam, 1081 HV Amsterdam, The Netherlands
- LaserLaB
Amsterdam, Vrije Universiteit Amsterdam, 1081 HV Amsterdam, The Netherlands
| | - Michael R. Jones
- School
of Biochemistry, Biomedical Sciences Building, University of Bristol, University Walk, Bristol BS8 1TD, United Kingdom
| | - Raoul N. Frese
- Biophysics
of Photosynthesis, Department of Physics and Astronomy, Faculty of
Science, Vrije Universiteit Amsterdam, 1081 HV Amsterdam, The Netherlands
- LaserLaB
Amsterdam, Vrije Universiteit Amsterdam, 1081 HV Amsterdam, The Netherlands
| | - Vincent M. Friebe
- Biophysics
of Photosynthesis, Department of Physics and Astronomy, Faculty of
Science, Vrije Universiteit Amsterdam, 1081 HV Amsterdam, The Netherlands
- LaserLaB
Amsterdam, Vrije Universiteit Amsterdam, 1081 HV Amsterdam, The Netherlands
- Campus
Straubing for Biotechnology and Sustainability, Technical University of Munich, Uferstraße 53, 94315 Straubing, Germany
| |
Collapse
|
3
|
Faries KM, Kohout CE, Wang GX, Hanson DK, Holten D, Laible PD, Kirmaier C. Consequences of saturation mutagenesis of the protein ligand to the B-side monomeric bacteriochlorophyll in reaction centers from Rhodobacter capsulatus. PHOTOSYNTHESIS RESEARCH 2019; 141:273-290. [PMID: 30859455 DOI: 10.1007/s11120-019-00626-9] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/27/2018] [Accepted: 02/07/2019] [Indexed: 06/09/2023]
Abstract
In bacterial reaction centers (RCs), photon-induced initial charge separation uses an A-side bacteriochlorophyll (BChl, BA) and bacteriopheophytin (BPh, HA), while the near-mirror image B-side BB and HB cofactors are inactive. Two new sets of Rhodobacter capsulatus RC mutants were designed, both bearing substitution of all amino acids for the native histidine M180 (M-polypeptide residue 180) ligand to the core Mg ion of BB. Residues are identified that largely result in retention of a BChl in the BB site (Asp, Ser, Pro, Gln, Asn, Gly, Cys, Lys, and Thr), ones that largely harbor the Mg-free BPh in the BB site (Leu and Ile), and ones for which isolated RCs are comprised of a substantial mixture of these two RC types (Ala, Glu, Val, Met and, in one set, Arg). No protein was isolated when M180 is Trp, Tyr, Phe, or (in one set) Arg. These findings are corroborated by ground state spectra, pigment extractions, ultrafast transient absorption studies, and the yields of B-side transmembrane charge separation. The changes in coordination chemistries did not reveal an RC with sufficiently precise poising of the redox properties of the BB-site cofactor to result in a high yield of B-side electron transfer to HB. Insights are gleaned into the amino acid properties that support BChl in the BB site and into the widely observed multi-exponential decay of the excited state of the primary electron donor. The results also have direct implications for tuning free energies of the charge-separated intermediates in RCs and mimetic systems.
Collapse
Affiliation(s)
- Kaitlyn M Faries
- Department of Chemistry, Washington University, St. Louis, MO, 63130, USA
| | - Claire E Kohout
- Biosciences Division, Argonne National Laboratory, Lemont, IL, 60439, USA
| | - Grace Xiyu Wang
- Biosciences Division, Argonne National Laboratory, Lemont, IL, 60439, USA
| | - Deborah K Hanson
- Biosciences Division, Argonne National Laboratory, Lemont, IL, 60439, USA
| | - Dewey Holten
- Department of Chemistry, Washington University, St. Louis, MO, 63130, USA
| | - Philip D Laible
- Biosciences Division, Argonne National Laboratory, Lemont, IL, 60439, USA
| | - Christine Kirmaier
- Department of Chemistry, Washington University, St. Louis, MO, 63130, USA.
| |
Collapse
|
4
|
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]
|
5
|
Dylla NP, Faries KM, Wyllie RM, Swenson AM, Hanson DK, Holten D, Kirmaier C, Laible PD. Species differences in unlocking B‐side electron transfer in bacterial reaction centers. FEBS Lett 2016; 590:2515-26. [DOI: 10.1002/1873-3468.12264] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/20/2016] [Accepted: 06/13/2016] [Indexed: 11/09/2022]
Affiliation(s)
| | | | - Ryan M. Wyllie
- Biosciences Division Argonne National Laboratory Lemont IL USA
| | | | | | - Dewey Holten
- Department of Chemistry Washington University St. Louis MO USA
| | | | | |
Collapse
|
6
|
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]
|
7
|
Maróti Á, Wraight CA, Maróti P. Protonated rhodosemiquinone at the Q(B) binding site of the M265IT mutant reaction center of photosynthetic bacterium Rhodobacter sphaeroides. Biochemistry 2015; 54:2095-103. [PMID: 25760888 DOI: 10.1021/bi501553t] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
The second electron transfer from primary ubiquinone Q(A) to secondary ubiquinone Q(B) in the reaction center (RC) from Rhodobacter sphaeroides involves a protonated Q(B)(-) intermediate state whose low pK(a) makes direct observation impossible. Here, we replaced the native ubiquinone with low-potential rhodoquinone at the Q(B) binding site of the M265IT mutant RC. Because the in situ midpoint redox potential of Q(A) of this mutant was lowered approximately the same extent (≈100 mV) as that of Q(B) upon exchange of ubiquinone with low-potential rhodoquinone, the inter-quinone (Q(A) → Q(B)) electron transfer became energetically favorable. After subsequent saturating flash excitations, a period of two damped oscillations of the protonated rhodosemiquinone was observed. The Q(B)H(•) was identified by (1) the characteristic band at 420 nm of the absorption spectrum after the second flash and (2) weaker damping of the oscillation at 420 nm (due to the neutral form) than at 460 nm (attributed to the anionic form). The appearance of the neutral semiquinone was restricted to the acidic pH range, indicating a functional pK(a) of <5.5, slightly higher than that of the native ubisemiquinone (pK(a) < 4.5) at pH 7. The analysis of the pH and temperature dependencies of the rates of the second electron transfer supports the concept of the pH-dependent pK(a) of the semiquinone at the Q(B) binding site. The local electrostatic potential is severely modified by the strongly interacting neighboring acidic cluster, and the pK(a) of the semiquinone is in the middle of the pH range of the complex titration. The kinetic and thermodynamic data are discussed according to the proton-activated electron transfer mechanism combined with the pH-dependent functional pK(a) of the semiquinone at the Q(B) site of the RC.
Collapse
Affiliation(s)
| | - Colin A Wraight
- §Center for Biophysics and Computational Biology and Department of Plant Biology, University of Illinois, Urbana, Illinois 61801-3838, United States
| | | |
Collapse
|
8
|
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]
|
9
|
Saggu M, Carter B, Zhou X, Faries K, Cegelski L, Holten D, Boxer SG, Kirmaier C. Putative hydrogen bond to tyrosine M208 in photosynthetic reaction centers from Rhodobacter capsulatus significantly slows primary charge separation. J Phys Chem B 2014; 118:6721-32. [PMID: 24902471 PMCID: PMC4064694 DOI: 10.1021/jp503422c] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Abstract
![]()
Slow, ∼50
ps, P* → P+HA– electron
transfer is observed in Rhodobacter
capsulatus reaction centers (RCs) bearing the native
Tyr residue at M208 and the single amino acid change of isoleucine
at M204 to glutamic acid. The P* decay kinetics are unusually homogeneous
(single exponential) at room temperature. Comparative solid-state
NMR of [4′-13C]Tyr labeled wild-type and M204E RCs
show that the chemical shift of Tyr M208 is significantly altered
in the M204E mutant and in a manner consistent with formation of a
hydrogen bond to the Tyr M208 hydroxyl group. Models based on RC crystal
structure coordinates indicate that if such a hydrogen bond is formed
between the Glu at M204 and the M208 Tyr hydroxyl group, the −OH
would be oriented in a fashion expected (based on the calculations
by Alden et al., J. Phys. Chem.1996, 100, 16761–16770) to destabilize P+BA– in free energy. Alteration
of the environment of Tyr M208 and BA by Glu M204 via this
putative hydrogen bond has a powerful influence on primary charge
separation.
Collapse
Affiliation(s)
- Miguel Saggu
- Department of Chemistry, Stanford University , Stanford, California 94305-5012, United States
| | | | | | | | | | | | | | | |
Collapse
|
10
|
Vasilieva LG, Fufina TY, Gabdulkhakov AG, Leonova MM, Khatypov RA, Shuvalov VA. The site-directed mutation I(L177)H in Rhodobacter sphaeroides reaction center affects coordination of P(A) and B(B) bacteriochlorophylls. BIOCHIMICA ET BIOPHYSICA ACTA-BIOENERGETICS 2012; 1817:1407-17. [PMID: 22365928 DOI: 10.1016/j.bbabio.2012.02.008] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/20/2011] [Revised: 01/30/2012] [Accepted: 02/08/2012] [Indexed: 11/18/2022]
Abstract
To explore the influence of the I(L177)H single mutation on the properties of the nearest bacteriochlorophylls (BChls), three reaction centers (RCs) bearing double mutations were constructed in the photosynthetic purple bacterium Rhodobacter sphaeroides, and their properties and pigment content were compared with those of the correspondent single mutant RCs. Each pair of the mutations comprised the amino acid substitution I(L177)H and another mutation altering histidine ligand of BChl P(A) or BChl B(B). Contrary to expectations, the double mutation I(L177)H+H(L173)L does not bring about a heterodimer RC but causes a 46nm blue shift of the long-wavelength P absorbance band. The histidine L177 or a water molecule were suggested as putative ligands for P(A) in the RC I(L177)H+H(L173)L although this would imply a reorientation of the His backbone and additional rearrangements in the primary donor environment or even a repositioning of the BChl dimer. The crystal structure of the mutant I(L177)H reaction center determined to a resolution of 2.9Å shows changes at the interface region between the BChl P(A) and the monomeric BChl B(B). Spectral and pigment analysis provided evidence for β-coordination of the BChl B(B) in the double mutant RC I(L177)H+H(M182)L and for its hexacoordination in the mutant reaction center I(L177)H. Computer modeling suggests involvement of two water molecules in the β-coordination of the BChl B(B). Possible structural consequences of the L177 mutation affecting the coordination of the two BChls P(A) and B(B) are discussed. This article is part of a Special Issue entitled: Photosynthesis Research for Sustainability: from Natural to Artificial.
Collapse
Affiliation(s)
- L G Vasilieva
- Institute of Basic Biological Problems, Russian Academy of Sciences, Pushchino, Moscow, Russia
| | | | | | | | | | | |
Collapse
|
11
|
Faries KM, Kressel LL, Wander MJ, Holten D, Laible PD, Kirmaier C, Hanson DK. High throughput engineering to revitalize a vestigial electron transfer pathway in bacterial photosynthetic reaction centers. J Biol Chem 2012; 287:8507-14. [PMID: 22247556 DOI: 10.1074/jbc.m111.326447] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Photosynthetic reaction centers convert light energy into chemical energy in a series of transmembrane electron transfer reactions, each with near 100% yield. The structures of reaction centers reveal two symmetry-related branches of cofactors (denoted A and B) that are functionally asymmetric; purple bacterial reaction centers use the A pathway exclusively. Previously, site-specific mutagenesis has yielded reaction centers capable of transmembrane charge separation solely via the B branch cofactors, but the best overall electron transfer yields are still low. In an attempt to better realize the architectural and energetic factors that underlie the directionality and yields of electron transfer, sites within the protein-cofactor complex were targeted in a directed molecular evolution strategy that implements streamlined mutagenesis and high throughput spectroscopic screening. The polycistronic approach enables efficient construction and expression of a large number of variants of a heteroligomeric complex that has two intimately regulated subunits with high sequence similarity, common features of many prokaryotic and eukaryotic transmembrane protein assemblies. The strategy has succeeded in the discovery of several mutant reaction centers with increased efficiency of the B pathway; they carry multiple substitutions that have not been explored or linked using traditional approaches. This work expands our understanding of the structure-function relationships that dictate the efficiency of biological energy-conversion reactions, concepts that will aid the design of bio-inspired assemblies capable of both efficient charge separation and charge stabilization.
Collapse
Affiliation(s)
- Kaitlyn M Faries
- Department of Chemistry, Washington University, St. Louis, Missouri 63130, USA
| | | | | | | | | | | | | |
Collapse
|
12
|
Leonova MM, Fufina TY, Vasilieva LG, Shuvalov VA. Structure-function investigations of bacterial photosynthetic reaction centers. BIOCHEMISTRY (MOSCOW) 2012; 76:1465-83. [DOI: 10.1134/s0006297911130074] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
|
13
|
Gibasiewicz K, Pajzderska M, Potter JA, Fyfe PK, Dobek A, Brettel K, Jones MR. Mechanism of recombination of the P+H(A)- radical pair in mutant Rhodobacter sphaeroides reaction centers with modified free energy gaps between P+B(A)- and P+H(A)-. J Phys Chem B 2011; 115:13037-50. [PMID: 21970763 DOI: 10.1021/jp206462g] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Abstract
The kinetics of recombination of the P(+)H(A)(-) radical pair were compared in wild-type reaction centers from Rhodobacter sphaeroides and in seven mutants in which the free energy gap, ΔG, between the charge separated states P(+)B(A)(-) and P(+)H(A)(-) was either increased or decreased. Five of the mutant RCs had been described previously, and X-ray crystal structures of two newly constructed complexes were determined by X-ray crystallography. The charge recombination reaction was accelerated in all mutants with a smaller ΔG than in the wild-type, and was slowed in a mutant having a larger ΔG. The free energy difference between the state P(+)H(A)(-) and the PH(A) ground state was unaffected by most of these mutations. These observations were consistent with a model in which the P(+)H(A)(-) → PH(A) charge recombination is thermally activated and occurs via the intermediate state P(+)B(A)(-), with a mean rate related to the size of the ΔG between the states P(+)B(A)(-) and P(+)H(A)(-) and not the ΔG between P(+)H(A)(-) and the ground state. A more detailed analysis of charge recombination in the mutants showed that the kinetics of the reaction were multiexponential, and characterized by ~0.5, ~1-3, and 7-17 ns lifetimes, similar to those measured for wild-type reaction centers. The exact lifetimes and relative amplitudes of the three components were strongly modulated by the mutations. Two models were considered in order to explain the observed multiexponentiality and modulation, involving heterogeneity or relaxation of P(+)H(A)(-) states, with the latter model giving a better fit to the experimental results.
Collapse
|
14
|
Marchanka A, Savitsky A, Lubitz W, Möbius K, van Gastel M. B-Branch Electron Transfer in the Photosynthetic Reaction Center of a Rhodobacter sphaeroides Quadruple Mutant. Q- and W-Band Electron Paramagnetic Resonance Studies of Triplet and Radical-Pair Cofactor States. J Phys Chem B 2010; 114:14364-72. [DOI: 10.1021/jp1003424] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- A. Marchanka
- Max-Planck-Institut für Bioanorganische Chemie, Stiftstrasse 34-36, D-45470 Mülheim (Ruhr), Germany, Institut für Experimentalphysik, Freie Universität Berlin, Arnimallee 14, D-14195 Berlin, Germany
| | - A. Savitsky
- Max-Planck-Institut für Bioanorganische Chemie, Stiftstrasse 34-36, D-45470 Mülheim (Ruhr), Germany, Institut für Experimentalphysik, Freie Universität Berlin, Arnimallee 14, D-14195 Berlin, Germany
| | - W. Lubitz
- Max-Planck-Institut für Bioanorganische Chemie, Stiftstrasse 34-36, D-45470 Mülheim (Ruhr), Germany, Institut für Experimentalphysik, Freie Universität Berlin, Arnimallee 14, D-14195 Berlin, Germany
| | - K. Möbius
- Max-Planck-Institut für Bioanorganische Chemie, Stiftstrasse 34-36, D-45470 Mülheim (Ruhr), Germany, Institut für Experimentalphysik, Freie Universität Berlin, Arnimallee 14, D-14195 Berlin, Germany
| | - M. van Gastel
- Max-Planck-Institut für Bioanorganische Chemie, Stiftstrasse 34-36, D-45470 Mülheim (Ruhr), Germany, Institut für Experimentalphysik, Freie Universität Berlin, Arnimallee 14, D-14195 Berlin, Germany
| |
Collapse
|
15
|
Paddock ML, Flores M, Isaacson R, Shepherd JN, Okamura MY. EPR and ENDOR Investigation of Rhodosemiquinone in Bacterial Reaction Centers Formed by B-Branch Electron Transfer. APPLIED MAGNETIC RESONANCE 2010; 37:39. [PMID: 20157643 PMCID: PMC2821119 DOI: 10.1007/s00723-009-0042-2] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/28/2023]
Abstract
In photosynthetic bacteria, light-induced electron transfer takes place in a protein called the reaction center (RC) leading to the reduction of a bound ubiquinone molecule, Q(B), coupled with proton binding from solution. We used electron paramagnetic resonance (EPR) and electron-nuclear double resonance (ENDOR) to study the magnetic properties of the protonated semiquinone, an intermediate proposed to play a role in proton coupled electron transfer to Q(B). To stabilize the protonated semiquinone state, we used a ubiquinone derivative, rhodoquinone, which as a semiquinone is more easily protonated than ubisemiquinone. To reduce this low-potential quinone we used mutant RCs modified to directly reduce the quinone in the Q(B) site via B-branch electron transfer (Paddock et al. in Biochemistry 44:6920-6928, 2005). EPR and ENDOR signals were observed upon illumination of mutant RCs in the presence of rhodoquinone. The EPR signals had g values characteristic of rhodosemiquinone (g(x) = 2.0057, g(y) = 2.0048, g(z) ∼ 2.0018) at pH 9.5 and were changed at pH 4.5. The ENDOR spectrum showed couplings due to solvent exchangeable protons typical of hydrogen bonds similar to, but different from, those found for ubisemiquinone. This approach should be useful in future magnetic resonance studies of the protonated semiquinone.
Collapse
Affiliation(s)
- M. L. Paddock
- Department of Physics, University of California, San Diego, La Jolla, CA 92093, USA
| | - M. Flores
- Department of Physics, University of California, San Diego, La Jolla, CA 92093, USA, Max-Planck Institute for Bioinorganic Chemistry, Mülheim an der Ruhr, Germany
| | - R. Isaacson
- Department of Physics, University of California, San Diego, La Jolla, CA 92093, USA
| | - J. N. Shepherd
- Department of Chemistry, Gonzaga University, Spokane, WA 99258, USA
| | - M. Y. Okamura
- Department of Physics, University of California, San Diego, La Jolla, CA 92093, USA
| |
Collapse
|
16
|
Pawlowicz NP, van Stokkum IHM, Breton J, van Grondelle R, Jones MR. Identification of the intermediate charge-separated state P+betaL- in a leucine M214 to histidine mutant of the Rhodobacter sphaeroides reaction center using femtosecond midinfrared spectroscopy. Biophys J 2009; 96:4956-65. [PMID: 19527655 DOI: 10.1016/j.bpj.2009.03.031] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/11/2009] [Revised: 03/25/2009] [Accepted: 03/27/2009] [Indexed: 11/27/2022] Open
Abstract
Energy and electron transfer in a Leu M214 to His (LM214H) mutant of the Rhodobacter sphaeroides reaction center (RC) were investigated by applying time-resolved visible pump/midinfrared probe spectroscopy at room temperature. This mutant replacement of the Leu at position M214 resulted in the incorporation of a bacteriochlorophyll (BChl) in place of the native bacteriopheophytin in the L-branch of cofactors (denoted betaL). Purified LM214H RCs were excited at 600 nm (unselective excitation), at 800 nm (direct excitation of the monomeric BChl cofactors B(L) and B(M)), and at 860 nm (direct excitation of the primary donor (P) BChl pair (P(L)/P(M))). Absorption changes associated with carbonyl (C=O) stretch vibrational modes (9-keto, 10a-ester, and 2a-acetyl) of the cofactors and of the protein were recorded in the region between 1600 cm(-1) and 1770 cm(-1), and the data were subjected to both a sequential analysis and a simultaneous target analysis. After photoexcitation of the LM214H RC, P* decayed on a timescale of approximately 6.3 ps to P+BL-. The decay of P+BL- occurred with a lifetime of approximately 2 ps, approximately 3 times slower than that observed in wild-type and R-26 RCs (approximately 0.7 ps). Further electron transfer to the betaL BChl resulted in formation of the P+betaL- state, and its infrared absorbance difference spectrum is reported for the first time, to our knowledge. The fs midinfrared spectra of P+BL- and P+betaL- showed clear differences related to the different environments of the two BChls in the mutant RC.
Collapse
Affiliation(s)
- Natalia P Pawlowicz
- Faculty of Sciences, Department of Physics and Astronomy, Vrije Universiteit Amsterdam, Amsterdam, The Netherlands.
| | | | | | | | | |
Collapse
|
17
|
Silvennoinen L, Sandalova T, Schneider G. The polyketide cyclase RemF from Streptomyces resistomycificus
contains an unusual octahedral zinc binding site. FEBS Lett 2009; 583:2917-21. [DOI: 10.1016/j.febslet.2009.07.061] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/16/2009] [Revised: 07/30/2009] [Accepted: 07/30/2009] [Indexed: 11/28/2022]
|
18
|
Electron transfer in the Rhodobacter sphaeroides reaction center assembled with zinc bacteriochlorophyll. Proc Natl Acad Sci U S A 2009; 106:8537-42. [PMID: 19439660 DOI: 10.1073/pnas.0812719106] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
The cofactor composition and electron-transfer kinetics of the reaction center (RC) from a magnesium chelatase (bchD) mutant of Rhodobacter sphaeroides were characterized. In this RC, the special pair (P) and accessory (B) bacteriochlorophyll (BChl) -binding sites contain Zn-BChl rather than BChl a. Spectroscopic measurements reveal that Zn-BChl also occupies the H sites that are normally occupied by bacteriopheophytin in wild type, and at least 1 of these Zn-BChl molecules is involved in electron transfer in intact Zn-RCs with an efficiency of >95% of the wild-type RC. The absorption spectrum of this Zn-containing RC in the near-infrared region associated with P and B is shifted from 865 to 855 nm and from 802 to 794 nm respectively, compared with wild type. The bands of P and B in the visible region are centered at 600 nm, similar to those of wild type, whereas the H-cofactors have a band at 560 nm, which is a spectral signature of monomeric Zn-BChl in organic solvent. The Zn-BChl H-cofactor spectral differences compared with the P and B positions in the visible region are proposed to be due to a difference in the 5th ligand coordinating the Zn. We suggest that this coordination is a key feature of protein-cofactor interactions, which significantly contributes to the redox midpoint potential of H and the formation of the charge-separated state, and provides a unifying explanation for the properties of the primary acceptor in photosystems I (PS1) and II (PS2).
Collapse
|
19
|
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]
|
20
|
Jones MR. Structural Plasticity of Reaction Centers from Purple Bacteria. THE PURPLE PHOTOTROPHIC BACTERIA 2009. [DOI: 10.1007/978-1-4020-8815-5_16] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
|
21
|
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]
|
22
|
Marchanka A, Paddock M, Lubitz W, van Gastel M. Low-temperature pulsed EPR study at 34 GHz of the triplet states of the primary electron Donor P865 and the carotenoid in native and mutant bacterial reaction centers of Rhodobacter sphaeroides. Biochemistry 2007; 46:14782-94. [PMID: 18052205 DOI: 10.1021/bi701593r] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
The photosynthetic charge separation in bacterial reaction centers occurs predominantly along one of two nearly symmetric branches of cofactors. Low-temperature EPR spectra of the triplet states of the chlorophyll and carotenoid pigments in the reaction center of Rhodobacter sphaeroides R-26.1, 2.4.1 and two double-mutants GD(M203)/AW(M260) and LH(M214)/AW(M260) have been recorded at 34 GHz to investigate the relative activities of the "A" and "B" branches. The triplet states are found to derive from radical pair and intersystem crossing mechanisms, and the rates of formation are anisotropic. The former mechanism is operative for Rb. sphaeroides R-26.1, 2.4.1, and mutant GD(M203)/AW(M260) and indicates that A-branch charge separation proceeds at temperatures down to 10 K. The latter mechanism, derived from the spin polarization and operative for mutant LH(M214)/AW(M260), indicates that no long-lived radical pairs are formed upon direct excitation of the primary donor and that virtually no charge separation at the B-branch occurs at low temperatures. When the temperature is raised above 30 K, B-branch charge separation is observed, which is at most 1% of A-branch charge separation. B-branch radical pair formation can be induced at 10 K with low yield by direct excitation of the bacteriopheophytin of the B-branch at 590 nm. The formation of a carotenoid triplet state is observed. The rate of formation depends on the orientation of the reaction center in the magnetic field and is caused by a magnetic field dependence of the oscillation frequency by which the singlet and triplet radical pair precursor states interchange. Combination of these findings with literature data provides strong evidence that the thermally activated transfer step on the B-branch occurs between the primary donor, P865, and the accessory bacteriochlorophyll, whereas this step is barrierless down to 10 K along the A-branch.
Collapse
Affiliation(s)
- Aliaksandr Marchanka
- Max-Planck-Institut für Bioanorganische Chemie, P.O. Box 101365, D-45413 Mülheim an der Ruhr, Germany
| | | | | | | |
Collapse
|
23
|
Paddock ML, Flores M, Isaacson R, Chang C, Abresch EC, Okamura MY. ENDOR spectroscopy reveals light induced movement of the H-bond from Ser-L223 upon forming the semiquinone (Q(B)(-)(*)) in reaction centers from Rhodobacter sphaeroides. Biochemistry 2007; 46:8234-43. [PMID: 17590017 PMCID: PMC2597558 DOI: 10.1021/bi7005256] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Proton ENDOR spectroscopy was used to monitor local conformational changes in bacterial reaction centers (RC) associated with the electron-transfer reaction DQB --> D+*QB-* using mutant RCs capable of photoreducing QB at cryogenic temperatures. The charge separated state D+*QB-* was studied in mutant RCs formed by either (i) illuminating at low temperature (77 K) a sample frozen in the dark (ground state protein conformation) or (ii) illuminating at room temperature prior to and during freezing (charge separated state protein conformation). The charge recombination rates from the two states differed greatly (>10(6) fold) as shown previously, indicating a structural change (Paddock et al. (2006) Biochemistry 45, 14032-14042). ENDOR spectra of QB-* from both samples (35 GHz, 77 K) showed several H-bond hyperfine couplings that were similar to those for QB-* in native RCs indicating that in all RCs, QB-* was located at the proximal position near the metal site. In contrast, one set of hyperfine couplings were not observed in the dark frozen samples but were observed only in samples frozen under illumination in which the protein can relax prior to freezing. This flexible H-bond was assigned to an interaction between the Ser-L223 hydroxyl and QB-* on the basis of its absence in Ser L223 --> Ala mutant RCs. Thus, part of the protein relaxation, in response to light induced charge separation, involves the formation of an H-bond between the OH group of Ser-L223 and the anionic semiquinone QB-*. These results show the flexibility of the Ser-L223 H-bond, which is essential for its function in proton transfer to reduced QB.
Collapse
Affiliation(s)
- M L Paddock
- Department of Physics, University of California, San Diego, La Jolla, California 92093, USA.
| | | | | | | | | | | |
Collapse
|
24
|
Paddock ML, Isaacson RA, Abresch EC, Okamura MY. Light induced EPR spectra of reaction centers from Rhodobacter sphaeroides at 80K: Evidence for reduction of Q(B) by B-branch electron transfer in native reaction centers. APPLIED MAGNETIC RESONANCE 2007; 31:29-43. [PMID: 18163156 PMCID: PMC2156152 DOI: 10.1007/bf03166246] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/25/2023]
Abstract
Photosynthetic reaction centers (RCs) from Rhodobacter sphaeroides capture solar energy by electron transfer from primary donor, D, to quinone acceptor, Q(B,) through the active A-branch of electron acceptors, but not the inactive B-branch. The light induced EPR spectrum from native RCs that had Fe(2+) replaced by Zn(2+) was investigated at cryogenic temperature (80K, 35 GHz). In addition to the light induced signal due to formation of D(+•)Q(A) (-•) observed previously, a small fraction (~5%) of the signal displayed very different characteristics: (1) The signal was absent in RCs in which the Q(B) was displaced by the inhibitor stigmatellin. (2) Its decay time (τ=6 s) was the same as observed for D(+•)Q(B) (-•) in mutant RCs lacking Q(A,) which is significantly slower than for D(+•)Q(A) (-•) (τ=30 ms). (3) Its EPR spectrum was identical to that of D(+•)Q(B) (-•). (4) The quantum efficiency for forming the major component of the signal was the same as that found for mutant RCs lacking Q(A) (Φ =0.2%) and was temperature independent. These results are explained by direct photochemical reduction of Q(B)via B-branch electron transfer in a small fraction of native RCs.
Collapse
Affiliation(s)
| | | | | | - M. Y. Okamura
- Corresponding Author: Melvin Okamura, Institution: Department of Physics, University of California, San Diego, La Jolla, CA 92093-0354 USA, e-mail:
| |
Collapse
|
25
|
Jortner J. Conditions for the emergence of life on the early Earth: summary and reflections. Philos Trans R Soc Lond B Biol Sci 2006; 361:1877-91. [PMID: 17008225 PMCID: PMC1664691 DOI: 10.1098/rstb.2006.1909] [Citation(s) in RCA: 42] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
This review attempts to situate the emergence of life on the early Earth within the scientific issues of the operational and mechanistic description of life, the conditions and constraints of prebiotic chemistry, together with bottom-up molecular fabrication and biomolecular nanofabrication and top-down miniaturization approaches to the origin of terrestrial life.
Collapse
Affiliation(s)
- Joshua Jortner
- School of Chemistry, Tel Aviv University, Ramat Aviv, 69978 Tel Aviv, Israel.
| |
Collapse
|
26
|
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.
Collapse
Affiliation(s)
- M L Paddock
- Department of Physics, University of California, San Diego, La Jolla, California 92093, USA.
| | | | | | | | | | | | | |
Collapse
|
27
|
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.
Collapse
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
| |
Collapse
|