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Castell C, Rodríguez-Lumbreras LA, Hervás M, Fernández-Recio J, Navarro JA. New Insights into the Evolution of the Electron Transfer from Cytochrome f to Photosystem I in the Green and Red Branches of Photosynthetic Eukaryotes. PLANT & CELL PHYSIOLOGY 2021; 62:1082-1093. [PMID: 33772595 PMCID: PMC8557733 DOI: 10.1093/pcp/pcab044] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/10/2021] [Accepted: 03/15/2021] [Indexed: 05/11/2023]
Abstract
In cyanobacteria and most green algae of the eukaryotic green lineage, the copper-protein plastocyanin (Pc) alternatively replaces the heme-protein cytochrome c6 (Cc6) as the soluble electron carrier from cytochrome f (Cf) to photosystem I (PSI). The functional and structural equivalence of 'green' Pc and Cc6 has been well established, representing an example of convergent evolution of two unrelated proteins. However, plants only produce Pc, despite having evolved from green algae. On the other hand, Cc6 is the only soluble donor available in most species of the red lineage of photosynthetic organisms, which includes, among others, red algae and diatoms. Interestingly, Pc genes have been identified in oceanic diatoms, probably acquired by horizontal gene transfer from green algae. However, the mechanisms that regulate the expression of a functional Pc in diatoms are still unclear. In the green eukaryotic lineage, the transfer of electrons from Cf to PSI has been characterized in depth. The conclusion is that in the green lineage, this process involves strong electrostatic interactions between partners, which ensure a high affinity and an efficient electron transfer (ET) at the cost of limiting the turnover of the process. In the red lineage, recent kinetic and structural modeling data suggest a different strategy, based on weaker electrostatic interactions between partners, with lower affinity and less efficient ET, but favoring instead the protein exchange and the turnover of the process. Finally, in diatoms the interaction of the acquired green-type Pc with both Cf and PSI may not yet be optimized.
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Affiliation(s)
- Carmen Castell
- Instituto de Bioquímica Vegetal y Fotosíntesis, CSIC and Universidad de Sevilla, cicCartuja, Sevilla, Spain
| | - Luis A Rodríguez-Lumbreras
- Instituto de Ciencias de la Vid y del Vino (ICVV), CSIC—Universidad de La Rioja—Gobierno de La Rioja, Logroño, Spain
| | - Manuel Hervás
- Instituto de Bioquímica Vegetal y Fotosíntesis, CSIC and Universidad de Sevilla, cicCartuja, Sevilla, Spain
| | - Juan Fernández-Recio
- Instituto de Ciencias de la Vid y del Vino (ICVV), CSIC—Universidad de La Rioja—Gobierno de La Rioja, Logroño, Spain
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Malone LA, Proctor MS, Hitchcock A, Hunter CN, Johnson MP. Cytochrome b 6f - Orchestrator of photosynthetic electron transfer. BIOCHIMICA ET BIOPHYSICA ACTA-BIOENERGETICS 2021; 1862:148380. [PMID: 33460588 DOI: 10.1016/j.bbabio.2021.148380] [Citation(s) in RCA: 51] [Impact Index Per Article: 17.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Subscribe] [Scholar Register] [Received: 10/08/2020] [Revised: 01/06/2021] [Accepted: 01/09/2021] [Indexed: 11/18/2022]
Abstract
Cytochrome b6f (cytb6f) lies at the heart of the light-dependent reactions of oxygenic photosynthesis, where it serves as a link between photosystem II (PSII) and photosystem I (PSI) through the oxidation and reduction of the electron carriers plastoquinol (PQH2) and plastocyanin (Pc). A mechanism of electron bifurcation, known as the Q-cycle, couples electron transfer to the generation of a transmembrane proton gradient for ATP synthesis. Cytb6f catalyses the rate-limiting step in linear electron transfer (LET), is pivotal for cyclic electron transfer (CET) and plays a key role as a redox-sensing hub involved in the regulation of light-harvesting, electron transfer and photosynthetic gene expression. Together, these characteristics make cytb6f a judicious target for genetic manipulation to enhance photosynthetic yield, a strategy which already shows promise. In this review we will outline the structure and function of cytb6f with a particular focus on new insights provided by the recent high-resolution map of the complex from Spinach.
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Affiliation(s)
- Lorna A Malone
- Department of Molecular Biology and Biotechnology, University of Sheffield, Sheffield S10 2TN, UK
| | - Matthew S Proctor
- Department of Molecular Biology and Biotechnology, University of Sheffield, Sheffield S10 2TN, UK
| | - Andrew Hitchcock
- Department of Molecular Biology and Biotechnology, University of Sheffield, Sheffield S10 2TN, UK
| | - C Neil Hunter
- Department of Molecular Biology and Biotechnology, University of Sheffield, Sheffield S10 2TN, UK
| | - Matthew P Johnson
- Department of Molecular Biology and Biotechnology, University of Sheffield, Sheffield S10 2TN, UK.
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3
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Single-molecule study of redox control involved in establishing the spinach plastocyanin-cytochrome bf electron transfer complex. BIOCHIMICA ET BIOPHYSICA ACTA-BIOENERGETICS 2019; 1860:591-599. [DOI: 10.1016/j.bbabio.2019.06.013] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/01/2019] [Revised: 06/18/2019] [Accepted: 06/21/2019] [Indexed: 01/06/2023]
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4
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Subunit interactions as mediated by “non-interface” residues in living cells for multiple homo-oligomeric proteins. Biochem Biophys Res Commun 2019; 512:100-105. [DOI: 10.1016/j.bbrc.2019.03.004] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/23/2019] [Accepted: 03/01/2019] [Indexed: 11/22/2022]
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Owens CP, Katz FEH, Carter CH, Luca MA, Tezcan FA. Evidence for Functionally Relevant Encounter Complexes in Nitrogenase Catalysis. J Am Chem Soc 2015; 137:12704-12. [PMID: 26360912 PMCID: PMC4809638 DOI: 10.1021/jacs.5b08310] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
Nitrogenase is the only enzyme that can convert atmospheric dinitrogen (N2) into biologically usable ammonia (NH3). To achieve this multielectron redox process, the nitrogenase component proteins, MoFe-protein (MoFeP) and Fe-protein (FeP), repeatedly associate and dissociate in an ATP-dependent manner, where one electron is transferred from FeP to MoFeP per association. Here, we provide experimental evidence that encounter complexes between FeP and MoFeP play a functional role in nitrogenase catalysis. The encounter complexes are stabilized by electrostatic interactions involving a positively charged patch on the β-subunit of MoFeP. Three single mutations (βAsn399Glu, βLys400Glu, and βArg401Glu) in this patch were generated in Azotobacter vinelandii MoFeP. All of the resulting variants displayed decreases in specific catalytic activity, with the βK400E mutation showing the largest effect. As simulated by the Thorneley-Lowe kinetic scheme, this single mutation lowered the rate constant for FeP-MoFeP association 5-fold. We also found that the βK400E mutation did not affect the coupling of ATP hydrolysis with electron transfer (ET) between FeP and MoFeP. These data suggest a mechanism where FeP initially forms encounter complexes on the MoFeP β-subunit surface en route to the ATP-activated, ET-competent complex over the αβ-interface.
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Affiliation(s)
- Cedric P. Owens
- Department of Chemistry and Biochemistry, University of California, San Diego, La Jolla, California, 92039, United States
| | - Faith E. H. Katz
- Department of Chemistry and Biochemistry, University of California, San Diego, La Jolla, California, 92039, United States
| | - Cole H. Carter
- Department of Chemistry and Biochemistry, University of California, San Diego, La Jolla, California, 92039, United States
| | - Maria A. Luca
- Department of Chemistry and Biochemistry, University of California, San Diego, La Jolla, California, 92039, United States
| | - F. Akif Tezcan
- Department of Chemistry and Biochemistry, University of California, San Diego, La Jolla, California, 92039, United States
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Khruschev SS, Abaturova AM, Diakonova AN, Fedorov VA, Ustinin DM, Kovalenko IB, Riznichenko GY, Rubin AB. Brownian-dynamics simulations of protein–protein interactions in the photosynthetic electron transport chain. Biophysics (Nagoya-shi) 2015. [DOI: 10.1134/s0006350915020086] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022] Open
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7
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Feng H, Zhang Q, Wang Q, Wang X, Liu J, Li M, Huang L, Kang Z. Target of tae-miR408, a chemocyanin-like protein gene (TaCLP1), plays positive roles in wheat response to high-salinity, heavy cupric stress and stripe rust. PLANT MOLECULAR BIOLOGY 2013; 83:433-43. [PMID: 23864359 DOI: 10.1007/s11103-013-0101-9] [Citation(s) in RCA: 70] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/03/2013] [Accepted: 06/25/2013] [Indexed: 05/18/2023]
Abstract
microRNAs (miRNAs) are novel and significant regulators of gene expression at the post-transcriptional level, and they are essential for normal growth and development and adaptation to stress conditions. As miRNAs are a kind of RNAs that do not code proteins, they play roles by repressing gene translation or degrading the corresponding target mRNAs. Plantacyanin-like (basic blue) proteins have been predicted and verified as the target gene of miR408 in wheat and Arabidopsis, respectively. Besides some biochemical characteristics, their detailed biological function remains unknown. In this study, the target gene of a wheat miRNA (tae-miR408), designated TaCLP1, was identified using degradome sequencing and co-transformation technology in tobacco leaves. We isolated the full-length cDNA clone, and defined its product as a chemocyanin-like protein, a kind of plantacyanin. Transcript accumulation of TaCLP1 and tae-miR408 showed contrasting divergent expression patterns in wheat response to Puccinia striiformis f. sp. tritici (Pst) and high copper ion stress. Overexpression of TaCLP1 in yeast (Schizosaccharomyces pombe) significantly increased cell growth under high salinity and Cu²⁺ stresses. Silencing of individual cDNA clones in wheat challenged with Pst indicated that TaCLP1 positively regulates resistance to stripe rust. The results indicate that the target of tae-miR408, TaCLP1, play an important role in regulating resistance of host plants to abiotic stresses and stripe rust, and such interactions can be a valuable resource for investigating stress tolerance in wheat.
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Affiliation(s)
- Hao Feng
- State Key Laboratory of Crop Stress Biology for Arid Areas and College of Plant Protection, Northwest A&F University, Yangling, Shaanxi, 712100, People's Republic of China
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Kaas Q, Craik DJ. NMR of plant proteins. PROGRESS IN NUCLEAR MAGNETIC RESONANCE SPECTROSCOPY 2013; 71:1-34. [PMID: 23611313 DOI: 10.1016/j.pnmrs.2013.01.003] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/02/2013] [Accepted: 01/21/2013] [Indexed: 06/02/2023]
Affiliation(s)
- Quentin Kaas
- The University of Queensland, Institute for Molecular Bioscience, Brisbane, Queensland 4072, Australia
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Simultaneous true, gated, and coupled electron-transfer reactions and energetics of protein rearrangement. J Inorg Biochem 2012; 106:143-50. [DOI: 10.1016/j.jinorgbio.2011.09.017] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/11/2011] [Revised: 09/06/2011] [Accepted: 09/09/2011] [Indexed: 11/19/2022]
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10
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Churbanova IY, Poulos TL, Sevrioukova IF. Production and characterization of a functional putidaredoxin reductase-putidaredoxin covalent complex. Biochemistry 2010; 49:58-67. [PMID: 19954240 DOI: 10.1021/bi901872s] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
In the cytochrome P450cam-dependent monooxygenase system from Pseudomonas putida, putidaredoxin (Pdx) shuttles electrons between putidaredoxin reductase (Pdr) and P450cam and, thus, must form transient complexes with both partners. 1-Ethyl 3-[3-(dimethylamino)propyl]carbodiimide (EDC) was found to promote formation of stoichiometric Pdr-Pdx complexes only when carboxyl groups on Pdx were activated. The yield of the EDC-mediated cross-link depended on the Pdx variant used and the redox state of both partners, decreasing in the following order: Pdr(ox)-Pdx(ox) > Pdr(ox)-Pdx(red) > or = Pdr(red)-Pdx(red). The Pdr-Pdx C73S/C85S conjugate was purified and characterized. Compared to the equimolar mixture of intact Pdr and Pdx, the fusion protein was more efficient in electron transfer to cytochrome c and, in the presence of saturating levels of P450cam, more effectively supported camphor hydroxylation. On the basis of our results, we conclude that (i) the cross-linked complex is physiologically relevant and represents a suitable model for mechanistic studies, (ii) molecular recognition between Pdr and Pdx is redox-controlled and assisted by the Glu72(Pdx)-Lys409(Pdr) charge-charge interactions, and (iii) the high specificity of the Pdr-Pdx couple may be due to finely tuned interactions at the protein-protein interface resulting in only one strongly preferred docking orientation leading to efficient FAD-to-[2Fe-2S] electron transfer.
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Affiliation(s)
- Inna Y Churbanova
- Department of Molecular Biology, University of California, Irvine, California 92697-3900, USA
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11
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The courtship of proteins: Understanding the encounter complex. FEBS Lett 2009; 583:1060-6. [DOI: 10.1016/j.febslet.2009.02.046] [Citation(s) in RCA: 147] [Impact Index Per Article: 9.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/26/2009] [Revised: 02/25/2009] [Accepted: 02/27/2009] [Indexed: 11/15/2022]
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12
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Gursahani S, Schoephoerster RT, Prabhakaran M. Exploring Electron Transfer Between Heme Proteins of Cytochrome c Super Family in Biosensors: A Molecular Mechanics Study. J Biomol Struct Dyn 2008; 26:329-38. [DOI: 10.1080/07391102.2008.10507248] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/28/2022]
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13
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Shi X, Duft D, Parks JH. Fluorescence Quenching Induced by Conformational Fluctuations in Unsolvated Polypeptides. J Phys Chem B 2008; 112:12801-15. [DOI: 10.1021/jp8033598] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Xiangguo Shi
- The Rowland Institute at Harvard, 100 Edwin H. Land Boulevard, Cambridge, Massachusetts 02142
| | - Denis Duft
- The Rowland Institute at Harvard, 100 Edwin H. Land Boulevard, Cambridge, Massachusetts 02142
| | - Joel H Parks
- The Rowland Institute at Harvard, 100 Edwin H. Land Boulevard, Cambridge, Massachusetts 02142
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14
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Ullmann GM, Kloppmann E, Essigke T, Krammer EM, Klingen AR, Becker T, Bombarda E. Investigating the mechanisms of photosynthetic proteins using continuum electrostatics. PHOTOSYNTHESIS RESEARCH 2008; 97:33-53. [PMID: 18478354 DOI: 10.1007/s11120-008-9306-1] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/01/2007] [Accepted: 04/10/2008] [Indexed: 05/26/2023]
Abstract
Computational methods based on continuum electrostatics are widely used in theoretical biochemistry to analyze the function of proteins. Continuum electrostatic methods in combination with quantum chemical and molecular mechanical methods can help to analyze even very complex biochemical systems. In this article, applications of these methods to proteins involved in photosynthesis are reviewed. After giving a short introduction to the basic concepts of the continuum electrostatic model based on the Poisson-Boltzmann equation, we describe the application of this approach to the docking of electron transfer proteins, to the comparison of isofunctional proteins, to the tuning of absorption spectra, to the analysis of the coupling of electron and proton transfer, to the analysis of the effect of membrane potentials on the energetics of membrane proteins, and to the kinetics of charge transfer reactions. Simulations as those reviewed in this article help to analyze molecular mechanisms on the basis of the structure of the protein, guide new experiments, and provide a better and deeper understanding of protein functions.
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Affiliation(s)
- G Matthias Ullmann
- Structural Biology/Bioinformatics, University of Bayreuth, Universitätsstr. 30, BGI, Bayreuth 95447, Germany.
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15
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Anula HM, Myshkin E, Guliaev A, Luman C, Danilov EO, Castellano FN, Bullerjahn GS, Rodgers MAJ. Photo Processes on Self-Associated Cationic Porphyrins and Plastocyanin Complexes 1. Ligation of Plastocyanin Tyrosine 83 onto Metalloporphyrins and Electron-Transfer Fluorescence Quenching. J Phys Chem A 2006; 110:2545-59. [PMID: 16480316 DOI: 10.1021/jp054712t] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
The spectroscopic properties of the self-associated complexes formed between the anionic surface docking site of spinach plastocyanin and the cationic metalloporphyrins, in which the tyrosine 83 (Y83) moiety is placed just below the docking site, tetrakis(N-methyl-4-pyridyl)porphyrin (Pd(II)TMPyP(4+) and Zn(II)TMPyP(4+)), have been studied and reported herein. The fluorescence quenching phenomenon of the self-assembled complex of Zn(II)TMPyP(4+)/plastocyanin has also been discovered. The observed red-shifting of the Soret and Q-bands of the UV-visible spectra, ca. 9 nm for Pd(II)TMPyP(4+)/plastocyanin and ca. 6 nm for the Zn(II)TMPyP(4+)/plastocyanin complexes, was explained in terms of exciton theory coupled with the Gouterman model. Thus, the hydroxyphenyl terminus of the Y83 residue of the self-associated plastocyanin/cationic porphyrin complexes was implicated in the charge-transfer ligation with the central metal atoms of these metalloporphyrins. Moreover, ground-state spectrometric-binding studies between Pd(II)TMPyP(4+) and the Y83 mutant plastocyanin (Y83F-PC) system proved that Y83 moiety of plastocyanin played a critical role in the formation of such ion-pair complexes. Difference absorption spectra and the Job's plots showed that the electrostatic attractions between the cationic porphyrins and the anionic patch of plastocyanin, bearing the nearby Y83 residue, led to the predominant formation of a self-associated 1:1 complex in the ground-state with significantly high binding constants (K = (8.0 +/- 1.1) x 10(5) M(-1) and (2.7 +/- 0.8) x 10(6) M(-1) for Pd(II)TMPyP(4+) and zinc variant, respectively) in low ionic strength buffer, 1 mM KCl and 1 mM phosphate buffer (pH 7.4). Molecular modeling calculations supported the formation of a 1:1 self-associated complex between the porphyrin and plastocyanin with an average distance of ca. 9 A between the centers of mass of the porphyrin and Y83 positioned just behind the anionic surface docking site on the protein surface. The photoexcited singlet state of Zn(II)TMPyP(4+) was quenched by the Y83 residue of the self-associated plastocyanin in a static mechanism as evidenced by steady-state and time-resolved fluorescence experiments. Even when all the porphyrin was complexed (more than 97%), significant residual fluorescence from the complex was observed such that the amplitude of quenching of the singlet state of uncomplexed species was enormously obscured.
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Affiliation(s)
- Hewa M Anula
- The Center for Photochemical Sciences and Departments of Chemistry and Biological Sciences, Bowling Green State University, Bowling Green, Ohio 43403, USA
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Haddadian EJ, Gross EL. A Brownian dynamics study of the effects of cytochrome f structure and deletion of its small domain in interactions with cytochrome c6 and plastocyanin in Chlamydomonas reinhardtii. Biophys J 2006; 90:566-77. [PMID: 16239335 PMCID: PMC1367061 DOI: 10.1529/biophysj.105.067058] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/20/2005] [Accepted: 09/13/2005] [Indexed: 11/18/2022] Open
Abstract
The availability of seven different structures of cytochrome f (cyt f) from Chlamydomonas reinhardtii allowed us, using Brownian dynamics simulations, to model interactions between these molecules and their redox partners, plastocyanin (PC) and cytochrome c6 (cyt c6) in the same species to study the effect of cyt f structure on its function. Our results showed that different cyt f structures, which are very similar, produced different reaction rates in interactions with PC and cyt c6. We were able to attribute this to structural differences among these molecules, particularly to a small flexible loop between A-184 and G-191 (which has some of the highest crystallographic temperature factors in all of the cyt f structures) on the cyt f small domain. We also showed that deletion of the cyt f small domain affected cyt c6 more than PC, due to their different binding positions on cyt f. One function of the small domain in cyt f may be to guide PC or cyt c6 to a uniform dock with cyt f, especially due to electrostatic interactions with K-188 and K-189 on this domain. Our results could serve as a good guide for future experimental work on these proteins to understand better the electron transfer process between them. Also, these results demonstrated the sensitivity and the power of the Brownian dynamics simulations in the study of molecular interactions.
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Affiliation(s)
- Esmael J Haddadian
- Biophysics Program and Department of Biochemistry, The Ohio State University, Columbus, Ohio 43210, USA
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Gross EL, Rosenberg I. A Brownian dynamics study of the interaction of Phormidium cytochrome f with various cyanobacterial plastocyanins. Biophys J 2006; 90:366-80. [PMID: 16214856 PMCID: PMC1367034 DOI: 10.1529/biophysj.105.065185] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/22/2005] [Accepted: 09/13/2005] [Indexed: 11/18/2022] Open
Abstract
Brownian dynamics simulations were used to study the role of electrostatic forces in the interactions of cytochrome f from the cyanobacterium Phormidium laminosum with various cyanobacterial plastocyanins. Both the net charge on the plastocyanin molecule and the charge configuration around H92 (H87 in higher plants) are important in determining the interactions. Those plastocyanins (PCs) with a net charge more negative than -2.0, including those from Synechococcus sp. PCC7942, Synechocystis sp. 6803, and P. laminosum showed very little complex formation. On the other hand, complex formation for those with a net charge more positive than -2.0 (including Nostoc sp. PCC7119 and Prochlorothrix hollandica) as well as Nostoc plastocyanin mutants showed a linear dependence of complex formation upon the net charge on the plastocyanin molecule. Mutation of charged residues on the surface of the PC molecules also affected complex formation. Simulations involving plastocyanin mutants K35A, R93A, and K11A (when present) showed inhibition of complex formation. In contrast, D10A and E17A mutants showed an increase in complex formation. All of these residues surround the H92 (H87 in higher plant plastocyanins) ligand to the copper. An examination of the closest electrostatic contacts shows that these residues interact with D63, E123, R157, D188, and the heme on Phormidium cytochrome f. In the complexes formed, the long axis of the PC molecule lies perpendicular to the long axis of cytochrome f. There is considerable heterogeneity in the orientation of plastocyanin in the complexes formed.
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Affiliation(s)
- Elizabeth L Gross
- Department of Biochemistry, The Ohio State University, Columbus, Ohio, USA.
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Lange C, Cornvik T, Díaz-Moreno I, Ubbink M. The transient complex of poplar plastocyanin with cytochrome f: effects of ionic strength and pH. BIOCHIMICA ET BIOPHYSICA ACTA-BIOENERGETICS 2005; 1707:179-88. [PMID: 15863096 DOI: 10.1016/j.bbabio.2004.12.002] [Citation(s) in RCA: 34] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/19/2004] [Revised: 11/25/2004] [Accepted: 12/01/2004] [Indexed: 11/30/2022]
Abstract
The orientation of poplar plastocyanin in the complex with turnip cytochrome f has been determined by rigid-body calculations using restraints from paramagnetic NMR measurements. The results show that poplar plastocyanin interacts with cytochrome f with the hydrophobic patch of plastocyanin close to the heme region on cytochrome f and via electrostatic interactions between the charged patches on both proteins. Plastocyanin is tilted relative to the orientation reported for spinach plastocyanin, resulting in a longer distance between iron and copper (13.9 A). With increasing ionic strength, from 0.01 to 0.11 M, all observed chemical-shift changes decrease uniformly, supporting the idea that electrostatic forces contribute to complex formation. There is no indication for a rearrangement of the transient complex in this ionic strength range, contrary to what had been proposed earlier on the basis of kinetic data. By decreasing the pH from pH 7.7 to pH 5.5, the complex is destabilized. This may be attributed to the protonation of the conserved acidic patches or the copper ligand His87 in poplar plastocyanin, which are shown to have similar pK(a) values. The results are interpreted in a two-step model for complex formation.
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Affiliation(s)
- Christian Lange
- Leiden Institute of Chemistry, Leiden University, Gorlaeus Laboratories, P.O. Box 9502, 2300 RA Leiden, The Netherlands
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Haddadian EJ, Gross EL. Brownian dynamics study of cytochrome f interactions with cytochrome c6 and plastocyanin in Chlamydomonas reinhardtii plastocyanin, and cytochrome c6 mutants. Biophys J 2005; 88:2323-39. [PMID: 15626695 PMCID: PMC1305281 DOI: 10.1529/biophysj.104.053561] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/25/2004] [Accepted: 12/17/2004] [Indexed: 11/18/2022] Open
Abstract
Using Brownian dynamics simulations, all of the charged residues in Chlamydomonas reinhardtii cytochrome c(6) (cyt c(6)) and plastocyanin (PC) were mutated to alanine and their interactions with cytochrome f (cyt f) were modeled. Systematic mutation of charged residues on both PC and cyt c(6) confirmed that electrostatic interactions (at least in vitro) play an important role in bringing these proteins sufficiently close to cyt f to allow hydrophobic and van der Waals interactions to form the final electron transfer-active complex. The charged residue mutants on PC and cyt c(6) displayed similar inhibition classes. Our results indicate a difference between the two acidic clusters on PC. Mutations D44A and E43A of the lower cluster showed greater inhibition than do any of the mutations of the upper cluster residues. Replacement of acidic residues on cyt c(6) that correspond to the PC's lower cluster, particularly E70 and E69, was observed to be more inhibitory than those corresponding to the upper cluster. In PC residues D42, E43, D44, D53, D59, D61, and E85, and in cyt c(6) residues D2, E54, K57, D65, R66, E70, E71, and the heme had significant electrostatic contacts with cyt f charged residues. PC and cyt c(6) showed different binding sites and orientations on cyt f. As there are no experimental cyt c(6) mutation data available for algae, our results could serve as a good guide for future experimental work on this protein. The comparison between computational values and the available experimental data (for PC-cyt f interactions) showed overall good agreement, which supports the predictive power of Brownian dynamics simulations in mutagenesis studies.
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Affiliation(s)
- Esmael J Haddadian
- Biophysics Program and Department of Biochemistry, The Ohio State University, 484 W. 12th Ave., Columbus, OH 43210, USA
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Gross EL. A Brownian dynamics study of the interaction of Phormidium laminosum plastocyanin with Phormidium laminosum cytochrome f. Biophys J 2004; 87:2043-59. [PMID: 15345580 PMCID: PMC1304607 DOI: 10.1529/biophysj.103.038497] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/18/2003] [Accepted: 05/21/2004] [Indexed: 11/18/2022] Open
Abstract
The interaction of Phormidium laminosum plastocyanin (PC) with P. laminosum cytochrome f (cyt f) was studied using Brownian dynamics (BD) simulations. Few complexes and a low rate of electron transfer were observed for wild-type PC. Increasing the positive electrostatic field on PC by the addition of a Zn(2+) ion in the neighborhood of D44 and D45 on PC (as found in crystal structure of plastocyanin) increased the number of complexes formed and the calculated rates of electron transfer as did PC mutations D44A, D45A, E54A, and E57A. Mutations of charged residues on Phormidium PC and Phormidium cyt f were used to map binding sites on both proteins. In both the presence and absence of the Zn(2+) ion, the following residues on PC interact with cyt f: D44, D45, K6, D79, R93, and K100 that lie in a patch just below H92 and Y88 and D10, E17, and E70 located on the upper portion of the PC molecule. In the absence of the Zn(2+) ion, K6 and K35 on the top of the PC molecule also interact with cyt f. Cyt f residues involved in binding PC, in the absence of the Zn(2+) ion, include E165, D187, and D188 that are located on the small domain of cyt f. The orientation of PC in the complexes was quite random in accordance with NMR results. In the presence of the Zn(2+) ion, K53 and E54 in the lower patch of the PC molecule also interact with cyt f and PC interacts with E86, E95, and E123 on the large domain of cyt f. Also, the orientation of PC in the complexes was much more uniform than in the absence of the Zn(2+) ion. The difference may be due to both the larger electrostatic field and the greater asymmetry of the charge distribution on PC observed in the presence of the Zn(2+) ion. Hydrophobic interactions were also observed suggesting a model of cyt f-PC interactions in which electrostatic forces bring the two molecules together but hydrophobic interactions participate in stabilizing the final electron-transfer-active dock.
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Affiliation(s)
- Elizabeth L Gross
- Department of Biochemistry, The Ohio State University, Columbus, Ohio 34210, USA.
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21
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Crowley PB, Hunter DM, Sato K, McFarlane W, Dennison C. The parsley plastocyanin-turnip cytochrome f complex: a structurally distorted but kinetically functional acidic patch. Biochem J 2004; 378:45-51. [PMID: 14585099 PMCID: PMC1223930 DOI: 10.1042/bj20031423] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/17/2003] [Revised: 10/13/2003] [Accepted: 10/30/2003] [Indexed: 11/17/2022]
Abstract
In general, inter-protein electron transfer proceeds via the formation of transient complexes. The initial stage of the interaction between plastocyanin (PCu) and cytochrome f (cyt f ) from plants is mediated by complementary electrostatics. Given the diffuse nature of its acidic patch, parsley PCu is an atypical example of a plant PCu. The interaction of this PCu with turnip cyt f was investigated by stopped-flow kinetics, NMR spectroscopy and protein-docking simulations. We show that, despite the altered acidic patch, parsley PCu is as efficient as spinach PCu in accepting electrons from cyt f, over the physiological range of ionic strength. At high ionic strength, the rate constant for the reaction of cyt f with parsley PCu is twice that of the spinach protein. This difference in reactivity is attributed to variations in the hydrophobic patch of parsley PCu. The results of NMR studies and protein-docking simulations indicate that parsley PCu and its spinach analogue adopt different orientations in their complexes with cyt f.
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Affiliation(s)
- Peter B Crowley
- Instituto de Tecnologia Química e Biológica, Universidade Nova de Lisboa, Av. Da República, Apartado 127, 2781 901 Oeiras, Portugal
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22
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Gross EL, Pearson DC. Brownian dynamics simulations of the interaction of Chlamydomonas cytochrome f with plastocyanin and cytochrome c6. Biophys J 2003; 85:2055-68. [PMID: 12944318 PMCID: PMC1303377 DOI: 10.1016/s0006-3495(03)74633-5] [Citation(s) in RCA: 49] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/11/2002] [Accepted: 05/05/2003] [Indexed: 11/30/2022] Open
Abstract
The interaction of Chlamydomonas cytochrome f (cyt f) with either Chlamydomonas plastocyanin (PC) or Chlamydomonas cytochrome c(6) (cyt c(6)) was studied using Brownian dynamics simulations. The two electron acceptors (PC and cyt c(6)) were found to be essentially interchangeable despite a lack of sequence homology and different secondary structures (beta-sheet for PC and alpha-helix for cyt c(6)). Simulations using PC and cyt c(6) interacting with cyt f showed approximately equal numbers of successful complexes and calculated rates of electron transfer. Cyt f-PC and cyt f-cyt c(6) showed the same types of interactions. Hydrophobic residues surrounding the Y1 ligand to the heme on cyt f interacted with hydrophobic residues on PC (surrounding the H87 ligand to the Cu) or cyt c(6) (surrounding the heme). Both types of complexes were stabilized by electrostatic interactions between K65, K188, and K189 on cyt f and conserved anionic residues on PC (E43, D44, D53, and E85) or cyt c(6) (E2, E70, and E71). Mutations on cyt f had identical effects on its interaction with either PC or cyt c(6). K65A, K188A, and K189A showed the largest effects whereas residues such as K217A, R88A, and K110A, which are located far from the positive patch on cyt f, showed very little inhibition. The effect of mutations observed in Brownian dynamics simulations paralleled those observed in experiments.
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Affiliation(s)
- Elizabeth L Gross
- Department of Biochemistry and Biophysics Program, The Ohio State University, Columbus, Ohio 43210, USA.
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23
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Jeuken LJC. Conformational reorganisation in interfacial protein electron transfer. BIOCHIMICA ET BIOPHYSICA ACTA 2003; 1604:67-76. [PMID: 12765764 DOI: 10.1016/s0005-2728(03)00026-4] [Citation(s) in RCA: 69] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
Abstract
Protein-protein electron transfer (ET) plays an essential role in all redox chains. Earlier studies which used cross-linking and increased solution viscosity indicated that the rate of many ET reactions is limited (i.e., gated) by conformational reorientations at the surface interface. These results are later supported by structural studies using NMR and molecular modelling. New insights into conformational gating have also come from electrochemical experiments in which proteins are noncovalently adsorbed on the electrode surface. These systems have the advantage that it is relatively easy to vary systematically the driving force and electronic coupling. In this review we summarize the current knowledge obtained from these electrochemical experiments and compare it with some of the results obtained for protein-protein ET.
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24
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Effects of pH on kinetics of the structural rearrangement that gates the electron-transfer reaction between zinc cytochrome c and plastocyanin: Analysis of protonation states in a diprotein complex. JOURNAL OF THE SERBIAN CHEMICAL SOCIETY 2003. [DOI: 10.2298/jsc0305327c] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
Abstract
Electron transfer from zinc cytochrome c to copper(II)plastocyanin in the electrostatically- stabilized complex [Crnogorac MM, Shen C, Young S Hansson O, Kostic NM (1996) Biochemistry 35, 16465?74]. We study this rearrangement in four complexes Zncyt/pc(II), which zinc cytochrome c makes with the wild-type form and the single mutants Asp42Asn, Glu59Gln, and Glu60Gln of plastocyanin. The rate constant for the rearrangement, kF differs for the four forms of plastocyanin but is independent of pH from 5.4 to 9.0 in all four cases. That kF is affected by the single mutations but not by pH changes suggests that the residues Asp 42, Glu59, and Glu60 in the wild-type plastocyanin remain deprotonated (i.e., as anions) within the Zncyt/pc(II) complex throughout the pH range examined. This fact agrees with the notion that loss of salt bridges in the initial (redox-inactive) configuration of the complex is compensated by formation of new salt bridges in the rearranged (redox-active) configuration.
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25
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Hirota S, Yamauchi O. Weak interactions and molecular recognition in systems involving electron transfer proteins. CHEM REC 2002; 1:290-9. [PMID: 11893069 DOI: 10.1002/tcr.1014] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022]
Abstract
Electrostatic interactions and other weak interactions between amino acid side chains on protein surfaces play important roles in molecular recognition, and the mechanism of their intermolecular interactions has gained much interest. We established that charged peptides are useful for investigating the molecular recognition character of proteins and their molecular interaction induced structural changes. Positively charged lysine peptides competitively inhibited electron transfer from reduced cytochrome f (cyt f or cytochrome c (cyt c) to oxidized plastocyanin (PC), due to neutralization of the negatively charged site of PC by formation of PC-lysine peptide complexes. Lysine peptides also inhibited electron transfer from cyt c to cytochrome c peroxidase. Likewise, negatively charged aspartic acid peptides interacted with the positively charged sites of cytfand cyt c, and competitively inhibited electron transfer from reduced cytfor cyt c to oxidized PC and from [Fe(CN)6]4- to oxidized cyt c. Changes in the geometry and a shift to a higher redox potential of the active site Cu of PC on oligolysine binding were detected by spectroscopic and electrochemical measurements, owing to the absence of absorption in the visible region for lysine peptides. Structural and redox potential changes were also observed for cyt f and cyt c by interaction with aspartic acid peptides.
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Affiliation(s)
- S Hirota
- Department of Chemistry, Graduate School of Science, Nagoya University, Japan.
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26
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De Rienzo F, Gabdoulline RR, Menziani MC, De Benedetti PG, Wade RC. Electrostatic analysis and Brownian dynamics simulation of the association of plastocyanin and cytochrome f. Biophys J 2001; 81:3090-104. [PMID: 11720977 PMCID: PMC1301771 DOI: 10.1016/s0006-3495(01)75947-4] [Citation(s) in RCA: 73] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023] Open
Abstract
The oxidation of cytochrome f by the soluble cupredoxin plastocyanin is a central reaction in the photosynthetic electron transfer chain of all oxygenic organisms. Here, two different computational approaches are used to gain new insights into the role of molecular recognition and protein-protein association processes in this redox reaction. First, a comparative analysis of the computed molecular electrostatic potentials of seven single and multiple point mutants of spinach plastocyanin (D42N, E43K, E43N, E43Q/D44N, E59K/E60Q, E59K/E60Q/E43N, Q88E) and the wt protein was carried out. The experimentally determined relative rates (k(2)) for the set of plastocyanin mutants are found to correlate well (r(2) = 0.90 - 0.97) with the computed measure of the similarity of the plastocyanin electrostatic potentials. Second, the effects on the plastocyanin/cytochrome f association rate of these mutations in the plastocyanin "eastern site" were evaluated by simulating the association of the wild type and mutant plastocyanins with cytochrome f by Brownian dynamics. Good agreement between the computed and experimental relative rates (k(2)) (r(2) = 0.89 - 0.92) was achieved for the plastocyanin mutants. The results obtained by applying both computational techniques provide support for the fundamental role of the acidic residues at the plastocyanin eastern site in the association with cytochrome f and in the overall electron-transfer process.
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Affiliation(s)
- F De Rienzo
- Università di Modena e Reggio Emilia, Dipartimento di Chimica, Via Campi, 183-41100 Modena, Italy
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28
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Bergkvist A, Ejdebäck M, Ubbink M, Karlsson BG. Surface interactions in the complex between cytochrome f and the E43Q/D44N and E59K/E60Q plastocyanin double mutants as determined by (1)H-NMR chemical shift analysis. Protein Sci 2001; 10:2623-6. [PMID: 11714931 PMCID: PMC2374039 DOI: 10.1110/ps.27101] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/03/2001] [Revised: 08/29/2001] [Accepted: 08/31/2001] [Indexed: 10/21/2022]
Abstract
A combination of site-directed mutagenesis and NMR chemical shift perturbation analysis of backbone and side-chain protons has been used to characterize the transient complex of the photosynthetic redox proteins plastocyanin and cytochrome f. To elucidate the importance of charged residues on complex formation, the complex of cytochrome f and E43Q/D44N or E59K/E60Q spinach plastocyanin double mutants was studied by full analysis of the (1)H chemical shifts by use of two-dimensional homonuclear NMR spectra. Both mutants show a significant overall decrease in chemical shift perturbations compared with wild-type plastocyanin, in agreement with a large decrease in binding affinity. Qualitatively, the E43Q/D44N mutant showed a similar interaction surface as wild-type plastocyanin. The interaction surface in the E59K/E60Q mutant was distinctly different from wild type. It is concluded that all four charged residues contribute to the affinity and that residues E59 and E60 have an additional role in fine tuning the orientation of the proteins in the complex.
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Affiliation(s)
- A Bergkvist
- Biochemistry and Biophysics, Department of Chemistry, Göteborg University, SE-405 30 Göteborg, Sweden
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29
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Yamauchi O, Odani A, Hirota S. Metal Ion-Assisted Weak Interactions Involving Biological Molecules. From Small Complexes to Metalloproteins. BULLETIN OF THE CHEMICAL SOCIETY OF JAPAN 2001. [DOI: 10.1246/bcsj.74.1525] [Citation(s) in RCA: 60] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
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30
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van Amsterdam IM, Ubbink M, Jeuken LJ, Verbeet MP, Einsle O, Messerschmidt A, Canters GW. Effects of dimerization on protein electron transfer. Chemistry 2001; 7:2398-406. [PMID: 11446642 DOI: 10.1002/1521-3765(20010601)7:11<2398::aid-chem23980>3.0.co;2-l] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
Abstract
In order to investigate the relationship between the rate of protein-protein electron transfer and the structure of the association complex, a dimer of the blue copper protein azurin was constructed and its electron exchange properties were determined. For this purpose, a site for covalent cross-linking was engineered by replacing the surface-exposed asparagine 42 with a cysteine. This mutation enabled the formation of disulfide-linked homo-dimers of azurin. Based on NMR line-broadening experiments, the electron self-exchange (e.s.e.) rate constant for this dimer was determined to be 4.2(+/-0.7) x 10(5)M(-1)s(-1), which is a seven-fold decrease relative to wild-type azurin. This difference is ascribed to a less accessible hydrophobic patch in the dimer. To discriminate between intramolecular electron transfer within a dimer and intermolecular electron transfer between two dimers, the e.s.e. rate constant of (Cu-Cu)-N42C dimers was compared with that of (Zn-Cu)- and (Ag-Cu)-N42C dimers. As Zn and Ag are redox inactive, the intramolecular electron transfer reaction in these latter dimers can be eliminated. The e.s.e. rate constants of the three dimers are the same and an upper limit for the intramolecular electron transfer rate of 10 s(-1) could be determined. This rate is compatible with a Cu-Cu distance of 18 A or more, which is larger than the Cu - Cu distance of 15 A observed in the wild-type crystal structure that shows two monomers that face each other with opposing hydrophobic patches. Modelling of the dimer shows that the Cu-Cu distance should be in the range of 17 A < rCu-Cu < 28 A, which is in agreement with the experimental findings. For efficient electron transfer, it appears crucial that the two molecules interact in the proper orientation. Direct cross-linking may disturb the formation of such an optimal electron transfer complex.
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31
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Formosinho SJ, Arnaut LG. Theory of electron transfer reactions in blue-copper proteins. RESEARCH ON CHEMICAL INTERMEDIATES 2001. [DOI: 10.1163/156856701745168] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
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32
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De Rienzo F, Gabdoulline RR, Menziani MC, Wade RC. Blue copper proteins: a comparative analysis of their molecular interaction properties. Protein Sci 2000; 9:1439-54. [PMID: 10975566 PMCID: PMC2144732 DOI: 10.1110/ps.9.8.1439] [Citation(s) in RCA: 91] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
Abstract
Blue copper proteins are type-I copper-containing redox proteins whose role is to shuttle electrons from an electron donor to an electron acceptor in bacteria and plants. A large amount of experimental data is available on blue copper proteins; however, their functional characterization is hindered by the complexity of redox processes in biological systems. We describe here the application of a semiquantitative method based on a comparative analysis of molecular interaction fields to gain insights into the recognition properties of blue copper proteins. Molecular electrostatic and hydrophobic potentials were computed and compared for a set of 33 experimentally-determined structures of proteins from seven blue copper subfamilies, and the results were quantified by means of similarity indices. The analysis provides a classification of the blue copper proteins and shows that (I) comparison of the molecular electrostatic potentials provides useful information complementary to that highlighted by sequence analysis; (2) similarities in recognition properties can be detected for proteins belonging to different subfamilies, such as amicyanins and pseudoazurins, that may be isofunctional proteins; (3) dissimilarities in interaction properties, consistent with experimentally different binding specificities, may be observed between proteins belonging to the same subfamily, such as cyanobacterial and eukaryotic plastocyanins; (4) proteins with low sequence identity, such as azurins and pseudoazurins, can have sufficient similarity to bind to similar electron donors and acceptors while having different binding specificity profiles.
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Affiliation(s)
- F De Rienzo
- European Molecular Biology Laboratory, Heidelberg, Germany
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33
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Gong XS, Wen JQ, Fisher NE, Young S, Howe CJ, Bendall DS, Gray JC. The role of individual lysine residues in the basic patch on turnip cytochrome f for electrostatic interactions with plastocyanin in vitro. EUROPEAN JOURNAL OF BIOCHEMISTRY 2000; 267:3461-8. [PMID: 10848961 DOI: 10.1046/j.1432-1327.2000.01366.x] [Citation(s) in RCA: 36] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
The role of electrostatic interactions in determining the rate of electron transfer between cytochrome f and plastocyanin has been examined in vitro with mutants of turnip cytochrome f and mutants of pea and spinach plastocyanins. Mutation of lysine residues Lys58, Lys65 and Lys187 of cytochrome f to neutral or acidic residues resulted in decreased binding constants and decreased rates of electron transfer to wild-type pea plastocyanin. Interaction of the cytochrome f mutant K187E with the pea plastocyanin mutant D51K gave a further decrease in electron transfer rate, indicating that a complementary charge pair at these positions could not compensate for the decreased overall charge on the proteins. Similar results were obtained with the interaction of the cytochrome f mutant K187E with single, double and triple mutants of residues in the acidic patches of spinach plastocyanin. These results suggest that the lysine residues of the basic patch on cytochrome f are predominantly involved in long-range electrostatic interactions with plastocyanin. However, analysis of the data using thermodynamic cycles provided evidence for the interaction of Lys187 of cytochrome f with Asp51, Asp42 and Glu43 of plastocyanin in the complex, in agreement with a structural model of a cytochrome f-plastocyanin complex determined by NMR.
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Affiliation(s)
- X S Gong
- Cambridge Centre for Molecular Recognition and Department of Plant Sciences, University of Cambridge, UK
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34
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Gong XS, Wen JQ, Gray JC. The role of amino-acid residues in the hydrophobic patch surrounding the haem group of cytochrome f in the interaction with plastocyanin. EUROPEAN JOURNAL OF BIOCHEMISTRY 2000; 267:1732-42. [PMID: 10712605 DOI: 10.1046/j.1432-1327.2000.01168.x] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Soluble turnip cytochrome f has been purified from the periplasmic fraction of Escherichia coli expressing a truncated petA gene encoding the precursor protein lacking the C-terminal 33 amino-acid residues. The protein is identical [as judged by 1H-NMR spectroscopy, midpoint redox potential (+ 365 mV) and electron transfer reactions with plastocyanin] to cytochrome f purified from turnip leaves. Several residues in the hydrophobic patch surrounding the haem group have been changed by site-directed mutagenesis, and the proteins purified from E. coli. The Y1F and Q7N mutants showed only minor changes in the plastocyanin-binding constant Ka and the second-order rate constant for electron transfer to plastocyanin, whereas the Y160S mutant showed a 30% decrease in the overall rate of electron transfer caused in part by a 60% decrease in binding constant and partially compensated by an increased driving force due to a 27-mV decrease in redox potential. In contrast, the F4Y mutant showed increased rates of electron transfer which may be ascribed to an increased binding constant and a 14-mV decrease in midpoint redox potential. This indicates that subtle changes in the hydrophobic patch can influence rates of electron transfer to plastocyanin by changing the binding constants and altering the midpoint redox potential of the cytochrome haem group.
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Affiliation(s)
- X S Gong
- Department of Plant Sciences and Cambridge Centre for Molecular Recognition, University of Cambridge, UK
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35
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Taneva SG, Donchev AA, Dimitrov MI, Muga A. Redox- and pH-dependent association of plastocyanin with lipid bilayers: effect on protein conformation and thermal stability. BIOCHIMICA ET BIOPHYSICA ACTA 2000; 1463:429-38. [PMID: 10675519 DOI: 10.1016/s0005-2736(99)00230-8] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
Abstract
The effect of electrostatic interactions on the conformation and thermal stability of plastocyanin (Pc) was studied by infrared spectroscopy. Association of any of the two redox states of the protein with positively charged membranes at neutral pH does not significantly change the secondary structure of Pc. However, upon membrane binding, the denaturation temperature decreases, regardless of the protein redox state. The extent of destabilization depends on the proportion of positively charged lipid headgroups in the membrane, becoming greater as the surface density of basic phospholipids increases. In contrast, at pH 4.8 the membrane binding-dependent conformational change becomes redox-sensitive. While the secondary structures and thermal stabilities of free and membrane-bound oxidized Pc are similar under acidic conditions, the conformation of the reduced form of the protein drastically rearranges upon membrane association. This rearrangement does not depend on electrostatic interactions to occur, since it is also observed in the presence of uncharged lipid bilayers. The conformational transition, only observed for reduced Pc, involves the exposure of hydrophobic regions that leads to intermolecular interactions at the membrane surface. Membrane-mediated partial unfolding of reduced Pc can be reversed by readjusting the pH to neutrality, in the absence of electrostatic interactions. This redox-dependent behavior might reflect specific structural requirements for the interaction of Pc with its redox partners.
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Affiliation(s)
- S G Taneva
- Unidad de Biofísica (CSIC - UPV/EHU), and Departamento de Bioquímica y Biología Molecular, Universidad del País Vasco, Aptdo. 644, 48080, Bilbao, Spain
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36
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Ullmann GM, Hauswald M, Jensen A, Knapp EW. Structural alignment of ferredoxin and flavodoxin based on electrostatic potentials: Implications for their interactions with photosystem I and ferredoxin-NADP reductase. Proteins 2000. [DOI: 10.1002/(sici)1097-0134(20000215)38:3<301::aid-prot6>3.0.co;2-y] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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37
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Kohzuma T, Inoue T, Yoshizaki F, Sasakawa Y, Onodera K, Nagatomo S, Kitagawa T, Uzawa S, Isobe Y, Sugimura Y, Gotowda M, Kai Y. The structure and unusual pH dependence of plastocyanin from the fern Dryopteris crassirhizoma. The protonation of an active site histidine is hindered by pi-pi interactions. J Biol Chem 1999; 274:11817-23. [PMID: 10206999 DOI: 10.1074/jbc.274.17.11817] [Citation(s) in RCA: 71] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Spectroscopic properties, amino acid sequence, electron transfer kinetics, and crystal structures of the oxidized (at 1.7 A resolution) and reduced form (at 1.8 A resolution) of a novel plastocyanin from the fern Dryopteris crassirhizoma are presented. Kinetic studies show that the reduced form of Dryopteris plastocyanin remains redox-active at low pH, under conditions where the oxidation of the reduced form of other plastocyanins is inhibited by the protonation of a solvent-exposed active site residue, His87 (equivalent to His90 in Dryopteris plastocyanin). The x-ray crystal structure analysis of Dryopteris plastocyanin reveals pi-pi stacking between Phe12 and His90, suggesting that the active site is uniquely protected against inactivation. Like higher plant plastocyanins, Dryopteris plastocyanin has an acidic patch, but this patch is located closer to the solvent-exposed active site His residue, and the total number of acidic residues is smaller. In the reactions of Dryopteris plastocyanin with inorganic redox reagents, the acidic patch (the "remote" site) and the hydrophobic patch surrounding His90 (the "adjacent" site) are equally efficient for electron transfer. These results indicate the significance of the lack of protonation at the active site of Dryopteris plastocyanin, the equivalence of the two electron transfer sites in this protein, and a possibility of obtaining a novel insight into the photosynthetic electron transfer system of the first vascular plant fern, including its molecular evolutionary aspects. This is the first report on the characterization of plastocyanin and the first three-dimensional protein structure from fern plant.
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Affiliation(s)
- T Kohzuma
- Faculty of Science, Ibaraki University, Mito, Ibaraki 310-8512, Japan.
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38
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Spectroscopic characterization and kinetic studies of a novel plastocyanin from the green alga Ulva pertusa. Inorganica Chim Acta 1998. [DOI: 10.1016/s0020-1693(98)00228-x] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
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39
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Pearson DC, Gross EL. Brownian dynamics study of the interaction between plastocyanin and cytochrome f. Biophys J 1998; 75:2698-711. [PMID: 9826593 PMCID: PMC1299944 DOI: 10.1016/s0006-3495(98)77714-8] [Citation(s) in RCA: 62] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022] Open
Abstract
The electrostatic interaction between plastocyanin (PC) and cytochrome f (cyt f), electron transfer partners in photosynthesis was studied using Brownian dynamics (BD) simulations. By using the software package MacroDox, which implements the BD algorithm of Northrup et al. (Northrup, S. H., J. O. Boles, and J. C. L. Reynolds. 1987. J. Phys. Chem. 91:5991-5998), we have modeled the interaction of the two proteins based on crystal structures of poplar PC and turnip cyt f at pH 7 and a variety of ionic strengths. We find that the electrostatic attraction between positively charged residues (K58, K65, K187, and R209, among others) on cyt f and negatively charged residues (E43, D44, E59, and E60, among others) on PC steers PC into a single dominant orientation with respect to cyt f, and furthermore, that the single dominant orientation that we observe is one that we had predicted in our previous work (Pearson, D. C., E. L. Gross, and E. S. David. 1996. Biophys. J. 71:64-76). This dominant orientation permits the formation of hydrophobic interactions, which are not implemented in the MacroDox algorithm. This proposed complex between PC and cyt f implicates H87, a copper ligand on PC, as the residue that accepts electrons from the heme on cyt f (and possibly through Y1 as we proposed previously). We argue for the existence of this single dominant complex on the basis of observations that the most favorable orientations of the interaction between PC and cyt f, as determined by grouping successful BD trajectories on the basis of closest contacts of charged residues, tend to overlap one another and have very close distances between the metal centers on the two proteins (copper on PC, iron on cyt f). We use this knowledge to develop a model for PC/cyt f interaction that places a reaction between the two proteins occurring when the copper-to-iron distance is between 16 and 17 A. This reaction distance gives a good estimate of the experimentally observed rate constant for PC-cyt f interaction. Analysis of BD results as a function of ionic strength predicts an interaction that happens less frequently and becomes less specific as ionic strength increases.
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Affiliation(s)
- D C Pearson
- Department of Biochemistry and Biophysics Program, The Ohio State University, Columbus, Ohio 43210 USA
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Salamon Z, Huang D, Cramer WA, Tollin G. Coupled plasmon-waveguide resonance spectroscopy studies of the cytochrome b6f/plastocyanin system in supported lipid bilayer membranes. Biophys J 1998; 75:1874-85. [PMID: 9746528 PMCID: PMC1299858 DOI: 10.1016/s0006-3495(98)77628-3] [Citation(s) in RCA: 43] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/08/2023] Open
Abstract
The incorporation of cytochrome (cyt) b6f into a solid-supported planar egg phosphatidylcholine (PC) bilayer membrane and complex formation with plastocyanin have been studied by a variant of surface plasmon resonance called coupled plasmon-waveguide resonance (CPWR) spectroscopy, developed in our laboratory. CPWR combines greatly enhanced sensitivity and spectral resolution with direct measurement of anisotropies in refractive index and optical extinction coefficient, and can therefore probe structural properties of lipid-protein and protein-protein interactions. Cyt b6f incorporation into the membrane proceeds in two stages. The first occurs at low protein concentration and is characterized by an increase in total proteolipid mass without significant changes in the molecular order of the system, as demonstrated by shifts of the resonance position to larger incident angles without changing the refractive index anisotropy. The second stage, occurring at higher protein concentrations, results in a decrease in both the mass density and the molecular order of the system, evidenced by shifts of the resonance position to smaller incident angles and a large decrease in the membrane refractive index anisotropy. Plastocyanin can bind to such a proteolipid system in three different ways. First, the addition of plastocyanin before the second stage of b6f incorporation begins results in complex formation between the two proteins with a KD of approximately 10 microM and induces structural changes in the membrane that are similar to those occurring during the second stage of complex incorporation. The addition of larger amounts of plastocyanin under these conditions leads to nonspecific binding to the lipid phase with a KD of approximately 180 microM. Finally, the addition of plastocyanin after the completion of the second phase of b6f incorporation results in tighter binding between the two proteins (KD approximately 1 microM). Quantitation of the binding stoichiometry indicates that two plastocyanin molecules bind tightly to the dimeric form of the cyt b6f complex, assuming random insertion of the cytochrome into the bilayer. The structural basis for these results and formation of the proteolipid membrane are discussed.
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Affiliation(s)
- Z Salamon
- Department of Biochemistry, University of Arizona, Tucson, Arizona 85721, USA
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Ubbink M, Ejdebäck M, Karlsson BG, Bendall DS. The structure of the complex of plastocyanin and cytochrome f, determined by paramagnetic NMR and restrained rigid-body molecular dynamics. Structure 1998; 6:323-35. [PMID: 9551554 DOI: 10.1016/s0969-2126(98)00035-5] [Citation(s) in RCA: 246] [Impact Index Per Article: 9.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
BACKGROUND The reduction of plastocyanin by cytochrome f is part of the chain of photosynthetic electron transfer reactions that links photosystems II and I. The reaction is rapid and is influenced by charged residues on both proteins. Previously determined structures show that the plastocyanin copper and cytochrome f haem redox centres are some distance apart from the relevant charged sidechains, and until now it was unclear how a transient electrostatic complex can be formed that brings the redox centres sufficiently close for a rapid reaction. RESULTS A new approach was used to determine the structure of the transient complex between cytochrome f and plastocyanin. Diamagnetic chemical shift changes and intermolecular pseudocontact shifts in the NMR spectrum of plastocyanin were used as input in restrained rigid-body molecular dynamics calculations. An ensemble of ten structures was obtained, in which the root mean square deviation of the plastocyanin position relative to cytochrome f is 1.0 A. Electrostatic interaction is maintained at the same time as the hydrophobic side of plastocyanin makes close contact with the haem area, thus providing a short electron transfer pathway (Fe-Cu distance 10.9 A) via residues Tyr1 or Phe4 (cytochrome f) and the copper ligand His87 (plastocyanin). CONCLUSIONS The combined use of diamagnetic and paramagnetic chemical shift changes makes it possible to obtain detailed information about the structure of a transient complex of redox proteins. The structure suggests that the electrostatic interactions 'guide' the partners into a position that is optimal for electron transfer, and which may be stabilised by short-range interactions.
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Affiliation(s)
- M Ubbink
- Department of Biochemistry, University of Cambridge, England.
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Soriano GM, Cramer WA, Krishtalik LI. Electrostatic effects on electron-transfer kinetics in the cytochrome f-plastocyanin complex. Biophys J 1997; 73:3265-76. [PMID: 9414237 PMCID: PMC1181228 DOI: 10.1016/s0006-3495(97)78351-6] [Citation(s) in RCA: 36] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023] Open
Abstract
In a complex of two electron-transfer proteins, their redox potentials can be shifted due to changes in the dielectric surroundings and the electrostatic potentials at each center caused by the charged residues of the partner. These effects are dependent on the geometry of the complex. Three different docking configurations (DCs) for intracomplex electron transfer between cytochrome f and plastocyanin were studied, defined by 1) close contact of the positively charged region of cytochrome f and the negatively charged regions of plastocyanin (DC1) and by (2, 3) close contact of the surface regions adjacent to the Fe and Cu redox centers (DC2 and DC3). The equilibrium energetics for electron transfer in DC1-DC3 are the same within approximately +/-0.1 kT. The lower reorganization energy for DC2 results in a slightly lower activation energy for this complex compared with DC1 and DC3. The long heme-copper distance (approximately 24 A) in the DC1 complex drastically decreases electronic coupling and makes this complex much less favorable for electron transfer than DC2 or DC3. DC1-like complexes can only serve as docking intermediates in the pathway toward formation of an electron-transfer-competent complex. Elimination of the four positive charges arising from the lysine residues in the positive patch of cytochrome f, as accomplished by mutagenesis, exerts a negligible effect (approximately 3 mV) on the redox potential difference between cyt f and PC.
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Affiliation(s)
- G M Soriano
- Department of Biological Sciences, Purdue University, West Lafayette, IN 47907-1392, USA
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43
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Ubbink M, Lian LY, Modi S, Evans PA, Bendall DS. Analysis of the 1H-NMR chemical shifts of Cu(I)-, Cu(II)- and Cd-substituted pea plastocyanin. Metal-dependent differences in the hydrogen-bond network around the copper site. EUROPEAN JOURNAL OF BIOCHEMISTRY 1996; 242:132-47. [PMID: 8954163 DOI: 10.1111/j.1432-1033.1996.0132r.x] [Citation(s) in RCA: 42] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/03/2023]
Abstract
To compare cadmium-substituted plastocyanin with copper plastocyanin, the 1H-NMR spectra of CuI-, CuII- and Cd-plastocyanin from pea have been analyzed. Full assignments of the spectra of CuI- and Cd-plastocyanin indicate chemical shift differences up to 1 ppm. The affected protons are located in the four loops that surround the Cu site. The largest differences were found for protons in the hydrogen bond network which stabilizes this part of the protein. This suggests that the chemical shift differences are caused by very small but extensive structural changes in the network upon replacement of CuI by Cd. For CuII-plastocyanin the resonances of 72% of the protons observed in the CuI form have been identified. Protons within approximately 0.9 nm of the CuII were not observed due to fast paramagnetic relaxation. The protons between 0.9-1.7 nm from the CuII showed chemical shift differences up to 0.4 ppm compared to both CuI- and Cd-plastocyanin. These differences can be predicted assuming that they represent pseudocontact shifts. When corrected for the pseudocontact shift contribution, the CuII-plastocyanin chemical shifts were nearly all identical within error to those of the Cd form, but not of the CuI-plastocyanin, indicating that the CuII-plastocyanin structure, in as far as it can be observed, resembles Cd-rather than CuI-plastocyanin. In a single stretch of residues (64-69) chemical shift differences remained between all three forms after correction. The fact that pseudocontact shifts were observed for protons which were not broadened may be attributable to the weaker distance dependence of the pseudocontact shift effect compared to paramagnetic relaxation. This results in two shells around the Cu atom, an inner paramagnetic shell (0-0.9 nm), in which protons are not observed due to broadening, and an outer paramagnetic shell (0.9-1.7 nm), in which protons can be observed and show pseudocontact shifts. It is concluded that Cd-plastocyanin is a suitable redox-inactive substitute for Cu-plastocyanin.
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Affiliation(s)
- M Ubbink
- Department of Biochemistry, University of Cambridge, England.
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44
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Kannt A, Young S, Bendall DS. The role of acidic residues of plastocyanin in its interaction with cytochrome ƒ. BIOCHIMICA ET BIOPHYSICA ACTA-BIOENERGETICS 1996. [DOI: 10.1016/s0005-2728(96)00090-4] [Citation(s) in RCA: 96] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
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45
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Wagner MJ, Packer JC, Howe CJ, Bendall DS. Some characteristics of cytochrome f in the cyanobacterium Phormidium laminosum: its sequence and charge properties in the reaction with plastocyanin. BIOCHIMICA ET BIOPHYSICA ACTA 1996; 1276:246-52. [PMID: 8856106 DOI: 10.1016/0005-2728(96)00084-9] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Abstract
Part of the petCA operon was cloned and the sequence of the cytochrome f gene from the moderately thermophilic cyanobacterium Phormidium laminosum determined. A partial sequence of the petC gene encoding the Rieske iron-sulphur protein was also obtained. The cytochrome f gene encodes a mature protein of 385 residues and a leader sequence of 45 residues. The mature protein contains several acidic or neutral residues corresponding to basic residues in the turnip protein. Some of the latter are thought to be important for the interaction with plastocyanin via its "eastern' face. Many of the corresponding residues on the eastern face of P. laminosum plastocyanin are either basic or neutral instead of acidic. These comparisons suggested that the local charges on P. laminosum cytochrome f that are important for its interaction with the homologous plastocyanin may be negative rather than positive. The importance of acidic groups was confirmed by measuring the rates of reduction of horse heart cytochrome c and P. laminosum and spinach plastocyanins by the cytochrome bf complex isolated from P. laminosum. P. laminosum plastocyanin gave the highest rates, which decreased at high ionic strength, confirming the importance of positive local charges on this protein. When extrapolated to infinite ionic strength the rates observed with the two kinds of plastocyanin were similar, but cytochrome c became unreactive. An optimum was observed in the ionic strength response with P. laminosum plastocyanin.
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Affiliation(s)
- M J Wagner
- Department of Biochemistry, University of Cambridge, UK
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46
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Pearson DC, Gross EL, David ES. Electrostatic properties of cytochrome f: implications for docking with plastocyanin. Biophys J 1996; 71:64-76. [PMID: 8804589 PMCID: PMC1233457 DOI: 10.1016/s0006-3495(96)79236-6] [Citation(s) in RCA: 48] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023] Open
Abstract
The electrostatic properties of cytochrome f (cyt f), a member of the cytochrome b6f complex and reaction partner with plastocyanin (PC) in photosynthetic electron transport, are qualitatively studied with the goal of determining the mechanism of electron transfer between cyt f and PC. A crystal structure for cyt f was analyzed with the software package GRASP, revealing a large region of positive potential generated by a patch of positively charged residues (including K58, K65, K66, K122, K185, K187, and R209) and reinforced by the iron center of the heme. This positive field attracts the negative charges of the two acidic patches on the mobile electron carrier PC. Three docked complexes are obtained for the two proteins, based on electrostatic or hydrophobic interactions or both and on steric fits by manual docking methods. The first of these three complexes shows strong electrostatic interactions between K187 on cyt f and D44 on PC and between E59 on PC and K58 on cyt f. Two other manually docked complexes are proposed, implicating H87 on PC as the electron-accepting site from the iron center of cyt f through Y1. The second complex maintains the D44/K187 cross-link (but not the E59/K58 link) while increasing hydrophobic interactions between PC and cyt f. Hydrophobic interactions are increased still further in the third complex, whereas the link between K187 on cyt f and D44 on PC is broken. The proposed reaction mechanism, therefore, involves an initial electrostatic docking complex that gives rise to a nonpolar attraction between the regions surrounding H87 on PC and Y1 on cyt f, providing for an electron-transfer active complex.
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Affiliation(s)
- D C Pearson
- Department of Biochemistry, Ohio State University, Columbus 43210, USA
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47
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Cramer WA, Soriano GM, Ponomarev M, Huang D, Zhang H, Martinez SE, Smith JL. SOME NEW STRUCTURAL ASPECTS AND OLD CONTROVERSIES CONCERNING THE CYTOCHROME b6f COMPLEX OF OXYGENIC PHOTOSYNTHESIS. ACTA ACUST UNITED AC 1996; 47:477-508. [PMID: 15012298 DOI: 10.1146/annurev.arplant.47.1.477] [Citation(s) in RCA: 164] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
The cytochrome b6f complex functions in oxygenic photosynthetic membranes as the redox link between the photosynthetic reaction center complexes II and I and also functions in proton translocation. It is an ideal integral membrane protein complex in which to study structure and function because of the existence of a large amount of primary sequence data, purified complex, the emergence of structures, and the ability of flash kinetic spectroscopy to assay function in a readily accessible ms-100 mus time domain. The redox active polypeptides are cytochromes f and b6 (organelle encoded) and the Rieske iron-sulfur protein (nuclear encoded) in a mol wt = 210,000 dimeric complex that is believed to contain 22-24 transmembrane helices. The high resolution structure of the lumen-side domain of cytochrome f shows it to be an elongate (75 A long) mostly beta-strand, two-domain protein, with the N-terminal alpha-amino group as orthogonal heme ligand and an internal linear 11-A bound water chain. An unusual electron transfer event, the oxidant-induced reduction of a significant fraction of the p (lumen)-side cytochrome b heme by plastosemiquinone indicates that the electron transfer pathway in the b6f complex can be described by a version of the Q-cycle mechanism, originally proposed to describe similar processes in the mitochondrial and bacterial bc1 complexes.
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Affiliation(s)
- W. A. Cramer
- Department of Biological Sciences, Purdue University, West Lafayette, Indiana 49707-1392
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48
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Qin L, Kostić NM. Enforced interaction of one molecule of plastocyanin with two molecules of cytochrome c and an electron-transfer reaction involving the hydrophobic patch on the plastocyanin surface. Biochemistry 1996; 35:3379-86. [PMID: 8639487 DOI: 10.1021/bi9516586] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023]
Abstract
Laser flash photolysis is used to study the photoinduced electron-transfer reaction cyt(III)//pc(II) + 3Zncyt --> cyt(III)//pc(I) + Zincyt+ at pH 7.0 and 25 degrees. In the covalent (symbol//) complex cyt(III)//pc(II) the acidic patch in cupriplastocyanin is directly cross-linked to the basic patch in ferricytochrome c. The triplet state of zinc cytochrome c reduces the pc(II) moiety, not the cyt(III) moiety, of the covalent complex. The reaction is strictly bimolecular in the entire range of ionic strength studied, from 1.25 mM to 1.00 M. The two reactants interact only transiently, in a collisional complex, and do not form a persistent complex cyt(III)//pc(II)/Zncyt. Because noncovalent (symbol/) association of three separate protein molecules is far less probable than association of the covalent complex and another protein molecule, we conclude that, without the aid of covalent cross-links, one molecule of plastocyanin will not form a ternary complex with two molecules of cytochrome c, cyt/pc/cyt. Dependence of the rate constant on ionic strength is analyzed in terms of van Leeuwen theory of electrostatic interactions, which recognizes the importance of dipole moments of the proteins. This analysis shows that 3Zncyt reacts with the hydrophobic patch in the pc(II) moiety of the covalent complex cyt(III)//pc(II). At high ionic strength, at which electrostatic interactions are practically abolished, the blue copper site is reduced with approximately equal rates via the hydrophobic patch in the pc(II) moiety of the complex and via the acidic patch in free pc(II). This is evidence that the two distinct patches on the plastocyanin surface are comparable in their intrinsic "conductivity" for electrons coming to the copper site. Positively charged and electroneutral redox partners tend to react at the acidic patch (although not necessarily at the initial docking site in this broad patch) for electrostatic, not electronic, reasons. Earlier theorectical studies disagreed about the relative electronic conductivities of the two patches. This experimental study corroborates very recent theoretical studies that found the two patches to be comparable in the efficiency of electron transfer.
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Affiliation(s)
- L Qin
- Department of Chemistry, Iowa State University, Ames 50011, USA
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49
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A method to analyze multi-pathway effects on protein mediated donor-acceptor coupling interactions. Inorganica Chim Acta 1996. [DOI: 10.1016/0020-1693(96)04904-3] [Citation(s) in RCA: 22] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
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50
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de Rege PJ, Williams SA, Therien MJ. Direct evaluation of electronic coupling mediated by hydrogen bonds: implications for biological electron transfer. Science 1995; 269:1409-13. [PMID: 7660123 DOI: 10.1126/science.7660123] [Citation(s) in RCA: 203] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
Abstract
Three supramolecular bischromophoric systems featuring zinc(II) and iron(III) porphyrins have been synthesized to evaluate the relative magnitudes of electronic coupling provided by hydrogen, sigma, and pi bonds. Laser flash excitation generates the highly reducing singlet excited state of the (porphinato)zinc chromophore that can subsequently be electron transfer quenched by the (porphinato)iron(III) chloride moiety. Measurement of the photoinduced electron transfer rate constants enables a direct comparison of how well these three types of chemical interactions facilitate electron tunneling. In contrast to generally accepted theory, electronic coupling modulated by a hydrogen-bond interface is greater than that provided by an analogous interface composed entirely of carbon-carbon sigma bonds. These results bear considerably on the analysis of through-protein electron transfer rate data as well as on the power of theory to predict the path traversed by the tunneling electron in a biological matrix; moreover, they underscore the cardinal role played by hydrogen bonds in biological electron transfer processes.
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Affiliation(s)
- P J de Rege
- Department of Chemistry, University of Pennsylvania, Philadelphia 19104-6323, USA
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