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Bhaduri S, Zhang H, Erramilli S, Cramer WA. Structural and functional contributions of lipids to the stability and activity of the photosynthetic cytochrome b 6 f lipoprotein complex. J Biol Chem 2019; 294:17758-17767. [PMID: 31597701 DOI: 10.1074/jbc.ra119.009331] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/12/2019] [Revised: 10/08/2019] [Indexed: 11/06/2022] Open
Abstract
The photosynthetic cytochrome b 6 f complex, a homodimer containing eight distinct subunits and 26 transmembrane helices per monomer, catalyzes proton-coupled electron transfer across the thylakoid membrane. The 2.5-Å-resolution structure of the complex from the cyanobacterium Nostoc sp. revealed the presence of 23 lipid-binding sites per monomer. Although the crystal structure of the cytochrome b 6 f from a plant source has not yet been solved, the identities of the lipids present in a plant b 6 f complex have previously been determined, indicating that the predominant lipid species are monogalactosyldiacylglycerol (MGDG), digalactosyldiacylglycerol (DGDG), phosphatidylglycerol (PG), and sulfoquinovosyldiacylglycerol (SQDG). Despite the extensive structural analyses of b 6 f-lipid interactions, the basis of the stabilization by lipids remains poorly understood. In the present study, we report on the effect of individual lipids on the structural and functional integrity of the b 6 f complex, purified from Spinacea oleracea It was found that (i) galactolipids (MGDG, DGDG, and SQDG) and phospholipids dilinolenoyl-phosphatidylglycerol (DLPG), 1,2-dioleoylphosphatidylglycerol (DOPG), and 1,2-dioleoyl-sn-glycerol-3-phosphatidylcholine (DOPC) structurally stabilize the complex to varying degrees; (ii) SQDG has a major role in stabilizing the dimeric complex; (iii) the b 6 f complex is stabilized by incorporation into nanodiscs or bicelles; (iv) removal of bound phospholipid by phospholipase A2 inactivates the cytochrome complex; and (v) activity can be restored significantly by the addition of the anionic lipid PG, which is attributed to stabilization of the quinone portal and the hinge region of the iron-sulfur protein.
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Affiliation(s)
- Satarupa Bhaduri
- Department of Biological Sciences, Purdue University, West Lafayette, Indiana 47906
| | - Huamin Zhang
- SSCI, a Division of Albany Molecular Research Inc., West Lafayette, Indiana 47906
| | - Satchal Erramilli
- Department of Biochemistry and Molecular Biophysics, University of Chicago, Chicago, Illinois 60637
| | - William A Cramer
- Department of Biological Sciences, Purdue University, West Lafayette, Indiana 47906
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Agarwal R, Chauvet AAP. Ultrafast dynamics of the photo-excited hemes b and c n in the cytochrome b 6f complex. Phys Chem Chem Phys 2017; 19:3287-3296. [PMID: 28085168 DOI: 10.1039/c6cp08077d] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
The dynamics of hemes b and cn within the cytochrome b6f complex are investigated by means of ultrafast broad-band transient absorption spectroscopy. On the one hand, the data reveal that, subsequent to visible light excitation, part of the b hemes undergoes pulse-limited photo-oxidation, with the liberated electron supposedly being transferred to one of the adjacent aromatic amino acids. Photo-oxidation is followed by charge recombination in about 8.2 ps. Subsequent to charge recombination, heme b is promoted to a vibrationally excited ground state that relaxes in about 4.6 ps. On the other hand, heme cn undergoes ultrafast ground state recovery in about 140 fs. Interestingly, the data also show that, in contrast to previous beliefs, Chl a is involved in the photochemistry of hemes. Indeed, subsequent to heme excitation, Chl a bleaches and recovers to its ground state in 90 fs and 650 fs, respectively. Chl a bleaching allegedly corresponds to the formation of a short lived Chl a anion. Beyond the previously suggested structural role, this study provides unique evidence that Chl a is directly involved in the photochemistry of the hemes.
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Affiliation(s)
- Rachna Agarwal
- Department of Biological Sciences, Purdue University, West Lafayette, Indiana 47907, USA and Molecular Biology Division, Bhabha Atomic Research Centre, Mumbai 400 085, India
| | - Adrien A P Chauvet
- Ecole Polytechnique Fédérale de Lausanne (EPFL), Laboratoire de Spectroscopie Ultrarapide (LSU), ISIC, Faculté des Sciences de Base and Lausanne Centre for Ultrafast Science (LACUS), Station 6, 1015 Lausanne, Switzerland. and The University of Sheffield, Department of Chemistry, Dainton Building, Brook Hill, Sheffield S3 7HF, UK
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Singh SK, Hasan SS, Zakharov SD, Naurin S, Cohn W, Ma J, Whitelegge JP, Cramer WA. Trans-membrane Signaling in Photosynthetic State Transitions: REDOX- AND STRUCTURE-DEPENDENT INTERACTION IN VITRO BETWEEN STT7 KINASE AND THE CYTOCHROME b6f COMPLEX. J Biol Chem 2016; 291:21740-21750. [PMID: 27539852 DOI: 10.1074/jbc.m116.732545] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/14/2016] [Revised: 08/01/2016] [Indexed: 12/11/2022] Open
Abstract
Trans-membrane signaling involving a serine/threonine kinase (Stt7 in Chlamydomonas reinhardtii) directs light energy distribution between the two photosystems of oxygenic photosynthesis. Oxidation of plastoquinol mediated by the cytochrome b6f complex on the electrochemically positive side of the thylakoid membrane activates the kinase domain of Stt7 on the trans (negative) side, leading to phosphorylation and redistribution ("state transition") of the light-harvesting chlorophyll proteins between the two photosystems. The molecular description of the Stt7 kinase and its interaction with the cytochrome b6f complex are unknown or unclear. In this study, Stt7 kinase has been cloned, expressed, and purified in a heterologous host. Stt7 kinase is shown to be active in vitro in the presence of reductant and purified as a tetramer, as determined by analytical ultracentrifugation, electron microscopy, and electrospray ionization mass spectrometry, with a molecular weight of 332 kDa, consisting of an 83.41-kDa monomer. Far-UV circular dichroism spectra show Stt7 to be mostly α-helical and document a physical interaction with the b6f complex through increased thermal stability of Stt7 secondary structure. The activity of wild-type Stt7 and its Cys-Ser mutant at positions 68 and 73 in the presence of a reductant suggest that the enzyme does not require a disulfide bridge for its activity as suggested elsewhere. Kinase activation in vivo could result from direct interaction between Stt7 and the b6f complex or long-range reduction of Stt7 by superoxide, known to be generated in the b6f complex by quinol oxidation.
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Affiliation(s)
| | | | | | | | - Whitaker Cohn
- the Pasarow Mass Spectrometry Laboratory, NPI-Semel Institute, David Geffen School of Medicine, University of California, Los Angeles, California 90024
| | - Jia Ma
- Biophysical Analysis Laboratory, Bindley Bioscience Center,Purdue University, West Lafayette, Indiana 47907 and
| | - Julian P Whitelegge
- the Pasarow Mass Spectrometry Laboratory, NPI-Semel Institute, David Geffen School of Medicine, University of California, Los Angeles, California 90024
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Structure-Function of the Cytochrome b 6 f Lipoprotein Complex. ADVANCES IN PHOTOSYNTHESIS AND RESPIRATION 2016. [DOI: 10.1007/978-94-017-7481-9_9] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/04/2023]
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Mechanisms of Superoxide Generation and Signaling in Cytochrome bc Complexes. ADVANCES IN PHOTOSYNTHESIS AND RESPIRATION 2016. [DOI: 10.1007/978-94-017-7481-9_20] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
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Hasan SS, Proctor EA, Yamashita E, Dokholyan NV, Cramer WA. Traffic within the cytochrome b6f lipoprotein complex: gating of the quinone portal. Biophys J 2015; 107:1620-8. [PMID: 25296314 DOI: 10.1016/j.bpj.2014.08.003] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/18/2014] [Revised: 07/29/2014] [Accepted: 08/05/2014] [Indexed: 12/24/2022] Open
Abstract
The cytochrome bc complexes b6f and bc1 catalyze proton-coupled quinol/quinone redox reactions to generate a transmembrane proton electrochemical gradient. Quinol oxidation on the electrochemically positive (p) interface of the complex occurs at the end of a narrow quinol/quinone entry/exit Qp portal, 11 Å long in bc complexes. Superoxide, which has multiple signaling functions, is a by-product of the p-side quinol oxidation. Although the transmembrane core and the chemistry of quinone redox reactions are conserved in bc complexes, the rate of superoxide generation is an order of magnitude greater in the b6f complex, implying that functionally significant differences in structure exist between the b6f and bc1 complexes on the p-side. A unique structure feature of the b6f p-side quinol oxidation site is the presence of a single chlorophyll-a molecule whose function is unrelated to light harvesting. This study describes a cocrystal structure of the cytochrome b6f complex with the quinol analog stigmatellin, which partitions in the Qp portal of the bc1 complex, but not effectively in b6f. It is inferred that the Qp portal is partially occluded in the b6f complex relative to bc1. Based on a discrete molecular-dynamics analysis, occlusion of the Qp portal is attributed to the presence of the chlorophyll phytyl tail, which increases the quinone residence time within the Qp portal and is inferred to be a cause of enhanced superoxide production. This study attributes a novel (to our knowledge), structure-linked function to the otherwise enigmatic chlorophyll-a in the b6f complex, which may also be relevant to intracellular redox signaling.
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Affiliation(s)
- S Saif Hasan
- Department of Biological Sciences, Hockmeyer Hall of Structural Biology, Purdue University, West Lafayette, Indiana
| | - Elizabeth A Proctor
- Curriculum in Bioinformatics and Computational Biology, University of North Carolina, Chapel Hill, North Carolina
| | - Eiki Yamashita
- Osaka University, Institute for Protein Research, Suita, Osaka, Japan
| | - Nikolay V Dokholyan
- Department of Biochemistry and Biophysics, University of North Carolina, Chapel Hill, North Carolina
| | - William A Cramer
- Department of Biological Sciences, Hockmeyer Hall of Structural Biology, Purdue University, West Lafayette, Indiana.
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Agarwal R, Hasan SS, Jones LM, Stofleth JT, Ryan CM, Whitelegge JP, Kehoe DM, Cramer WA. Role of domain swapping in the hetero-oligomeric cytochrome b6f lipoprotein complex. Biochemistry 2015; 54:3151-63. [PMID: 25928281 DOI: 10.1021/acs.biochem.5b00279] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023]
Abstract
Domain swapping that contributes to the stability of biologically crucial multisubunit complexes has been implicated in protein oligomerization. In the case of membrane protein assemblies, domain swapping of the iron-sulfur protein (ISP) subunit occurs in the hetero-oligomeric cytochrome b6f and bc1 complexes, which are organized as symmetric dimers that generate the transmembrane proton electrochemical gradient utilized for ATP synthesis. In these complexes, the ISP C-terminal predominantly β-sheet extrinsic domain containing the redox-active [2Fe-2S] cluster resides on the electrochemically positive side of each monomer in the dimeric complex. This domain is bound to the membrane sector of the complex through an N-terminal transmembrane α-helix that is "swapped' to the other monomer of the complex where it spans the complex and the membrane. Detailed analysis of the function and structure of the b6f complex isolated from the cyanobacterium Fremyella diplosiphon SF33 shows that the domain-swapped ISP structure is necessary for function but is not necessarily essential for maintenance of the dimeric structure of the complex. On the basis of crystal structures of the cytochrome complex, the stability of the cytochrome dimer is attributed to specific intermonomer protein-protein and protein-lipid hydrophobic interactions. The geometry of the domain-swapped ISP structure is proposed to be a consequence of the requirement that the anchoring helix of the ISP not perturb the heme organization or quinone channel in the conserved core of each monomer.
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Affiliation(s)
- Rachna Agarwal
- †Department of Biological Sciences, Purdue University, West Lafayette, Indiana 47907, United States
| | - S Saif Hasan
- †Department of Biological Sciences, Purdue University, West Lafayette, Indiana 47907, United States
| | - LaDonna M Jones
- ‡Department of Biology, Indiana University, Bloomington, Indiana 47405, United States
| | - Jason T Stofleth
- †Department of Biological Sciences, Purdue University, West Lafayette, Indiana 47907, United States
| | - Christopher M Ryan
- §Pasarow Mass Spectrometry Laboratory, NPI-Semel Institute, University of California, Los Angeles, California 90095, United States
| | - Julian P Whitelegge
- §Pasarow Mass Spectrometry Laboratory, NPI-Semel Institute, University of California, Los Angeles, California 90095, United States
| | - David M Kehoe
- ‡Department of Biology, Indiana University, Bloomington, Indiana 47405, United States
| | - William A Cramer
- †Department of Biological Sciences, Purdue University, West Lafayette, Indiana 47907, United States
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Internal lipid architecture of the hetero-oligomeric cytochrome b6f complex. Structure 2014; 22:1008-15. [PMID: 24931468 DOI: 10.1016/j.str.2014.05.004] [Citation(s) in RCA: 44] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/13/2014] [Revised: 05/04/2014] [Accepted: 05/06/2014] [Indexed: 12/18/2022]
Abstract
The role of lipids in the assembly, structure, and function of hetero-oligomeric membrane protein complexes is poorly understood. The dimeric photosynthetic cytochrome b6f complex, a 16-mer of eight distinct subunits and 26 transmembrane helices, catalyzes transmembrane proton-coupled electron transfer for energy storage. Using a 2.5 Å crystal structure of the dimeric complex, we identified 23 distinct lipid-binding sites per monomer. Annular lipids are proposed to provide a connection for super-complex formation with the photosystem-I reaction center and the LHCII kinase enzyme for transmembrane signaling. Internal lipids mediate crosslinking to stabilize the domain-swapped iron-sulfur protein subunit, dielectric heterogeneity within intermonomer and intramonomer electron transfer pathways, and dimer stabilization through lipid-mediated intermonomer interactions. This study provides a complete structure analysis of lipid-mediated functions in a multi-subunit membrane protein complex and reveals lipid sites at positions essential for assembly and function.
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Transmembrane signaling and assembly of the cytochrome b6f-lipidic charge transfer complex. BIOCHIMICA ET BIOPHYSICA ACTA-BIOENERGETICS 2013; 1827:1295-308. [PMID: 23507619 DOI: 10.1016/j.bbabio.2013.03.002] [Citation(s) in RCA: 49] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/17/2012] [Revised: 02/27/2013] [Accepted: 03/06/2013] [Indexed: 12/30/2022]
Abstract
Structure-function properties of the cytochrome b6f complex are sufficiently unique compared to those of the cytochrome bc1 complex that b6f should not be considered a trivially modified bc1 complex. A unique property of the dimeric b6f complex is its involvement in transmembrane signaling associated with the p-side oxidation of plastoquinol. Structure analysis of lipid binding sites in the cyanobacterial b6f complex prepared by hydrophobic chromatography shows that the space occupied by the H transmembrane helix in the cytochrome b subunit of the bc1 complex is mostly filled by a lipid in the b6f crystal structure. It is suggested that this space can be filled by the domain of a transmembrane signaling protein. The identification of lipid sites and likely function defines the intra-membrane conserved central core of the b6f complex, consisting of the seven trans-membrane helices of the cytochrome b and subunit IV polypeptides. The other six TM helices, contributed by cytochrome f, the iron-sulfur protein, and the four peripheral single span subunits, define a peripheral less conserved domain of the complex. The distribution of conserved and non-conserved domains of each monomer of the complex, and the position and inferred function of a number of the lipids, suggests a model for the sequential assembly in the membrane of the eight subunits of the b6f complex, in which the assembly is initiated by formation of the cytochrome b6-subunit IV core sub-complex in a monomer unit. Two conformations of the unique lipidic chlorophyll a, defined in crystal structures, are described, and functions of the outlying β-carotene, a possible 'latch' in supercomplex formation, are discussed. This article is part of a Special Issue entitled: Respiratory complex III and related bc complexes.
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Barber J, Horton P. Integrating current knowledge in various aspects of thylakoid membrane structure and dynamics. Philos Trans R Soc Lond B Biol Sci 2012; 367:3381-3. [PMID: 23148263 DOI: 10.1098/rstb.2012.0329] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Affiliation(s)
- James Barber
- Division of Molecular Biosciences, Department of Life Sciences, Imperial College London, London, UK
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