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Fujimoto KJ, Tsuji R, Wang-Otomo ZY, Yanai T. Prominent Role of Charge Transfer in the Spectral Tuning of Photosynthetic Light-Harvesting I Complex. ACS PHYSICAL CHEMISTRY AU 2024; 4:499-509. [PMID: 39346607 PMCID: PMC11428290 DOI: 10.1021/acsphyschemau.4c00022] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Subscribe] [Scholar Register] [Received: 03/23/2024] [Revised: 07/24/2024] [Accepted: 07/24/2024] [Indexed: 10/01/2024]
Abstract
Purple bacteria possess two ring-shaped protein complexes, light-harvesting 1 (LH1) and 2 (LH2), both of which function as antennas for solar energy utilization for photosynthesis but exhibit distinct absorption properties. The two antennas have differing amounts of bacteriochlorophyll (BChl) a; however, their significance in spectral tuning remains elusive. Here, we report a high-precision evaluation of the physicochemical factors contributing to the variation in absorption maxima between LH1 and LH2, namely, BChl a structural distortion, protein electrostatic interaction, excitonic coupling, and charge transfer (CT) effects, as derived from detailed spectral calculations using an extended version of the exciton model, in the model purple bacterium Rhodospirillum rubrum. Spectral analysis confirmed that the electronic structure of the excited state in LH1 extended to the BChl a 16-mer. Further analysis revealed that the LH1-specific redshift (∼61% in energy) is predominantly accounted for by the CT effect resulting from the closer inter-BChl distance in LH1 than in LH2. Our analysis explains how LH1 and LH2, both with chemically identical BChl a chromophores, use distinct physicochemical effects to achieve a progressive redshift from LH2 to LH1, ensuring efficient energy transfer to the reaction center special pair.
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Affiliation(s)
- Kazuhiro J. Fujimoto
- Institute
of Transformative Bio-Molecules (WPI-ITbM), Nagoya University, Furocho, Chikusa, Nagoya 464-8601, Japan
- Department
of Chemistry, Graduate School of Science, Nagoya University, Furocho, Chikusa, Nagoya 464-8601, Japan
| | - Rio Tsuji
- Department
of Chemistry, Graduate School of Science, Nagoya University, Furocho, Chikusa, Nagoya 464-8601, Japan
| | | | - Takeshi Yanai
- Institute
of Transformative Bio-Molecules (WPI-ITbM), Nagoya University, Furocho, Chikusa, Nagoya 464-8601, Japan
- Department
of Chemistry, Graduate School of Science, Nagoya University, Furocho, Chikusa, Nagoya 464-8601, Japan
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2
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Tani K, Kanno R, Ji XC, Satoh I, Kobayashi Y, Hall M, Yu LJ, Kimura Y, Mizoguchi A, Humbel BM, Madigan MT, Wang-Otomo ZY. Rhodobacter capsulatus forms a compact crescent-shaped LH1-RC photocomplex. Nat Commun 2023; 14:846. [PMID: 36792596 PMCID: PMC9932092 DOI: 10.1038/s41467-023-36460-w] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/21/2022] [Accepted: 02/01/2023] [Indexed: 02/17/2023] Open
Abstract
Rhodobacter (Rba.) capsulatus has been a favored model for studies of all aspects of bacterial photosynthesis. This purple phototroph contains PufX, a polypeptide crucial for dimerization of the light-harvesting 1-reaction center (LH1-RC) complex, but lacks protein-U, a U-shaped polypeptide in the LH1-RC of its close relative Rba. sphaeroides. Here we present a cryo-EM structure of the Rba. capsulatus LH1-RC purified by DEAE chromatography. The crescent-shaped LH1-RC exhibits a compact structure containing only 10 LH1 αβ-subunits. Four αβ-subunits corresponding to those adjacent to protein-U in Rba. sphaeroides were absent. PufX in Rba. capsulatus exhibits a unique conformation in its N-terminus that self-associates with amino acids in its own transmembrane domain and interacts with nearby polypeptides, preventing it from interacting with proteins in other complexes and forming dimeric structures. These features are discussed in relation to the minimal requirements for the formation of LH1-RC monomers and dimers, the spectroscopic behavior of both the LH1 and RC, and the bioenergetics of energy transfer from LH1 to the RC.
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Affiliation(s)
- Kazutoshi Tani
- Graduate School of Medicine, Mie University, Tsu, Japan.
| | - Ryo Kanno
- Scientific Imaging Section, Research Support Division, Okinawa Institute of Science and Technology Graduate University (OIST), 1919-1, Tancha, Onna-Son, Kunigami-Gun, Okinawa, Japan.,Quantum wave microscopy unit, Okinawa Institute of Science and Technology Graduate University (OIST), 1919-1, Tancha, Onna-Son, Kunigami-Gun, Okinawa, Japan
| | | | | | | | - Malgorzata Hall
- Scientific Imaging Section, Research Support Division, Okinawa Institute of Science and Technology Graduate University (OIST), 1919-1, Tancha, Onna-Son, Kunigami-Gun, Okinawa, Japan
| | - Long-Jiang Yu
- Photosynthesis Research Center, Key Laboratory of Photobiology, Institute of Botany, Chinese Academy of Sciences, Beijing, China
| | - Yukihiro Kimura
- Department of Agrobioscience, Graduate School of Agriculture, Kobe University, Nada, Kobe, Japan
| | | | - Bruno M Humbel
- Scientific Imaging Section, Research Support Division, Okinawa Institute of Science and Technology Graduate University (OIST), 1919-1, Tancha, Onna-Son, Kunigami-Gun, Okinawa, Japan.,Department of Cell Biology and Neuroscience, Juntendo University, Graduate School of Medicine, Tokyo, Japan
| | - Michael T Madigan
- School of Biological Sciences, Department of Microbiology, Southern Illinois University, Carbondale, IL, USA
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3
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Sutherland GA, Qian P, Hunter CN, Swainsbury DJ, Hitchcock A. Engineering purple bacterial carotenoid biosynthesis to study the roles of carotenoids in light-harvesting complexes. Methods Enzymol 2022; 674:137-184. [DOI: 10.1016/bs.mie.2022.04.001] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
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4
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Cryo-EM structure of the dimeric Rhodobacter sphaeroides RC-LH1 core complex at 2.9 Å: the structural basis for dimerisation. Biochem J 2021; 478:3923-3937. [PMID: 34622934 PMCID: PMC8652583 DOI: 10.1042/bcj20210696] [Citation(s) in RCA: 19] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/20/2021] [Revised: 10/07/2021] [Accepted: 10/07/2021] [Indexed: 11/23/2022]
Abstract
The dimeric reaction centre light-harvesting 1 (RC-LH1) core complex of Rhodobacter sphaeroides converts absorbed light energy to a charge separation, and then it reduces a quinone electron and proton acceptor to a quinol. The angle between the two monomers imposes a bent configuration on the dimer complex, which exerts a major influence on the curvature of the membrane vesicles, known as chromatophores, where the light-driven photosynthetic reactions take place. To investigate the dimerisation interface between two RC-LH1 monomers, we determined the cryogenic electron microscopy structure of the dimeric complex at 2.9 Å resolution. The structure shows that each monomer consists of a central RC partly enclosed by a 14-subunit LH1 ring held in an open state by PufX and protein-Y polypeptides, thus enabling quinones to enter and leave the complex. Two monomers are brought together through N-terminal interactions between PufX polypeptides on the cytoplasmic side of the complex, augmented by two novel transmembrane polypeptides, designated protein-Z, that bind to the outer faces of the two central LH1 β polypeptides. The precise fit at the dimer interface, enabled by PufX and protein-Z, by C-terminal interactions between opposing LH1 αβ subunits, and by a series of interactions with a bound sulfoquinovosyl diacylglycerol lipid, bring together each monomer creating an S-shaped array of 28 bacteriochlorophylls. The seamless join between the two sets of LH1 bacteriochlorophylls provides a path for excitation energy absorbed by one half of the complex to migrate across the dimer interface to the other half.
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5
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Cryo-EM structure of the monomeric Rhodobacter sphaeroides RC-LH1 core complex at 2.5 Å. Biochem J 2021; 478:3775-3790. [PMID: 34590677 PMCID: PMC8589327 DOI: 10.1042/bcj20210631] [Citation(s) in RCA: 26] [Impact Index Per Article: 8.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/23/2021] [Revised: 09/22/2021] [Accepted: 09/30/2021] [Indexed: 12/02/2022]
Abstract
Reaction centre light-harvesting 1 (RC–LH1) complexes are the essential components of bacterial photosynthesis. The membrane-intrinsic LH1 complex absorbs light and the energy migrates to an enclosed RC where a succession of electron and proton transfers conserves the energy as a quinol, which is exported to the cytochrome bc1 complex. In some RC–LH1 variants quinols can diffuse through small pores in a fully circular, 16-subunit LH1 ring, while in others missing LH1 subunits create a gap for quinol export. We used cryogenic electron microscopy to obtain a 2.5 Å resolution structure of one such RC–LH1, a monomeric complex from Rhodobacter sphaeroides. The structure shows that the RC is partly enclosed by a 14-subunit LH1 ring in which each αβ heterodimer binds two bacteriochlorophylls and, unusually for currently reported complexes, two carotenoids rather than one. Although the extra carotenoids confer an advantage in terms of photoprotection and light harvesting, they could impede passage of quinones through small, transient pores in the LH1 ring, necessitating a mechanism to create a dedicated quinone channel. The structure shows that two transmembrane proteins play a part in stabilising an open ring structure; one of these components, the PufX polypeptide, is augmented by a hitherto undescribed protein subunit we designate as protein-Y, which lies against the transmembrane regions of the thirteenth and fourteenth LH1α polypeptides. Protein-Y prevents LH1 subunits 11–14 adjacent to the RC QB site from bending inwards towards the RC and, with PufX preventing complete encirclement of the RC, this pair of polypeptides ensures unhindered quinone diffusion.
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Swainsbury DJK, Qian P, Jackson PJ, Faries KM, Niedzwiedzki DM, Martin EC, Farmer DA, Malone LA, Thompson RF, Ranson NA, Canniffe DP, Dickman MJ, Holten D, Kirmaier C, Hitchcock A, Hunter CN. Structures of Rhodopseudomonas palustris RC-LH1 complexes with open or closed quinone channels. SCIENCE ADVANCES 2021; 7:7/3/eabe2631. [PMID: 33523887 PMCID: PMC7806223 DOI: 10.1126/sciadv.abe2631] [Citation(s) in RCA: 17] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/10/2020] [Accepted: 11/18/2020] [Indexed: 05/23/2023]
Abstract
The reaction-center light-harvesting complex 1 (RC-LH1) is the core photosynthetic component in purple phototrophic bacteria. We present two cryo-electron microscopy structures of RC-LH1 complexes from Rhodopseudomonas palustris A 2.65-Å resolution structure of the RC-LH114-W complex consists of an open 14-subunit LH1 ring surrounding the RC interrupted by protein-W, whereas the complex without protein-W at 2.80-Å resolution comprises an RC completely encircled by a closed, 16-subunit LH1 ring. Comparison of these structures provides insights into quinone dynamics within RC-LH1 complexes, including a previously unidentified conformational change upon quinone binding at the RC QB site, and the locations of accessory quinone binding sites that aid their delivery to the RC. The structurally unique protein-W prevents LH1 ring closure, creating a channel for accelerated quinone/quinol exchange.
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Affiliation(s)
- David J K Swainsbury
- Department of Molecular Biology and Biotechnology, University of Sheffield, Sheffield, S10 2TN, UK.
| | - Pu Qian
- Department of Molecular Biology and Biotechnology, University of Sheffield, Sheffield, S10 2TN, UK
- Materials and Structural Analysis, Thermo Fisher Scientific, Achtseweg Noord 5, 5651 GG Eindhoven, Netherlands
| | - Philip J Jackson
- Department of Molecular Biology and Biotechnology, University of Sheffield, Sheffield, S10 2TN, UK
- Department of Chemical and Biological Engineering, University of Sheffield, Sheffield, S1 3JD, UK
| | - Kaitlyn M Faries
- Department of Chemistry, Washington University in St. Louis, St. Louis, MO 63130, USA
| | - Dariusz M Niedzwiedzki
- Center for Solar Energy and Energy Storage, Washington University in St. Louis, St. Louis, MO 63130, USA
- Department of Energy, Environmental and Chemical Engineering, Washington University in St. Louis, St. Louis, MO 63130, USA
| | - Elizabeth C Martin
- Department of Molecular Biology and Biotechnology, University of Sheffield, Sheffield, S10 2TN, UK
| | - David A Farmer
- Department of Molecular Biology and Biotechnology, University of Sheffield, Sheffield, S10 2TN, UK
| | - Lorna A Malone
- Department of Molecular Biology and Biotechnology, University of Sheffield, Sheffield, S10 2TN, UK
| | - Rebecca F Thompson
- Astbury Centre for Structural Molecular Biology, School of Molecular and Cellular Biology, University of Leeds, Leeds, LS2 9JT, UK
| | - Neil A Ranson
- Astbury Centre for Structural Molecular Biology, School of Molecular and Cellular Biology, University of Leeds, Leeds, LS2 9JT, UK
| | - Daniel P Canniffe
- Department of Biochemistry and Systems Biology, Institute of Systems, Molecular and Integrative Biology, University of Liverpool, Liverpool, L69 7ZB, UK
| | - Mark J Dickman
- Department of Chemical and Biological Engineering, University of Sheffield, Sheffield, S1 3JD, UK
| | - Dewey Holten
- Department of Chemistry, Washington University in St. Louis, St. Louis, MO 63130, USA
| | - Christine Kirmaier
- Department of Chemistry, Washington University in St. Louis, St. Louis, MO 63130, USA
| | - 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.
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7
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Qian P, Siebert CA, Wang P, Canniffe DP, Hunter CN. Cryo-EM structure of the
Blastochloris viridis LH1–RC complex at 2.9 Å. Nature 2018; 556:203-208. [DOI: 10.1038/s41586-018-0014-5] [Citation(s) in RCA: 65] [Impact Index Per Article: 10.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/26/2017] [Accepted: 02/02/2018] [Indexed: 11/09/2022]
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Swainsbury DJK, Scheidelaar S, Foster N, van Grondelle R, Killian JA, Jones MR. The effectiveness of styrene-maleic acid (SMA) copolymers for solubilisation of integral membrane proteins from SMA-accessible and SMA-resistant membranes. BIOCHIMICA ET BIOPHYSICA ACTA. BIOMEMBRANES 2017; 1859:2133-2143. [PMID: 28751090 PMCID: PMC5593810 DOI: 10.1016/j.bbamem.2017.07.011] [Citation(s) in RCA: 56] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 03/18/2017] [Revised: 07/14/2017] [Accepted: 07/23/2017] [Indexed: 11/27/2022]
Abstract
Solubilisation of biological lipid bilayer membranes for analysis of their protein complement has traditionally been carried out using detergents, but there is increasing interest in the use of amphiphilic copolymers such as styrene maleic acid (SMA) for the solubilisation, purification and characterisation of integral membrane proteins in the form of protein/lipid nanodiscs. Here we survey the effectiveness of various commercially-available formulations of the SMA copolymer in solubilising Rhodobacter sphaeroides reaction centres (RCs) from photosynthetic membranes. We find that formulations of SMA with a 2:1 or 3:1 ratio of styrene to maleic acid are almost as effective as detergent in solubilising RCs, with the best solubilisation by short chain variants (<30kDa weight average molecular weight). The effectiveness of 10kDa 2:1 and 3:1 formulations of SMA to solubilise RCs gradually declined when genetically-encoded coiled-coil bundles were used to artificially tether normally monomeric RCs into dimeric, trimeric and tetrameric multimers. The ability of SMA to solubilise reaction centre-light harvesting 1 (RC-LH1) complexes from densely packed and highly ordered photosynthetic membranes was uniformly low, but could be increased through a variety of treatments to increase the lipid:protein ratio. However, proteins isolated from such membranes comprised clusters of complexes in small membrane patches rather than individual proteins. We conclude that short-chain 2:1 and 3:1 formulations of SMA are the most effective in solubilising integral membrane proteins, but that solubilisation efficiencies are strongly influenced by the size of the target protein and the density of packing of proteins in the membrane.
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Affiliation(s)
- David J K Swainsbury
- School of Biochemistry, University of Bristol, Biomedical Sciences Building, University Walk, Bristol BS8 1TD, United Kingdom
| | - Stefan Scheidelaar
- Membrane Biochemistry & Biophysics, Utrecht University, Bijvoet Center for Biomolecular Research, Utrecht, The Netherlands
| | - Nicholas Foster
- School of Biochemistry, University of Bristol, Biomedical Sciences Building, University Walk, Bristol BS8 1TD, United Kingdom
| | - Rienk van Grondelle
- Division of Physics and Astronomy, VU University Amsterdam, De Boelelaan 1081, Amsterdam 1081 HV, The Netherlands
| | - J Antoinette Killian
- Membrane Biochemistry & Biophysics, Utrecht University, Bijvoet Center for Biomolecular Research, Utrecht, The Netherlands
| | - Michael R Jones
- School of Biochemistry, University of Bristol, Biomedical Sciences Building, University Walk, Bristol BS8 1TD, United Kingdom.
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9
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Swainsbury DJK, Martin EC, Vasilev C, Parkes-Loach PS, Loach PA, Neil Hunter C. Engineering of a calcium-ion binding site into the RC-LH1-PufX complex of Rhodobacter sphaeroides to enable ion-dependent spectral red-shifting. BIOCHIMICA ET BIOPHYSICA ACTA-BIOENERGETICS 2017; 1858:927-938. [PMID: 28826909 PMCID: PMC5604489 DOI: 10.1016/j.bbabio.2017.08.009] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 06/26/2017] [Revised: 08/02/2017] [Accepted: 08/17/2017] [Indexed: 01/01/2023]
Abstract
The reaction centre-light harvesting 1 (RC-LH1) complex of Thermochromatium (Tch.) tepidum has a unique calcium-ion binding site that enhances thermal stability and red-shifts the absorption of LH1 from 880nm to 915nm in the presence of calcium-ions. The LH1 antenna of mesophilic species of phototrophic bacteria such as Rhodobacter (Rba.) sphaeroides does not possess such properties. We have engineered calcium-ion binding into the LH1 antenna of Rba. sphaeroides by progressively modifying the native LH1 polypeptides with sequences from Tch. tepidum. We show that acquisition of the C-terminal domains from LH1 α and β of Tch. tepidum is sufficient to activate calcium-ion binding and the extent of red-shifting increases with the proportion of Tch. tepidum sequence incorporated. However, full exchange of the LH1 polypeptides with those of Tch. tepidum results in misassembled core complexes. Isolated α and β polypeptides from our most successful mutant were reconstituted in vitro with BChl a to form an LH1-type complex, which was stabilised 3-fold by calcium-ions. Additionally, carotenoid specificity was changed from spheroidene found in Rba. sphaeroides to spirilloxanthin found in Tch. tepidum, with the latter enhancing in vitro formation of LH1. These data show that the C-terminal LH1 α/β domains of Tch. tepidum behave autonomously, and are able to transmit calcium-ion induced conformational changes to BChls bound to the rest of a foreign antenna complex. Thus, elements of foreign antenna complexes, such as calcium-ion binding and blue/red switching of absorption, can be ported into Rhodobacter sphaeroides using careful design processes.
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Affiliation(s)
- David J K Swainsbury
- Department of Molecular Biology and Biotechnology, University of Sheffield, Firth Court, Western Bank, Sheffield, S10 2TN, United Kingdom.
| | - Elizabeth C Martin
- Department of Molecular Biology and Biotechnology, University of Sheffield, Firth Court, Western Bank, Sheffield, S10 2TN, United Kingdom
| | - Cvetelin Vasilev
- Department of Molecular Biology and Biotechnology, University of Sheffield, Firth Court, Western Bank, Sheffield, S10 2TN, United Kingdom
| | - Pamela S Parkes-Loach
- Department of Molecular Biosciences, Northwestern University, Hogan 2100, 2205 Tech Drive, Evanston, IL 60208, United States
| | - Paul A Loach
- Department of Molecular Biosciences, Northwestern University, Hogan 2100, 2205 Tech Drive, Evanston, IL 60208, United States
| | - C Neil Hunter
- Department of Molecular Biology and Biotechnology, University of Sheffield, Firth Court, Western Bank, Sheffield, S10 2TN, United Kingdom
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The C-terminus of PufX plays a key role in dimerisation and assembly of the reaction center light-harvesting 1 complex from Rhodobacter sphaeroides. BIOCHIMICA ET BIOPHYSICA ACTA-BIOENERGETICS 2017; 1858:795-803. [PMID: 28587931 PMCID: PMC5538271 DOI: 10.1016/j.bbabio.2017.06.001] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 02/24/2017] [Revised: 05/31/2017] [Accepted: 06/01/2017] [Indexed: 11/22/2022]
Abstract
In bacterial photosynthesis reaction center-light-harvesting 1 (RC-LH1) complexes trap absorbed solar energy by generating a charge separated state. Subsequent electron and proton transfers form a quinol, destined to diffuse to the cytochrome bc1 complex. In bacteria such as Rhodobacter (Rba.) sphaeroides and Rba. capsulatus the PufX polypeptide creates a channel for quinone/quinol traffic across the LH1 complex that surrounds the RC, and it is therefore essential for photosynthetic growth. PufX also plays a key role in dimerization of the RC-LH1-PufX core complex, and the structure of the Rba. sphaeroides complex shows that the PufX C-terminus, particularly the region from X49-X53, likely mediates association of core monomers. To investigate this putative interaction we analysed mutations PufX R49L, PufX R53L, PufX R49/53L and PufX G52L by measuring photosynthetic growth, fractionation of detergent-solubilised membranes, formation of 2-D crystals and electron microscopy. We show that these mutations do not affect assembly of PufX within the core or photosynthetic growth but they do prevent dimerization, consistent with predictions from the RC-LH1-PufX structure. We obtained low resolution structures of monomeric core complexes with and without PufX, using electron microscopy of negatively stained single particles and 3D reconstruction; the monomeric complex with PufX corresponds to one half of the dimer structure whereas LH1 completely encloses the RC if the gene encoding PufX is deleted. On the basis of the insights gained from these mutagenesis and structural analyses we propose a sequence for assembly of the dimeric RC-LH1-PufX complex.
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Niederman RA. Development and dynamics of the photosynthetic apparatus in purple phototrophic bacteria. BIOCHIMICA ET BIOPHYSICA ACTA-BIOENERGETICS 2015; 1857:232-46. [PMID: 26519773 DOI: 10.1016/j.bbabio.2015.10.014] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/22/2015] [Revised: 10/22/2015] [Accepted: 10/25/2015] [Indexed: 11/30/2022]
Abstract
The purple bacterium Rhodobacter sphaeroides provides a useful model system for studies of the assembly and dynamics of bacterial photosynthetic membranes. For the nascent developing membrane, proteomic analyses showed an ~2-fold enrichment in general membrane assembly factors, compared to chromatophores. When the protonophore carbonyl-cyanide m-chlorophenyl-hydrazone (CCCP) was added to an ICM inducing culture, an ~2-fold elevation in spectral counts vs. the control was seen for the SecA translocation ATPase, the preprotein translocase SecY, SecD and SecF insertion components, and chaperonins DnaJ and DnaK, which act early in the assembly process. It is suggested that these factors accumulated with their nascent polypeptides, as putative assembly intermediates in a functionally arrested state. Since in Synechocystis PCC 6803, a link has been established between Chl delivery involving the high-light HilD protein and the SecY/YidC-requiring cotranslational insertion of nascent polypeptides, such a connection between BChl biosynthesis and insertion and folding of nascent Rba. sphaeroides BChl binding proteins is likely to also occur. AFM imaging studies of the formation of the reaction center (RC)-light harvesting 1 (LH1) complex suggested a cooperative assembly mechanism in which, following the association between the RC template and the initial LH1 unit, addition of successive LH1 units to the RC drives the assembly process to completion. Alterations in membrane dynamics as the developing membrane becomes filled with LH2-rings were assessed by fluorescence induction/relaxation kinetics, which showed a slowing in RC electron transfer rate thought to mainly reflect alterations in donor side electron transfer. This was attributed to an increased distance for electron flow in cytochrome c2 between the RC and cytochrome bc1 complexes, as suggested in the current structural models. This article is part of a Special Issue entitled Organization and dynamics of bioenergetic systems in bacteria, edited by Prof Conrad Mullineaux.
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Affiliation(s)
- Robert A Niederman
- Department of Molecular Biology and Biochemistry, Rutgers, The State University of New Jersey, 604 Allison Road, Piscataway, New Jersey 08854-8082, United States.
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12
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Patole S, Vasilev C, El-Zubir O, Wang L, Johnson MP, Cadby AJ, Leggett GJ, Hunter CN. Interference lithographic nanopatterning of plant and bacterial light-harvesting complexes on gold substrates. Interface Focus 2015; 5:20150005. [PMID: 26464784 PMCID: PMC4590419 DOI: 10.1098/rsfs.2015.0005] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/16/2023] Open
Abstract
We describe a facile approach for nanopatterning of photosynthetic light-harvesting complexes over macroscopic areas, and use optical spectroscopy to demonstrate retention of native properties by both site-specifically and non-specifically attached photosynthetic membrane proteins. A Lloyd's mirror dual-beam interferometer was used to expose self-assembled monolayers of amine-terminated alkylthiolates on gold to laser irradiation. Following exposure, photo-oxidized adsorbates were replaced by oligo(ethylene glycol) terminated thiols, and the remaining intact amine-functionalized regions were used for attachment of the major light-harvesting chlorophyll-protein complex from plants, LHCII. These amine patterns could be derivatized with nitrilotriacetic acid (NTA), so that polyhistidine-tagged bacteriochlorophyll-protein complexes from phototrophic bacteria could be attached with a defined surface orientation. By varying parameters such as the angle between the interfering beams and the laser irradiation dose, it was possible to vary the period and widths of NTA and amine-functionalized lines on the surfaces; periods varied from 1200 to 240 nm and linewidths as small as 60 nm (λ/4) were achieved. This level of control over the surface chemistry was reflected in the surface topology of the protein nanostructures imaged by atomic force microscopy; fluorescence imaging and spectral measurements demonstrated that the surface-attached proteins had retained their native functionality.
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Affiliation(s)
- Samson Patole
- Department of Chemistry, University of Sheffield, Brook Hill, Sheffield S3 7HF, UK
- Department of Molecular Biology and Biotechnology, University of Sheffield, Western Bank, Sheffield S10 2TN, UK
| | - Cvetelin Vasilev
- Department of Molecular Biology and Biotechnology, University of Sheffield, Western Bank, Sheffield S10 2TN, UK
| | - Osama El-Zubir
- Department of Chemistry, University of Sheffield, Brook Hill, Sheffield S3 7HF, UK
| | - Lin Wang
- Department of Molecular Biology and Biotechnology, University of Sheffield, Western Bank, Sheffield S10 2TN, UK
- Department of Physics and Astronomy, University of Sheffield, Hicks Building, Hounsfield Road, Sheffield S3 7RH, UK
| | - Matthew P. Johnson
- Department of Molecular Biology and Biotechnology, University of Sheffield, Western Bank, Sheffield S10 2TN, UK
| | - Ashley J. Cadby
- Department of Physics and Astronomy, University of Sheffield, Hicks Building, Hounsfield Road, Sheffield S3 7RH, UK
| | - Graham J. Leggett
- Department of Chemistry, University of Sheffield, Brook Hill, Sheffield S3 7HF, UK
| | - C. Neil Hunter
- Department of Molecular Biology and Biotechnology, University of Sheffield, Western Bank, Sheffield S10 2TN, UK
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Olsen JD, Adams PG, Jackson PJ, Dickman MJ, Qian P, Hunter CN. Aberrant assembly complexes of the reaction center light-harvesting 1 PufX (RC-LH1-PufX) core complex of Rhodobacter sphaeroides imaged by atomic force microscopy. J Biol Chem 2014; 289:29927-36. [PMID: 25193660 PMCID: PMC4208002 DOI: 10.1074/jbc.m114.596585] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/17/2023] Open
Abstract
In the purple phototrophic bacterium Rhodobacter sphaeroides, many protein complexes congregate within the membrane to form operational photosynthetic units consisting of arrays of light-harvesting LH2 complexes and monomeric and dimeric reaction center (RC)-light-harvesting 1 (LH1)-PufX “core” complexes. Each half of a dimer complex consists of a RC surrounded by 14 LH1 αβ subunits, with two bacteriochlorophylls (Bchls) sandwiched between each αβ pair of transmembrane helices. We used atomic force microscopy (AFM) to investigate the assembly of single molecules of the RC-LH1-PufX complex using membranes prepared from LH2-minus mutants. When the RC and PufX components were also absent, AFM revealed a series of LH1 variants where the repeating α1β1(Bchl)2 units had formed rings of variable size, ellipses, and spirals and also arcs that could be assembly products. The spiral complexes occur when the LH1 ring has failed to close, and short arcs are suggestive of prematurely terminated LH1 complex assembly. In the absence of RCs, we occasionally observed captive proteins enclosed by the LH1 ring. When production of LH1 units was restricted by lowering the relative levels of the cognate pufBA transcript, we imaged a mixture of complete RC-LH1 core complexes, empty LH1 rings, and isolated RCs, leading us to conclude that once a RC associates with the first α1β1(Bchl)2 subunit, cooperative associations between subsequent subunits and the RC tend to drive LH1 ring assembly to completion.
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Affiliation(s)
- John D Olsen
- From the Department of Molecular Biology and Biotechnology, University of Sheffield, Sheffield, S10 2TN, United Kingdom and
| | - Peter G Adams
- From the Department of Molecular Biology and Biotechnology, University of Sheffield, Sheffield, S10 2TN, United Kingdom and
| | - Philip J Jackson
- From the Department of Molecular Biology and Biotechnology, University of Sheffield, Sheffield, S10 2TN, United Kingdom and the Department of Chemical and Biological Engineering, ChELSI Institute, University of Sheffield, Sheffield, S1 3JD, United Kingdom
| | - Mark J Dickman
- the Department of Chemical and Biological Engineering, ChELSI Institute, University of Sheffield, Sheffield, S1 3JD, United Kingdom
| | - Pu Qian
- From the Department of Molecular Biology and Biotechnology, University of Sheffield, Sheffield, S10 2TN, United Kingdom and
| | - C Neil Hunter
- From the Department of Molecular Biology and Biotechnology, University of Sheffield, Sheffield, S10 2TN, United Kingdom and
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14
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D'Haene SE, Crouch LI, Jones MR, Frese RN. Organization in photosynthetic membranes of purple bacteria in vivo: the role of carotenoids. BIOCHIMICA ET BIOPHYSICA ACTA-BIOENERGETICS 2014; 1837:1665-73. [PMID: 25017691 DOI: 10.1016/j.bbabio.2014.07.003] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/26/2014] [Revised: 07/01/2014] [Accepted: 07/03/2014] [Indexed: 11/19/2022]
Abstract
Photosynthesis in purple bacteria is performed by pigment-protein complexes that are closely packed within specialized intracytoplasmic membranes. Here we report on the influence of carotenoid composition on the organization of RC-LH1 pigment-protein complexes in intact membranes and cells of Rhodobacter sphaeroides. Mostly dimeric RC-LH1 complexes could be isolated from strains expressing native brown carotenoids when grown under illuminated/anaerobic conditions, or from strains expressing green carotenoids when grown under either illuminated/anaerobic or dark/semiaerobic conditions. However, mostly monomeric RC-LH1 complexes were isolated from strains expressing the native photoprotective red carotenoid spheroidenone, which is synthesized during phototrophic growth in the presence of oxygen. Despite this marked difference, linear dichroism (LD) and light-minus-dark LD spectra of oriented intact intracytoplasmic membranes indicated that RC-LH1 complexes are always assembled in ordered arrays, irrespective of variations in the relative amounts of isolated dimeric and monomeric RC-LH1 complexes. We propose that part of the photoprotective response to the presence of oxygen mediated by synthesis of spheroidenone may be a switch of the structure of the RC-LH1 complex from dimers to monomers, but that these monomers are still organized into the photosynthetic membrane in ordered arrays. When levels of the dimeric RC-LH1 complex were very high, and in the absence of LH2, LD and ∆LD spectra from intact cells indicated an ordered arrangement of RC-LH1 complexes. Such a degree of ordering implies the presence of highly elongated, tubular membranes with dimensions requiring orientation along the length of the cell and in a proportion larger than previously observed.
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Affiliation(s)
- Sandrine E D'Haene
- Biophysics of photosynthesis/Physics of Energy, Department of Physics and Astronomy, Faculty of Sciences, VU University Amsterdam, De Boelelaan 1081, Amsterdam 1081 HV, The Netherlands.
| | - Lucy I Crouch
- School of Biochemistry, Medical Sciences Building, University of Bristol, University Walk, Bristol BS8 1TD, United Kingdom
| | - Michael R Jones
- School of Biochemistry, Medical Sciences Building, University of Bristol, University Walk, Bristol BS8 1TD, United Kingdom.
| | - Raoul N Frese
- Biophysics of photosynthesis/Physics of Energy, Department of Physics and Astronomy, Faculty of Sciences, VU University Amsterdam, De Boelelaan 1081, Amsterdam 1081 HV, The Netherlands.
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15
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Sznee K, Crouch LI, Jones MR, Dekker JP, Frese RN. Variation in supramolecular organisation of the photosynthetic membrane of Rhodobacter sphaeroides induced by alteration of PufX. PHOTOSYNTHESIS RESEARCH 2014; 119:243-256. [PMID: 24197265 DOI: 10.1007/s11120-013-9949-4] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/11/2013] [Accepted: 10/24/2013] [Indexed: 06/02/2023]
Abstract
In purple bacteria of the genus Rhodobacter (Rba.), an LH1 antenna complex surrounds the photochemical reaction centre (RC) with a PufX protein preventing the LH1 complex from completely encircling the RC. In membranes of Rba. sphaeroides, RC-LH1 complexes associate as dimers which in turn assemble into longer range ordered arrays. The present work uses linear dichroism (LD) and dark-minus-light difference LD (ΔLD) to probe the organisation of genetically altered RC-LH1 complexes in intact membranes. The data support previous proposals that Rba. capsulatus, and Rba. sphaeroides heterologously expressing the PufX protein from Rba. capsulatus, produce monomeric core complexes in membranes that lack long-range order. Similarly, Rba. sphaeroides with a point mutation in the Gly 51 residue of PufX, which is located on the membrane-periplasm interface, assembles mainly non-ordered RC-LH1 complexes that are most likely monomeric. All the Rba. sphaeroides membranes in their ΔLD spectra exhibited a spectral fingerprint of small degree of organisation implying the possibility of ordering influence of LH1, and leading to an important conclusion that PufX itself has no influence on ordering RC-LH1 complexes, as long-range order appears to be induced only through its role of configuring RC-LH1 complexes into dimers.
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Affiliation(s)
- Kinga Sznee
- Division of Physics and Astronomy, Faculty of Sciences, VU University Amsterdam, De Boelelaan 1081, 1081 HV, Amsterdam, The Netherlands,
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16
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Taniguchi M, Du H, Lindsey JS. Enumeration of virtual libraries of combinatorial modular macrocyclic (bracelet, necklace) architectures and their linear counterparts. J Chem Inf Model 2013; 53:2203-16. [PMID: 23944229 DOI: 10.1021/ci400175f] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Abstract
A wide variety of cyclic molecular architectures are built of modular subunits and can be formed combinatorially. The mathematics for enumeration of such objects is well-developed yet lacks key features of importance in chemistry, such as specifying (i) the structures of individual members among a set of isomers, (ii) the distribution (i.e., relative amounts) of products, and (iii) the effect of nonequal ratios of reacting monomers on the product distribution. Here, a software program (Cyclaplex) has been developed to determine the number, identity (including isomers), and relative amounts of linear and cyclic architectures from a given number and ratio of reacting monomers. The program includes both mathematical formulas and generative algorithms for enumeration; the latter go beyond the former to provide desired molecular-relevant information and data-mining features. The program is equipped to enumerate four types of architectures: (i) linear architectures with directionality (macroscopic equivalent = electrical extension cords), (ii) linear architectures without directionality (batons), (iii) cyclic architectures with directionality (necklaces), and (iv) cyclic architectures without directionality (bracelets). The program can be applied to cyclic peptides, cycloveratrylenes, cyclens, calixarenes, cyclodextrins, crown ethers, cucurbiturils, annulenes, expanded meso-substituted porphyrin(ogen)s, and diverse supramolecular (e.g., protein) assemblies. The size of accessible architectures encompasses up to 12 modular subunits derived from 12 reacting monomers or larger architectures (e.g. 13-17 subunits) from fewer types of monomers (e.g. 2-4). A particular application concerns understanding the possible heterogeneity of (natural or biohybrid) photosynthetic light-harvesting oligomers (cyclic, linear) formed from distinct peptide subunits.
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Affiliation(s)
- Masahiko Taniguchi
- Department of Chemistry, North Carolina State University , Raleigh, North Carolina 27695, United States
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17
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Harrold JW, Woronowicz K, Lamptey JL, Awong J, Baird J, Moshar A, Vittadello M, Falkowski PG, Niederman RA. Functional Interfacing of Rhodospirillum rubrum Chromatophores to a Conducting Support for Capture and Conversion of Solar Energy. J Phys Chem B 2013; 117:11249-59. [DOI: 10.1021/jp402108s] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- John W. Harrold
- Department of Chemistry and Chemical
Biology, Rutgers, The State University of New Jersey, 610 Taylor Road, Piscataway, New Jersey
08854, United States
| | - Kamil Woronowicz
- Department of Molecular Biology and Biochemistry, Rutgers, The State University of New Jersey, 604 Allison
Road, Piscataway, New Jersey 08854-8082, United States
| | - Joana L. Lamptey
- Department of Molecular Biology and Biochemistry, Rutgers, The State University of New Jersey, 604 Allison
Road, Piscataway, New Jersey 08854-8082, United States
| | - John Awong
- Energy Nanotechnology and Materials
Chemistry Lab, Medgar Evers College of the City University of New York, 1638 Bedford Avenue, Brooklyn, New York 11225, United States
| | - James Baird
- Energy Nanotechnology and Materials
Chemistry Lab, Medgar Evers College of the City University of New York, 1638 Bedford Avenue, Brooklyn, New York 11225, United States
| | - Amir Moshar
- Asylum Research, 6310 Hollister Avenue, Santa Barbara, California 93117, United
States
| | - Michele Vittadello
- Energy Nanotechnology and Materials
Chemistry Lab, Medgar Evers College of the City University of New York, 1638 Bedford Avenue, Brooklyn, New York 11225, United States
| | - Paul G. Falkowski
- Department of Chemistry and Chemical
Biology, Rutgers, The State University of New Jersey, 610 Taylor Road, Piscataway, New Jersey
08854, United States
- Institute for Marine
and Coastal Sciences, Rutgers, The State University of New Jersey, 71 Dudley Road, New Brunswick, New Jersey
08901, United States
| | - Robert A. Niederman
- Department of Molecular Biology and Biochemistry, Rutgers, The State University of New Jersey, 604 Allison
Road, Piscataway, New Jersey 08854-8082, United States
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18
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Springer JW, Parkes-Loach PS, Reddy KR, Krayer M, Jiao J, Lee GM, Niedzwiedzki DM, Harris MA, Kirmaier C, Bocian DF, Lindsey JS, Holten D, Loach PA. Biohybrid Photosynthetic Antenna Complexes for Enhanced Light-Harvesting. J Am Chem Soc 2012; 134:4589-99. [DOI: 10.1021/ja207390y] [Citation(s) in RCA: 81] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
| | - Pamela S. Parkes-Loach
- Department
of Molecular Biosciences, Northwestern University, Evanston, Illinois 60208-3500,
United States
| | - Kanumuri Ramesh Reddy
- Department
of Chemistry, North Carolina State University, Raleigh, North Carolina
27695-8204, United States
| | - Michael Krayer
- Department
of Chemistry, North Carolina State University, Raleigh, North Carolina
27695-8204, United States
| | - Jieying Jiao
- Department of Chemistry, University of California, Riverside, California 92521-0403,
United States
| | - Gregory M. Lee
- Department
of Molecular Biosciences, Northwestern University, Evanston, Illinois 60208-3500,
United States
| | | | | | | | - David F. Bocian
- Department of Chemistry, University of California, Riverside, California 92521-0403,
United States
| | - Jonathan S. Lindsey
- Department
of Chemistry, North Carolina State University, Raleigh, North Carolina
27695-8204, United States
| | | | - Paul A. Loach
- Department
of Molecular Biosciences, Northwestern University, Evanston, Illinois 60208-3500,
United States
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19
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Crouch LI, Jones MR. Cross-species investigation of the functions of the Rhodobacter PufX polypeptide and the composition of the RC-LH1 core complex. BIOCHIMICA ET BIOPHYSICA ACTA-BIOENERGETICS 2011; 1817:336-52. [PMID: 22079525 DOI: 10.1016/j.bbabio.2011.10.009] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/09/2011] [Revised: 10/24/2011] [Accepted: 10/27/2011] [Indexed: 10/15/2022]
Abstract
In well-characterised species of the Rhodobacter (Rba.) genus of purple photosynthetic bacteria it is known that the photochemical reaction centre (RC) is intimately-associated with an encircling LH1 antenna pigment protein, and this LH1 antenna is prevented from completely surrounding the RC by a single copy of the PufX protein. In Rba. veldkampii only monomeric RC-LH1 complexes are assembled in the photosynthetic membrane, whereas in Rba. sphaeroides and Rba. blasticus a dimeric form is also assembled in which two RCs are surrounded by an S-shaped LH1 antenna. The present work established that dimeric RC-LH1 complexes can also be isolated from Rba. azotoformans and Rba. changlensis, but not from Rba. capsulatus or Rba. vinaykumarii. The compositions of the monomers and dimers isolated from these four species of Rhodobacter were similar to those of the well-characterised RC-LH1 complexes present in Rba. sphaeroides. Pigment proteins were also isolated from strains of Rba. sphaeroides expressing chimeric RC-LH1 complexes. Replacement of either the Rba. sphaeroides LH1 antenna or PufX with its counterpart from Rba. capsulatus led to a loss of the dimeric form of the RC-LH1 complex, but the monomeric form had a largely unaltered composition, even in strains in which the expression level of LH1 relative to the RC was reduced. The chimeric RC-LH1 complexes were also functional, supporting bacterial growth under photosynthetic conditions. The findings help to tease apart the different functions of PufX in different species of Rhodobacter, and a specific protein structural arrangement that allows PufX to fulfil these three functions is proposed.
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20
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Ng IW, Adams PG, Mothersole DJ, Vasilev C, Martin EC, Lang HP, Tucker JD, Neil Hunter C. Carotenoids are essential for normal levels of dimerisation of the RC-LH1-PufX core complex of Rhodobacter sphaeroides: characterisation of R-26 as a crtB (phytoene synthase) mutant. BIOCHIMICA ET BIOPHYSICA ACTA 2011; 1807:1056-63. [PMID: 21651888 DOI: 10.1016/j.bbabio.2011.05.020] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/11/2011] [Revised: 05/18/2011] [Accepted: 05/23/2011] [Indexed: 02/02/2023]
Abstract
Carotenoids play important roles in photosynthesis where they are involved in light-harvesting, in photo-protection and in the assembly and structural stability of light-harvesting and reaction centre complexes. In order to examine the effects of carotenoids on the oligomeric state of the reaction centre-light-harvesting 1 -PufX (RC-LH1-PufX) core complex of Rhodobacter sphaeroides two carotenoid-less mutants, TC70 and R-26, were studied. Detergent fractionation showed that in the absence of carotenoids LH2 complexes do not assemble, as expected, but also that core complexes are predominantly found as monomers, although levels of the PufX polypeptide appeared to be unaffected. Analysis of R-26 membranes by electron microscopy and atomic force microscopy reveals arrays of hexagonally packed monomeric RC-LH1-PufX complexes. Transfer of the crtB gene encoding phytoene synthase to TC70 and R-26 restores the normal synthesis of carotenoids demonstrating that the R-26 mutant of Rba. sphaeroides harbours a mutation in crtB, among its other defects. The transconjugant TC70 and R-26 strains containing crtB had regained their ability to assemble wild-type levels of dimeric RC-LH1-PufX core complexes and normal energy transfer pathways were restored, demonstrating that carotenoids are essential for the normal assembly and function of both the LH2 and RC-LH1-PufX complexes in this bacterial photosystem.
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Affiliation(s)
- Irene W Ng
- Department of Molecular Biology and Biochemistry, University of Sheffield S10 2TN, UK
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21
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Collins AM, Qian P, Tang Q, Bocian DF, Hunter CN, Blankenship RE. Light-harvesting antenna system from the phototrophic bacterium Roseiflexus castenholzii. Biochemistry 2010; 49:7524-31. [PMID: 20672862 DOI: 10.1021/bi101036t] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Photosynthetic organisms have evolved diverse light-harvesting complexes to harness light of various qualities and intensities. Photosynthetic bacteria can have (bacterio)chlorophyll Q(y) antenna absorption bands ranging from approximately 650 to approximately 1100 nm. This broad range of wavelengths has allowed many organisms to thrive in unique light environments. Roseiflexus castenholzii is a niche-adapted, filamentous anoxygenic phototroph (FAP) that lacks chlorosomes, the dominant antenna found in most green bacteria, and here we describe the purification of a full complement of photosynthetic complexes: the light-harvesting (LH) antenna, reaction center (RC), and core complex (RC-LH). By high-performance liquid chromatography separation of bacteriochlorophyll and bacteriopheophytin pigments extracted from the core complex and the RC, the number of subunits that comprise the antenna was determined to be 15 +/- 1. Resonance Raman spectroscopy of the carbonyl stretching region displayed modes indicating that 3C-acetyl groups of BChl a are all involved in molecular interactions probably similar to those found in LH1 complexes from purple photosynthetic bacteria. Finally, two-dimensional projections of negatively stained core complexes and the LH antenna revealed a closed, slightly elliptical LH ring with an average diameter of 130 +/- 10 A surrounding a single RC that lacks an H-subunit but is associated with a tetraheme c-type cytochrome.
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Affiliation(s)
- Aaron M Collins
- Department of Biology, Washington University in St. Louis, St. Louis, Missouri 63130, USA
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22
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Proteomic analysis of the developing intracytoplasmic membrane in Rhodobacter sphaeroides during adaptation to low light intensity. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2010. [PMID: 20532741 DOI: 10.1007/978-1-4419-1528-3_10] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register]
Abstract
Although the primary photochemical events in the facultative photoheterotrophic purple bacterium Rhodobacter sphaeroides are now well understood, comparatively little is known about how their photosynthetic apparatus is assembled. Here we present a proteomic analysis of the intracytoplasmic membrane (ICM) assembly process during adaptation to lowered light intensity, in which the size of the photosynthetic units is greatly expanded by addition of the light-harvesting 2 (LH2) peripheral antenna complex. When the isolated ICM-derived chromatophore vesicles were subjected to clear native gel electrophoresis (CNE), four pigmented bands appeared; the top and bottom bands contained the reaction center - light-harvesting 1 (RC-LH1) core complex and LH2 peripheral antenna, respectively, while the two bands of intermediate migration contained associations of the LH2 and core complexes. Proteomic analysis revealed a large array of other proteins associated with the CNE gel bands - in particular, several F(1)F(O)-ATP synthase subunits gave unexpectedly high spectral counts, given the inability to detect this coupling factor, as well as the more abundant cytochrome bc (1) complex, by atomic force microscopy. Significant levels of general membrane assembly factors were also found, as well as numerous proteins of unknown function including high counts for RSP6124 that were correlated with LH2 levels. When combined with further AFM and spectroscopic studies, these proteomic approaches are expected to provide a much-improved understanding of the overall assembly process.
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23
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Hsin J, Strümpfer J, Sener M, Qian P, Hunter CN, Schulten K. Energy Transfer Dynamics in an RC-LH1-PufX Tubular Photosynthetic Membrane. NEW JOURNAL OF PHYSICS 2010; 12:085005. [PMID: 21152381 PMCID: PMC2997751 DOI: 10.1088/1367-2630/12/8/085005] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/30/2023]
Abstract
Light absorption and the subsequent transfer of excitation energy are the first two steps of the photosynthetic process, carried out by protein-bound pigments, mainly bacteriochlorophylls (BChls), in photosynthetic bacteria. BChls are anchored in light-harvesting (LH) complexes, such as light-harvesting complex I (LH1), which directly associates with the reaction center (RC), forming the RC-LH1 core complex. In Rhodobacter sphaeroides, RC-LH1 core complexes contain an additional protein, PufX, and assemble into dimeric RC-LH1-PufX core complexes. In the absence of light-harvesting complexes II, the former complexes can aggregate into a helically ordered tubular photosynthetic membrane. We examined the excitation transfer dynamics in a single RC-LH1-PufX core complex dimer using the hierarchical equations of motion for dissipative quantum dynamics that accurately, yet computationally costly, treat the coupling between BChls and their protein environment. A widely employed description, generalized Förster theory, was also used to calculate the transfer rates of the same excitonic system in order to verify the accuracy of this computationally cheap method. Additionally, in light of the structural uncertainties in the Rhodobacter sphaeroides RC-LH1-PufX core complex, geometrical alterations were introduced in the BChl organization. It is shown that the energy transfer dynamics is not affected by the considered changes in the BChl organization, and that generalized Förster theory provides accurate transfer rates. An all-atom model for a tubular photosynthetic membrane is then constructed on the basis of electron microscopy data, and the overall energy transfer properties of this membrane are computed.
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Affiliation(s)
- Jen Hsin
- Department of Physics and Beckman Institute, University of Illinois at Urbana-Champaign, Urbana, USA
| | - Johan Strümpfer
- Center for Biophysics and Computational Biology and Beckman Institute, University of Illinois at Urbana-Champaign, Urbana, USA
| | - Melih Sener
- Department of Physics and Beckman Institute, University of Illinois at Urbana-Champaign, Urbana, USA
| | - Pu Qian
- 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
| | - Klaus Schulten
- Department of Physics and Beckman Institute, University of Illinois at Urbana-Champaign, Urbana, USA
- Center for Biophysics and Computational Biology and Beckman Institute, University of Illinois at Urbana-Champaign, Urbana, USA
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24
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Hsin J, Gumbart J, Trabuco LG, Villa E, Qian P, Hunter CN, Schulten K. Protein-induced membrane curvature investigated through molecular dynamics flexible fitting. Biophys J 2009; 97:321-9. [PMID: 19580770 PMCID: PMC2711417 DOI: 10.1016/j.bpj.2009.04.031] [Citation(s) in RCA: 62] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/08/2009] [Revised: 04/04/2009] [Accepted: 04/07/2009] [Indexed: 10/20/2022] Open
Abstract
In the photosynthetic purple bacterium Rhodobacter (Rba.) sphaeroides, light is absorbed by membrane-bound light-harvesting (LH) proteins LH1 and LH2. LH1 directly surrounds the reaction center (RC) and, together with PufX, forms a dimeric (RC-LH1-PufX)2 protein complex. In LH2-deficient Rba. sphaeroides mutants, RC-LH1-PufX dimers aggregate into tubular vesicles with a radius of approximately 250-550 A, making RC-LH1-PufX one of the few integral membrane proteins known to actively induce membrane curvature. Recently, a three-dimensional electron microscopy density map showed that the Rba. sphaeroides RC-LH1-PufX dimer exhibits a prominent bend at its dimerizing interface. To investigate the curvature properties of this highly bent protein, we employed molecular dynamics simulations to fit an all-atom structural model of the RC-LH1-PufX dimer within the electron microscopy density map. The simulations reveal how the dimer produces a membrane with high local curvature, even though the location of PufX cannot yet be determined uniquely. The resulting membrane curvature agrees well with the size of RC-LH1-PufX tubular vesicles, and demonstrates how the local curvature properties of the RC-LH1-PufX dimer propagate to form the observed long-range organization of the Rba. sphaeroides tubular vesicles.
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Affiliation(s)
- Jen Hsin
- Department of Physics, University of Illinois at Urbana-Champaign, Urbana, Illinois
- Beckman Institute for Advanced Science and Technology, University of Illinois at Urbana-Champaign, Urbana, Illinois
| | - James Gumbart
- Department of Physics, University of Illinois at Urbana-Champaign, Urbana, Illinois
- Beckman Institute for Advanced Science and Technology, University of Illinois at Urbana-Champaign, Urbana, Illinois
| | - Leonardo G. Trabuco
- Beckman Institute for Advanced Science and Technology, University of Illinois at Urbana-Champaign, Urbana, Illinois
- Center for Biophysics and Computational Biology, University of Illinois at Urbana-Champaign, Urbana, Illinois
| | - Elizabeth Villa
- Beckman Institute for Advanced Science and Technology, University of Illinois at Urbana-Champaign, Urbana, Illinois
- Center for Biophysics and Computational Biology, University of Illinois at Urbana-Champaign, Urbana, Illinois
| | - Pu Qian
- Department of Molecular Biology and Biotechnology, University of Sheffield, Sheffield, United Kingdom
| | - C. Neil Hunter
- Department of Molecular Biology and Biotechnology, University of Sheffield, Sheffield, United Kingdom
| | - Klaus Schulten
- Department of Physics, University of Illinois at Urbana-Champaign, Urbana, Illinois
- Beckman Institute for Advanced Science and Technology, University of Illinois at Urbana-Champaign, Urbana, Illinois
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25
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Sturgis JN, Tucker JD, Olsen JD, Hunter CN, Niederman RA. Atomic Force Microscopy Studies of Native Photosynthetic Membranes. Biochemistry 2009; 48:3679-98. [DOI: 10.1021/bi900045x] [Citation(s) in RCA: 73] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- James N. Sturgis
- Laboratoire d’Ingénierie des Systèmes Macromoléculaires, UPR 9027, Aix Marseille Université, 31 Chemin Joseph Aiguier, 13402 Marseilles, France, Department of Molecular Biology and Biotechnology, University of Sheffield, Sheffield S10 2TN, U.K., and Department of Molecular Biology and Biochemistry, Rutgers University, Piscataway, New Jersey 08854-8082
| | - Jaimey D. Tucker
- Laboratoire d’Ingénierie des Systèmes Macromoléculaires, UPR 9027, Aix Marseille Université, 31 Chemin Joseph Aiguier, 13402 Marseilles, France, Department of Molecular Biology and Biotechnology, University of Sheffield, Sheffield S10 2TN, U.K., and Department of Molecular Biology and Biochemistry, Rutgers University, Piscataway, New Jersey 08854-8082
| | - John D. Olsen
- Laboratoire d’Ingénierie des Systèmes Macromoléculaires, UPR 9027, Aix Marseille Université, 31 Chemin Joseph Aiguier, 13402 Marseilles, France, Department of Molecular Biology and Biotechnology, University of Sheffield, Sheffield S10 2TN, U.K., and Department of Molecular Biology and Biochemistry, Rutgers University, Piscataway, New Jersey 08854-8082
| | - C. Neil Hunter
- Laboratoire d’Ingénierie des Systèmes Macromoléculaires, UPR 9027, Aix Marseille Université, 31 Chemin Joseph Aiguier, 13402 Marseilles, France, Department of Molecular Biology and Biotechnology, University of Sheffield, Sheffield S10 2TN, U.K., and Department of Molecular Biology and Biochemistry, Rutgers University, Piscataway, New Jersey 08854-8082
| | - Robert A. Niederman
- Laboratoire d’Ingénierie des Systèmes Macromoléculaires, UPR 9027, Aix Marseille Université, 31 Chemin Joseph Aiguier, 13402 Marseilles, France, Department of Molecular Biology and Biotechnology, University of Sheffield, Sheffield S10 2TN, U.K., and Department of Molecular Biology and Biochemistry, Rutgers University, Piscataway, New Jersey 08854-8082
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Organization and Assembly of Light-Harvesting Complexes in the Purple Bacterial Membrane. ACTA ACUST UNITED AC 2009. [DOI: 10.1007/978-1-4020-8815-5_14] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 04/07/2023]
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Holden-Dye K, Crouch LI, Jones MR. Structure, function and interactions of the PufX protein. BIOCHIMICA ET BIOPHYSICA ACTA-BIOENERGETICS 2008; 1777:613-30. [DOI: 10.1016/j.bbabio.2008.04.015] [Citation(s) in RCA: 43] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/28/2008] [Revised: 04/06/2008] [Accepted: 04/10/2008] [Indexed: 11/26/2022]
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Qian P, Bullough PA, Hunter CN. Three-dimensional reconstruction of a membrane-bending complex: the RC-LH1-PufX core dimer of Rhodobacter sphaeroides. J Biol Chem 2008; 283:14002-11. [PMID: 18326046 DOI: 10.1074/jbc.m800625200] [Citation(s) in RCA: 86] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
A three-dimensional model of the dimeric reaction center-light harvesting I-PufX (RC-LH1-PufX) complex from Rhodobacter sphaeroides, calculated from electron microscope single particle analysis of negatively stained complexes, shows that the two halves of the dimer molecule incline toward each other on the periplasmic side, creating a remarkable V-shaped structure. The distribution of negative stain is consistent with loose packing of the LH1 ring near the 14th LH1 alpha/beta pair, which could facilitate the migration of quinone and quinol molecules across the LH1 boundary. The three-dimensional model encloses a space near the reaction center Q(B) site and the 14th LH1 alpha/beta pair, which is approximately 20 angstroms in diameter, sufficient to sequester a quinone pool. Helical arrays of dimers were used to construct a three-dimensional membrane model, which matches the packing lattice deduced from electron microscope analysis of the tubular dimer-only membranes found in mutants of Rba. sphaeroides lacking the LH2 complex. The intrinsic curvature of the dimer explains the shape and approximately 70-nm diameter of these membrane tubules, and at least partially accounts for the spherical membrane invaginations found in wild-type Rba. sphaeroides. A model of dimer aggregation and membrane curvature in these spherical membrane invaginations is presented.
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Affiliation(s)
- Pu Qian
- Department of Molecular Biology and Biotechnology, University of Sheffield, Sheffield S10 2TN, United Kingdom
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30
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Structure, Function and Formation of Bacterial Intracytoplasmic Membranes. MICROBIOLOGY MONOGRAPHS 2006. [DOI: 10.1007/7171_025] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
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31
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Rätsep M, Hunter CN, Olsen JD, Freiberg A. Band structure and local dynamics of excitons in bacterial light-harvesting complexes revealed by spectrally selective spectroscopy. PHOTOSYNTHESIS RESEARCH 2005; 86:37-48. [PMID: 16172924 DOI: 10.1007/s11120-005-2749-8] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/12/2005] [Accepted: 02/21/2005] [Indexed: 05/04/2023]
Abstract
Hole-burned absorption and line-narrowed fluorescence spectra are studied at 5 K in wild type and mutant LH1 and LH2 antenna preparations from the photosynthetic purple bacterium Rhodobacter sphaeroides. Evidence was found in all samples, even in intact membranes, of the presence of a broad distribution of bacteriochlorophyll species that are unable to communicate energy between each other and to the exciton states of functional antenna complexes. The distribution maximum of these localized species determined by zero phonon hole action spectroscopy is at 783.5 nm in purified LH1 complexes and at 786.8 nm in B850-only mutant LH2 complexes. A well-resolved peak at 807 nm in LH1 complexes is assigned to the exciton band structure of functional core antenna complexes. Similar structure in LH2 complexes overlaps with the distribution of localized species. Off-diagonal (structural) disorder may be responsible for this exciton band structure. Our data also imply that pair-wise inter-chlorophyll couplings determine the resonance fluorescence lineshape of excitonic polarons.
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Affiliation(s)
- Margus Rätsep
- Institute of Physics, University of Tartu, Riia 142, Tartu, 51014, Estonia
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32
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Hunter CN, Tucker JD, Niederman RA. The assembly and organisation of photosynthetic membranes in Rhodobacter sphaeroides. Photochem Photobiol Sci 2005; 4:1023-7. [PMID: 16307117 DOI: 10.1039/b506099k] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Recent AFM data demonstrate that mature photosynthetic membranes of R. sphaeroides are composed of rows of dimeric RC-LH1-PufX complexes with some LH2 complexes 'sandwiched' between these rows of core complexes, and others in discrete LH2-only domains which might form the light-responsive complement of the LH2 antenna. The present work applies membrane fractionation, radiolabelling and LDS-PAGE techniques to investigate the response of R. sphaeroides to lowered light intensity. The kinetics underlying this adaptation to low light conditions were revealed by radiolabelling with the bacteriochlorophyll (bchl) biosynthetic precursor, delta-aminolevulinate, which allowed us to measure only the bchls synthesised after the light intensity shift. We show that (1) the increase in LH2 antenna size is mainly restricted to the mature ICM membrane fraction, and the antenna composition of the precursor upper pigmented band (UPB) membrane remains constant, (2) the precursor UPB membrane is enriched in bchl synthase, the terminal enzyme of the bchl biosynthetic pathway, and (3) the LH2 and the complexes of intermediate migration in LDS-PAGE exhibit completely different labelling kinetics. Thus, new photosynthetic complexes, mainly LH2, are synthesised and assembled at the membrane initiation UPB sites, where the LH2 rings pack between the rows of dimeric cores fostering new LH2-LH1 interactions. Mature membranes also assemble new LH2 rings, but in this case the 'sandwich' regions between the rows of core dimers are already fully occupied and the bulk antenna pool is the favoured location for these new LH2 complexes.
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Affiliation(s)
- C Neil Hunter
- Department of Molecular Biology and Biotechnology, University of Sheffield, Sheffield, UK S10 2TN
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33
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Bahatyrova S, Frese RN, van der Werf KO, Otto C, Hunter CN, Olsen JD. Flexibility and size heterogeneity of the LH1 light harvesting complex revealed by atomic force microscopy: functional significance for bacterial photosynthesis. J Biol Chem 2004; 279:21327-33. [PMID: 14993213 DOI: 10.1074/jbc.m313039200] [Citation(s) in RCA: 92] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Previous electron microscopic studies of bacterial RCLH1 complexes demonstrated both circular and elliptical conformations of the LH1 ring, and this implied flexibility has been suggested to allow passage of quinol from the Q(B) site of the RC to the quinone pool prior to reduction of the cytochrome bc(1) complex. We have used atomic force microscopy to demonstrate that these are just two of many conformations for the LH1 ring, which displays large molecule-to-molecule variations, in terms of both shape and size. This atomic force microscope study has used a mutant lacking the reaction center complex, which normally sits within the LH1 ring providing a barrier to substantial changes in shape. This approach has revealed the inherent flexibility and lack of structural coherence of this complex in a reconstituted lipid bilayer at room temperature. Circular, elliptical, and even polygonal ring shapes as well as arcs and open rings have been observed for LH1; in contrast, no such variations in structure were observed for the LH2 complex under the same conditions. The basis for these differences between LH1 and LH2 is suggested to be the H-bonding patterns that stabilize binding of the bacteriochlorophylls to the LH polypeptides. The existence of open rings and arcs provides a direct visualization of the consequences of the relatively weak associations that govern the aggregation of the protomers (alpha(1)beta(1)Bchl(2)) comprising the LH1 complex. The demonstration that the linkage between adjacent protomer units is flexible and can even be uncoupled at room temperature in a detergent-free membrane bilayer provides a rationale for the dynamic separation of individual protomers, and we may now envisage experiments that seek to prove this active opening process.
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Affiliation(s)
- Svetlana Bahatyrova
- Biophysical Techniques Group, Department of Science and Technology, University of Twente, 7500 AE Enschede, The Netherlands
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34
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Siebert CA, Qian P, Fotiadis D, Engel A, Hunter CN, Bullough PA. Molecular architecture of photosynthetic membranes in Rhodobacter sphaeroides: the role of PufX. EMBO J 2004; 23:690-700. [PMID: 14765115 PMCID: PMC381000 DOI: 10.1038/sj.emboj.7600092] [Citation(s) in RCA: 142] [Impact Index Per Article: 7.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/27/2003] [Accepted: 01/05/2004] [Indexed: 01/08/2023] Open
Abstract
The effects of the PufX polypeptide on membrane architecture were investigated by comparing the composition and structures of photosynthetic membranes from PufX+ and PufX- strains of Rhodobacter sphaeroides. We show that this single polypeptide profoundly affects membrane morphology, leading to highly elongated cells containing extended tubular membranes. Purified tubular membranes contain helical arrays composed solely of dimeric RC-LH1-PufX (RC, reaction centre; LH, light harvesting) complexes with apparently open LH1 rings. PufX- cells contain crystalline membranes with a pseudo-hexagonal packing of monomeric core complexes. Analysis of purified complexes by electron microscopy and atomic force microscopy shows that LH1 and PufX form a continuous ring of protein around each RC. A model of the tubular membrane is presented with PufX located adjacent to the stained region created by a vacant LH1beta. This arrangement, coupled with a flexible ring, would give the RC QB site transient access to the interstices in the lattice, which might be of functional importance. We discuss the implications of our data for the export of quinol from the RC, for eventual reduction of the cytochrome bc1 complex.
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Affiliation(s)
- C Alistair Siebert
- Department of Molecular Biology and Biotechnology, University of Sheffield, Krebs Institute for Biomolecular Research, Sheffield, UK
| | - Pu Qian
- Department of Molecular Biology and Biotechnology, University of Sheffield, Krebs Institute for Biomolecular Research, Sheffield, UK
| | - Dimitrios Fotiadis
- University of Basel, Biozentrum, ME Müller Institute for Structural Biology, Basel, Switzerland
| | - Andreas Engel
- University of Basel, Biozentrum, ME Müller Institute for Structural Biology, Basel, Switzerland
| | - C Neil Hunter
- Department of Molecular Biology and Biotechnology, University of Sheffield, Krebs Institute for Biomolecular Research, Sheffield, UK
| | - Per A Bullough
- Department of Molecular Biology and Biotechnology, University of Sheffield, Krebs Institute for Biomolecular Research, Sheffield, UK
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Scheuring S, Francia F, Busselez J, Melandri BA, Rigaud JL, Lévy D. Structural Role of PufX in the Dimerization of the Photosynthetic Core Complex of Rhodobacter sphaeroides. J Biol Chem 2004; 279:3620-6. [PMID: 14581468 DOI: 10.1074/jbc.m310050200] [Citation(s) in RCA: 113] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Monomeric and dimeric PufX-containing core complexes have been purified from membranes of wild-type Rhodobacter sphaeroides. Reconstitution of both samples by detergent removal in the presence of lipids leads to the formation of two-dimensional crystals constituted of dimeric core complexes. Two-dimensional crystals were further analyzed by cryoelectron microscopy and atomic force microscopy. A projection map at 26-A resolution reveals that core complexes assemble in an "S"-shaped dimeric complex. Each core complex is composed of one reaction center, 12 light-harvesting 1 alpha/beta-heterodimers, and one PufX protein. The light-harvesting 1 assemblies are open with a gap of density of approximately 30-A width and surround oriented reaction centers. A maximum density is found at the dimer junction. Based on the projection map, a model is proposed, in which the two PufX proteins are located at the dimer junction, consistent with the finding of dimerization of monomeric core complexes upon reconstitution. This localization of PufX in the core complex implies that PufX is the structural key for the dimer complex formation rather than a channel-forming protein for the exchange of ubiquinone/ubiquinol between the reaction center and the cytochrome bc1 complex.
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Affiliation(s)
- Simon Scheuring
- Institut Curie, UMR-CNRS 168 and LRC-CEA 34V, 11 Rue Pierre et Marie Curie, 75231 Paris Cedex 05, France
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36
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Qian P, Addlesee HA, Ruban AV, Wang P, Bullough PA, Hunter CN. A reaction center-light-harvesting 1 complex (RC-LH1) from a Rhodospirillum rubrum mutant with altered esterifying pigments: characterization by optical spectroscopy and cryo-electron microscopy. J Biol Chem 2003; 278:23678-85. [PMID: 12719425 DOI: 10.1074/jbc.m302753200] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Introduction of the bchP gene from Rhodobacter sphaeroides encoding geranylgeranyl reductase into Rhodospirillum rubrum alters the esterification of the bacteriochlorophylls so that phytol is used instead of geranylgeraniol. The resulting transconjugant strain of Rs. rubrum grows photosynthetically, showing that phytolated Bchla can substitute for the native pigment in both the reaction center (RC) and the light-harvesting 1 (LH1) complexes. This genetic manipulation perturbs the native carotenoid biosynthetic pathway; several biosynthetic intermediates are assembled into the core complex and are capable of energy transfer to the bacteriochlorophylls. RC-LH1 complexes containing phytolated Bchla were analyzed by low temperature absorption and fluorescence spectroscopy and circular dichroism. These show that phytolated Bchls can assemble in vivo into the photosynthetic apparatus of Rs. rubrum and that the newly introduced phytol tail provokes small perturbations to the Bchls within their binding sites in the LH1 complex. The RC-LH1 core complex was purified from membranes and reconstituted into well ordered two-dimensional crystals with a p4212 space group. A projection map calculated to 9 A shows clearly that the LH1 ring from the mutant is composed of 16 subunits that surround the reaction center and that the diameter of this complex is in close agreement with that of the wild-type LH1 complex.
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Affiliation(s)
- Pu Qian
- Department of Molecular Biology and Biotechnology, University of Sheffield, Firth Court, Western Bank, Sheffield S10 2TN, United Kingdom
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37
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Végh AP, Robert B. Spectroscopic characterisation of a tetrameric subunit form of the core antenna protein from Rhodospirillum rubrum. FEBS Lett 2002; 528:222-6. [PMID: 12297309 DOI: 10.1016/s0014-5793(02)03314-8] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
Abstract
The core light-harvesting complex (LH1) of Rhodospirillum rubrum is constituted of multiple heterodimeric subunits, each containing two transmembrane polypeptides, alpha and beta. The detergent octylglucoside induces the stepwise dissociation of LH1 into B820 (an alphabeta dimer) and B777 (monomeric polypeptides), both of which still retain their bound bacteriochlorophyll molecules. We have investigated the absorption properties of B820 as a function of temperature, whereby a spectral population called 'B851' has been characterised. We show evidence that it is a dimer of the B820 complex. This may represent an intermediate oligomeric form in the process of the LH1 ring formation, as its existence was predicted from global analysis of the absorption spectra of the LH1/B820 equilibrium [Pandit et al. (2001) Biochemistry 40, 12913-12924]. Stabilisation of this dissociated form of LH1 may help in understanding both the electronic properties and the association process of these integral membrane proteins.
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Affiliation(s)
- Attila P Végh
- Section de Biophysique des Fonctions Membranaires, DBJC/CEA et URA CNRS 2096 C.E.A Saclay, 91191 Gif/Yvette Cedex, France.
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