1
|
Huang X, Vasilev C, Swainsbury D, Hunter C. Excitation energy transfer in proteoliposomes reconstituted with LH2 and RC-LH1 complexes from Rhodobacter sphaeroides. Biosci Rep 2024; 44:BSR20231302. [PMID: 38227291 PMCID: PMC10876425 DOI: 10.1042/bsr20231302] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/03/2023] [Revised: 12/30/2023] [Accepted: 01/16/2024] [Indexed: 01/17/2024] Open
Abstract
Light-harvesting 2 (LH2) and reaction-centre light-harvesting 1 (RC-LH1) complexes purified from the photosynthetic bacterium Rhodobacter (Rba.) sphaeroides were reconstituted into proteoliposomes either separately, or together at three different LH2:RC-LH1 ratios, for excitation energy transfer studies. Atomic force microscopy (AFM) was used to investigate the distribution and association of the complexes within the proteoliposome membranes. Absorption and fluorescence emission spectra were similar for LH2 complexes in detergent and liposomes, indicating that reconstitution retains the structural and optical properties of the LH2 complexes. Analysis of fluorescence emission shows that when LH2 forms an extensive series of contacts with other such complexes, fluorescence is quenched by 52.6 ± 1.4%. In mixed proteoliposomes, specific excitation of carotenoids in LH2 donor complexes resulted in emission of fluorescence from acceptor RC-LH1 complexes engineered to assemble with no carotenoids. Extents of energy transfer were measured by fluorescence lifetime microscopy; the 0.72 ± 0.08 ns lifetime in LH2-only membranes decreases to 0.43 ± 0.04 ns with a ratio of 2:1 LH2 to RC-LH1, and to 0.35 ± 0.05 ns for a 1:1 ratio, corresponding to energy transfer efficiencies of 40 ± 14% and 51 ± 18%, respectively. No further improvement is seen with a 0.5:1 LH2 to RC-LH1 ratio. Thus, LH2 and RC-LH1 complexes perform their light harvesting and energy transfer roles when reconstituted into proteoliposomes, providing a way to integrate native, non-native, engineered and de novo designed light-harvesting complexes into functional photosynthetic systems.
Collapse
Affiliation(s)
- Xia Huang
- Department of Biological Sciences, Xi’an Jiaotong-Liverpool University, Suzhou, Jiangsu 215123, China
- Jinan Guoke Medical Technology Development Co., Ltd, Jinan, Shandong 250101, China
- School of Biosciences, University of Sheffield, Sheffield S10 2TN, U.K
| | - Cvetelin Vasilev
- School of Biosciences, University of Sheffield, Sheffield S10 2TN, U.K
| | - David J.K. Swainsbury
- School of Biosciences, University of Sheffield, Sheffield S10 2TN, U.K
- School of Biological Sciences, University of East Anglia, Norwich, NR4 7TJ, U.K
| | - C. Neil Hunter
- School of Biosciences, University of Sheffield, Sheffield S10 2TN, U.K
| |
Collapse
|
2
|
Structural basis for the assembly and quinone transport mechanisms of the dimeric photosynthetic RC-LH1 supercomplex. Nat Commun 2022; 13:1977. [PMID: 35418573 PMCID: PMC9007983 DOI: 10.1038/s41467-022-29563-3] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/28/2021] [Accepted: 03/22/2022] [Indexed: 12/15/2022] Open
Abstract
The reaction center (RC) and light-harvesting complex 1 (LH1) form a RC-LH1 core supercomplex that is vital for the primary reactions of photosynthesis in purple phototrophic bacteria. Some species possess the dimeric RC-LH1 complex with a transmembrane polypeptide PufX, representing the largest photosynthetic complex in anoxygenic phototrophs. However, the details of the architecture and assembly mechanism of the RC-LH1 dimer are unclear. Here we report seven cryo-electron microscopy (cryo-EM) structures of RC-LH1 supercomplexes from Rhodobacter sphaeroides. Our structures reveal that two PufX polypeptides are positioned in the center of the S-shaped RC-LH1 dimer, interlocking association between the components and mediating RC-LH1 dimerization. Moreover, we identify another transmembrane peptide, designated PufY, which is located between the RC and LH1 subunits near the LH1 opening. PufY binds a quinone molecule and prevents LH1 subunits from completely encircling the RC, creating a channel for quinone/quinol exchange. Genetic mutagenesis, cryo-EM structures, and computational simulations provide a mechanistic understanding of the assembly and electron transport pathways of the RC-LH1 dimer and elucidate the roles of individual components in ensuring the structural and functional integrity of the photosynthetic supercomplex.
Collapse
|
3
|
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: 12] [Impact Index Per Article: 4.0] [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.
Collapse
|
4
|
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: 14] [Impact Index Per Article: 4.7] [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.
Collapse
|
5
|
Cryo-EM structure of the Rhodospirillum rubrum RC-LH1 complex at 2.5 Å. Biochem J 2021; 478:3253-3263. [PMID: 34402504 PMCID: PMC8454704 DOI: 10.1042/bcj20210511] [Citation(s) in RCA: 10] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/06/2021] [Revised: 08/12/2021] [Accepted: 08/17/2021] [Indexed: 12/03/2022]
Abstract
The reaction centre light-harvesting 1 (RC–LH1) complex is the core functional component of bacterial photosynthesis. We determined the cryo-electron microscopy (cryo-EM) structure of the RC–LH1 complex from Rhodospirillum rubrum at 2.5 Å resolution, which reveals a unique monomeric bacteriochlorophyll with a phospholipid ligand in the gap between the RC and LH1 complexes. The LH1 complex comprises a circular array of 16 αβ-polypeptide subunits that completely surrounds the RC, with a preferential binding site for a quinone, designated QP, on the inner face of the encircling LH1 complex. Quinols, initially generated at the RC QB site, are proposed to transiently occupy the QP site prior to traversing the LH1 barrier and diffusing to the cytochrome bc1 complex. Thus, the QP site, which is analogous to other such sites in recent cryo-EM structures of RC–LH1 complexes, likely reflects a general mechanism for exporting quinols from the RC–LH1 complex.
Collapse
|
6
|
Onizhuk M, Sohoni S, Galli G, Engel GS. Spatial Patterns of Light-Harvesting Antenna Complex Arrangements Tune the Transfer-to-Trap Efficiency of Excitons in Purple Bacteria. J Phys Chem Lett 2021; 12:6967-6973. [PMID: 34283617 DOI: 10.1021/acs.jpclett.1c01537] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/13/2023]
Abstract
In photosynthesis, the efficiency with which a photogenerated exciton reaches the reaction center is dictated by chromophore energies and the arrangement of chromophores in the supercomplex. Here, we explore the interplay between the arrangement of light-harvesting antennae and the efficiency of exciton transport in purple bacterial photosynthesis. Using a Miller-Abrahams-based exciton hopping model, we compare different arrangements of light-harvesting proteins on the intracytoplasmic membrane. We find that arrangements with aggregated LH1s have a higher efficiency than arrangements with randomly distributed LH1s in a wide range of physiological light fluences. This effect is robust to the introduction of defects on the intracytoplasmic membrane. Our result explains the absence of species with aggregated LH1 arrangements in low-light niches and the large increase seen in the expression of LH1 dimer complexes in high fluences. We suggest that the effect seen in our study is an adaptive strategy toward solar light fluence across different purple bacterial species.
Collapse
Affiliation(s)
- Mykyta Onizhuk
- Department of Chemistry, The University of Chicago, Chicago, Illinois 60637, United States
| | - Siddhartha Sohoni
- Department of Chemistry, The University of Chicago, Chicago, Illinois 60637, United States
- James Franck Institute, The University of Chicago, Chicago, Illinois 60637, United States
- The Institute for Biophysical Dynamics, The University of Chicago, Chicago, Illinois 60637, United States
| | - Giulia Galli
- Department of Chemistry, The University of Chicago, Chicago, Illinois 60637, United States
- Pritzker School of Molecular Engineering, The University of Chicago, Chicago, Illinois 60637, United States
- Materials Science Division and Center for Molecular Engineering, Argonne National Laboratory, Lemont, Illinois 60439, United States
| | - Gregory S Engel
- Department of Chemistry, The University of Chicago, Chicago, Illinois 60637, United States
- James Franck Institute, The University of Chicago, Chicago, Illinois 60637, United States
- The Institute for Biophysical Dynamics, The University of Chicago, Chicago, Illinois 60637, United States
| |
Collapse
|
7
|
Uragami C, Sato H, Yukihira N, Fujiwara M, Kosumi D, Gardiner AT, Cogdell RJ, Hashimoto H. Photoprotective mechanisms in the core LH1 antenna pigment-protein complex from the purple photosynthetic bacterium, Rhodospirillum rubrum. J Photochem Photobiol A Chem 2020. [DOI: 10.1016/j.jphotochem.2020.112628] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022]
|
8
|
Eisenhardt KMH, Reuscher CM, Klug G. PcrX, an sRNA derived from the 3'- UTR of the Rhodobacter sphaeroides puf operon modulates expression of puf genes encoding proteins of the bacterial photosynthetic apparatus. Mol Microbiol 2018; 110:325-334. [PMID: 29995316 DOI: 10.1111/mmi.14076] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 07/03/2018] [Indexed: 11/30/2022]
Abstract
Facultative phototrophic bacteria like Rhodobacter sphaeroides can produce ATP by anoxygenic photosynthesis, which is of advantage under conditions with limiting oxygen. However, the simultaneous presence of pigments, light and oxygen leads to the generation of harmful singlet oxygen. In order to avoid this stress situation, the formation of photosynthetic complexes is tightly regulated by light and oxygen signals. In a complex regulatory network several regulatory proteins and the small non-coding RNA PcrZ contribute to the balanced expression of photosynthesis genes. With PcrX this study identifies a second sRNA that is part of this network. The puf operon encodes pigment binding proteins of the light-harvesting I complex (PufBA) and of the reaction center (PufLM), a protein regulating porphyrin flux (PufQ), and a scaffolding protein (PufX). The PcrX sRNA is derived from the 3' UTR of the puf operon mRNA by RNase E-mediated cleavage. It targets the pufX mRNA segment, reduces the half-life of the pufBALMX mRNA and as a consequence affects the level of photosynthetic complexes. By its action PcrX counteracts the increased expression of photosynthesis genes that is mediated by protein regulators and is thus involved in balancing the formation of photosynthetic complexes in response to external stimuli.
Collapse
Affiliation(s)
- Katrin M H Eisenhardt
- Institut für Mikrobiologie und Molekularbiologie, Justus Liebig Universität Giessen, IFZ, Giessen, Germany
| | - Carina M Reuscher
- Institut für Mikrobiologie und Molekularbiologie, Justus Liebig Universität Giessen, IFZ, Giessen, Germany
| | - Gabriele Klug
- Institut für Mikrobiologie und Molekularbiologie, Justus Liebig Universität Giessen, IFZ, Giessen, Germany
| |
Collapse
|
9
|
Jackson PJ, Hitchcock A, Swainsbury DJK, Qian P, Martin EC, Farmer DA, Dickman MJ, Canniffe DP, Hunter CN. Identification of protein W, the elusive sixth subunit of the Rhodopseudomonas palustris reaction center-light harvesting 1 core complex. BIOCHIMICA ET BIOPHYSICA ACTA-BIOENERGETICS 2017; 1859:119-128. [PMID: 29126780 PMCID: PMC5764122 DOI: 10.1016/j.bbabio.2017.11.001] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 07/25/2017] [Revised: 11/03/2017] [Accepted: 11/06/2017] [Indexed: 02/08/2023]
Abstract
The X-ray crystal structure of the Rhodopseudomonas (Rps.) palustris reaction center-light harvesting 1 (RC-LH1) core complex revealed the presence of a sixth protein component, variably referred to in the literature as helix W, subunit W or protein W. The position of this protein prevents closure of the LH1 ring, possibly to allow diffusion of ubiquinone/ubiquinol between the RC and the cytochrome bc1 complex in analogous fashion to the well-studied PufX protein from Rhodobacter sphaeroides. The identity and function of helix W have remained unknown for over 13 years; here we use a combination of biochemistry, mass spectrometry, molecular genetics and electron microscopy to identify this protein as RPA4402 in Rps. palustris CGA009. Protein W shares key conserved sequence features with PufX homologs, and although a deletion mutant was able to grow under photosynthetic conditions with no discernible phenotype, we show that a tagged version of protein W pulls down the RC-LH1 complex. Protein W is not encoded in the photosynthesis gene cluster and our data indicate that only approximately 10% of wild-type Rps. palustris core complexes contain this non-essential subunit; functional and evolutionary consequences of this observation are discussed. The ability to purify uniform RC-LH1 and RC-LH1-protein W preparations will also be beneficial for future structural studies of these bacterial core complexes. Identification of the protein W subunit of the Rps. palustris RC-LH1 core complex. The rpa4402 locus encoding protein W is not in the PGC. Protein W is present in only a sub-population of core complexes. Protein W is dispensable for photosynthetic growth. Pure plus/minus protein W core complex preparations will aid structural studies.
Collapse
Affiliation(s)
- Philip J Jackson
- Department of Molecular Biology and Biotechnology, University of Sheffield, Sheffield, UK; ChELSI Institute, Department of Chemical and Biological Engineering, University of Sheffield, Sheffield, UK
| | - Andrew Hitchcock
- Department of Molecular Biology and Biotechnology, University of Sheffield, Sheffield, UK
| | - David J K Swainsbury
- Department of Molecular Biology and Biotechnology, University of Sheffield, Sheffield, UK
| | - Pu Qian
- Department of Molecular Biology and Biotechnology, University of Sheffield, Sheffield, UK
| | - Elizabeth C Martin
- Department of Molecular Biology and Biotechnology, University of Sheffield, Sheffield, UK
| | - David A Farmer
- Department of Molecular Biology and Biotechnology, University of Sheffield, Sheffield, UK
| | - Mark J Dickman
- ChELSI Institute, Department of Chemical and Biological Engineering, University of Sheffield, Sheffield, UK
| | - Daniel P Canniffe
- Department of Molecular Biology and Biotechnology, University of Sheffield, Sheffield, UK
| | - C Neil Hunter
- Department of Molecular Biology and Biotechnology, University of Sheffield, Sheffield, UK.
| |
Collapse
|
10
|
Mapping the ultrafast flow of harvested solar energy in living photosynthetic cells. Nat Commun 2017; 8:988. [PMID: 29042567 PMCID: PMC5715167 DOI: 10.1038/s41467-017-01124-z] [Citation(s) in RCA: 33] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/03/2016] [Accepted: 08/20/2017] [Indexed: 11/23/2022] Open
Abstract
Photosynthesis transfers energy efficiently through a series of antenna complexes to the reaction center where charge separation occurs. Energy transfer in vivo is primarily monitored by measuring fluorescence signals from the small fraction of excitations that fail to result in charge separation. Here, we use two-dimensional electronic spectroscopy to follow the entire energy transfer process in a thriving culture of the purple bacteria, Rhodobacter sphaeroides. By removing contributions from scattered light, we extract the dynamics of energy transfer through the dense network of antenna complexes and into the reaction center. Simulations demonstrate that these dynamics constrain the membrane organization into small pools of core antenna complexes that rapidly trap energy absorbed by surrounding peripheral antenna complexes. The rapid trapping and limited back transfer of these excitations lead to transfer efficiencies of 83% and a small functional light-harvesting unit. During photosynthesis, energy is transferred from photosynthetic antenna to reaction centers via ultrafast energy transfer. Here the authors track energy transfer in photosynthetic bacteria using two-dimensional electronic spectroscopy and show that these transfer dynamics constrain antenna complex organization.
Collapse
|
11
|
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.
Collapse
|
12
|
Olsen JD, Martin EC, Hunter CN. The PufX quinone channel enables the light-harvesting 1 antenna to bind more carotenoids for light collection and photoprotection. FEBS Lett 2017; 591:573-580. [PMID: 28130884 PMCID: PMC5347945 DOI: 10.1002/1873-3468.12575] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/24/2016] [Revised: 01/12/2017] [Accepted: 01/16/2017] [Indexed: 11/30/2022]
Abstract
Photosynthesis in some phototrophic bacteria requires the PufX component of the reaction centre–light‐harvesting 1–PufX (RC‐LH1‐PufX) complex, which creates a pore for quinone/quinol (Q/QH2) exchange across the LH1 barrier surrounding the RC. However, photosynthetic bacteria such as Thermochromatium (T.) tepidum do not require PufX because there are fewer carotenoid binding sites, which creates multiple pores in the LH1 ring for Q/QH2 exchange. We show that an αTrp‐24→Phe alteration of the Rhodobacter (Rba.) sphaeroides LH1 antenna impairs carotenoid binding and allows photosynthetic growth in the absence of PufX. We propose that acquisition of PufX and confining Q/QH2 traffic to a pore adjacent to the RC QB site is an evolutionary upgrade that allows increased LH1 carotenoid content for enhanced light absorption and photoprotection.
Collapse
Affiliation(s)
- John D Olsen
- Department of Molecular Biology and Biotechnology, University of Sheffield, UK
| | - Elizabeth C Martin
- Department of Molecular Biology and Biotechnology, University of Sheffield, UK
| | - C Neil Hunter
- Department of Molecular Biology and Biotechnology, University of Sheffield, UK
| |
Collapse
|
13
|
Dahlberg PD, Ting PC, Massey SC, Martin EC, Hunter CN, Engel GS. Electronic Structure and Dynamics of Higher-Lying Excited States in Light Harvesting Complex 1 from Rhodobacter sphaeroides. J Phys Chem A 2016; 120:4124-30. [PMID: 27232937 PMCID: PMC5668141 DOI: 10.1021/acs.jpca.6b04146] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Light harvesting in photosynthetic organisms involves efficient transfer of energy from peripheral antenna complexes to core antenna complexes, and ultimately to the reaction center where charge separation drives downstream photosynthetic processes. Antenna complexes contain many strongly coupled chromophores, which complicates analysis of their electronic structure. Two-dimensional electronic spectroscopy (2DES) provides information on energetic coupling and ultrafast energy transfer dynamics, making the technique well suited for the study of photosynthetic antennae. Here, we present 2DES results on excited state properties and dynamics of a core antenna complex, light harvesting complex 1 (LH1), embedded in the photosynthetic membrane of Rhodobacter sphaeroides. The experiment reveals weakly allowed higher-lying excited states in LH1 at 770 nm, which transfer energy to the strongly allowed states at 875 nm with a lifetime of 40 fs. The presence of higher-lying excited states is in agreement with effective Hamiltonians constructed using parameters from crystal structures and atomic force microscopy (AFM) studies. The energy transfer dynamics between the higher- and lower-lying excited states agree with Redfield theory calculations.
Collapse
Affiliation(s)
- Peter D. Dahlberg
- Graduate Program in the Biophysical Sciences, Institute for Biophysical Dynamics, and the James Franck Institute, The University of Chicago, Chicago, IL 60637
| | - Po-Chieh Ting
- Department of Chemistry, Institute for Biophysical Dynamics, and the James Franck Institute, The University of Chicago, Chicago, IL 60637
| | - Sara C. Massey
- Department of Chemistry, Institute for Biophysical Dynamics, and the James Franck Institute, The University of Chicago, Chicago, IL 60637
| | - Elizabeth C. Martin
- Department of Molecular Biology and Biotechnology, University of Sheffield, Firth Court, Western Bank, Sheffield S10 2TN, UK
| | - C. Neil Hunter
- Department of Molecular Biology and Biotechnology, University of Sheffield, Firth Court, Western Bank, Sheffield S10 2TN, UK
| | - Gregory S. Engel
- Department of Chemistry, Institute for Biophysical Dynamics, and the James Franck Institute, The University of Chicago, Chicago, IL 60637
| |
Collapse
|
14
|
Uragami C, Sugai Y, Hanjo K, Sumino A, Fujii R, Nishioka T, Kinoshita I, Dewa T, Nango M, Gardiner AT, Cogdell RJ, Hashimoto H. Observation of hybrid artificial photosynthetic membranes using peripheral and core antennae from two different species of photosynthetic bacteria by AFM and fluorescence micro-spectroscopy. J Photochem Photobiol A Chem 2015. [DOI: 10.1016/j.jphotochem.2015.06.009] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
|
15
|
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.
Collapse
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.
| |
Collapse
|
16
|
Mothersole DJ, Jackson PJ, Vasilev C, Tucker JD, Brindley AA, Dickman MJ, Hunter CN. PucC and LhaA direct efficient assembly of the light-harvesting complexes in Rhodobacter sphaeroides. Mol Microbiol 2015; 99:307-27. [PMID: 26419219 PMCID: PMC4949548 DOI: 10.1111/mmi.13235] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 09/28/2015] [Indexed: 01/21/2023]
Abstract
The mature architecture of the photosynthetic membrane of the purple phototroph Rhodobacter sphaeroides has been characterised to a level where an atomic-level membrane model is available, but the roles of the putative assembly proteins LhaA and PucC in establishing this architecture are unknown. Here we investigate the assembly of light-harvesting LH2 and reaction centre-light-harvesting1-PufX (RC-LH1-PufX) photosystem complexes using spectroscopy, pull-downs, native gel electrophoresis, quantitative mass spectrometry and fluorescence lifetime microscopy to characterise a series of lhaA and pucC mutants. LhaA and PucC are important for specific assembly of LH1 or LH2 complexes, respectively, but they are not essential; the few LH1 subunits found in ΔlhaA mutants assemble to form normal RC-LH1-PufX core complexes showing that, once initiated, LH1 assembly round the RC is cooperative and proceeds to completion. LhaA and PucC form oligomers at sites of initiation of membrane invagination; LhaA associates with RCs, bacteriochlorophyll synthase (BchG), the protein translocase subunit YajC and the YidC membrane protein insertase. These associations within membrane nanodomains likely maximise interactions between pigments newly arriving from BchG and nascent proteins within the SecYEG-SecDF-YajC-YidC assembly machinery, thereby co-ordinating pigment delivery, the co-translational insertion of LH polypeptides and their folding and assembly to form photosynthetic complexes.
Collapse
Affiliation(s)
- David J Mothersole
- Department of Molecular Biology and Biotechnology, University of Sheffield, Firth Court, Western Bank, Sheffield, S10 2TN, UK
| | - Philip J Jackson
- Department of Molecular Biology and Biotechnology, University of Sheffield, Firth Court, Western Bank, Sheffield, S10 2TN, UK.,ChELSI Institute, Department of Chemical and Biological Engineering, University of Sheffield, Mappin Street, Sheffield, S1 3JD, UK
| | - Cvetelin Vasilev
- Department of Molecular Biology and Biotechnology, University of Sheffield, Firth Court, Western Bank, Sheffield, S10 2TN, UK
| | - Jaimey D Tucker
- Department of Molecular Biology and Biotechnology, University of Sheffield, Firth Court, Western Bank, Sheffield, S10 2TN, UK
| | - Amanda A Brindley
- Department of Molecular Biology and Biotechnology, University of Sheffield, Firth Court, Western Bank, Sheffield, S10 2TN, UK
| | - Mark J Dickman
- ChELSI Institute, Department of Chemical and Biological Engineering, University of Sheffield, Mappin Street, Sheffield, S1 3JD, UK
| | - C Neil Hunter
- Department of Molecular Biology and Biotechnology, University of Sheffield, Firth Court, Western Bank, Sheffield, S10 2TN, UK
| |
Collapse
|
17
|
Effects of the protonophore carbonyl-cyanide m-chlorophenylhydrazone on intracytoplasmic membrane assembly in Rhodobacter sphaeroides. BIOCHIMICA ET BIOPHYSICA ACTA-BIOENERGETICS 2015; 1847:1119-28. [DOI: 10.1016/j.bbabio.2015.06.002] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/17/2015] [Revised: 06/02/2015] [Accepted: 06/03/2015] [Indexed: 11/20/2022]
|