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Photosynthesis tunes quantum-mechanical mixing of electronic and vibrational states to steer exciton energy transfer. Proc Natl Acad Sci U S A 2021; 118:2018240118. [PMID: 33688046 DOI: 10.1073/pnas.2018240118] [Citation(s) in RCA: 23] [Impact Index Per Article: 7.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022] Open
Abstract
Photosynthetic species evolved to protect their light-harvesting apparatus from photoxidative damage driven by intracellular redox conditions or environmental conditions. The Fenna-Matthews-Olson (FMO) pigment-protein complex from green sulfur bacteria exhibits redox-dependent quenching behavior partially due to two internal cysteine residues. Here, we show evidence that a photosynthetic complex exploits the quantum mechanics of vibronic mixing to activate an oxidative photoprotective mechanism. We use two-dimensional electronic spectroscopy (2DES) to capture energy transfer dynamics in wild-type and cysteine-deficient FMO mutant proteins under both reducing and oxidizing conditions. Under reducing conditions, we find equal energy transfer through the exciton 4-1 and 4-2-1 pathways because the exciton 4-1 energy gap is vibronically coupled with a bacteriochlorophyll-a vibrational mode. Under oxidizing conditions, however, the resonance of the exciton 4-1 energy gap is detuned from the vibrational mode, causing excitons to preferentially steer through the indirect 4-2-1 pathway to increase the likelihood of exciton quenching. We use a Redfield model to show that the complex achieves this effect by tuning the site III energy via the redox state of its internal cysteine residues. This result shows how pigment-protein complexes exploit the quantum mechanics of vibronic coupling to steer energy transfer.
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Greening C, Lithgow T. Formation and function of bacterial organelles. Nat Rev Microbiol 2020; 18:677-689. [PMID: 32710089 DOI: 10.1038/s41579-020-0413-0] [Citation(s) in RCA: 70] [Impact Index Per Article: 17.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 06/22/2020] [Indexed: 01/28/2023]
Abstract
Advances in imaging technologies have revealed that many bacteria possess organelles with a proteomically defined lumen and a macromolecular boundary. Some are bound by a lipid bilayer (such as thylakoids, magnetosomes and anammoxosomes), whereas others are defined by a lipid monolayer (such as lipid bodies), a proteinaceous coat (such as carboxysomes) or have a phase-defined boundary (such as nucleolus-like compartments). These diverse organelles have various metabolic and physiological functions, facilitating adaptation to different environments and driving the evolution of cellular complexity. This Review highlights that, despite the diversity of reported organelles, some unifying concepts underlie their formation, structure and function. Bacteria have fundamental mechanisms of organelle formation, through which conserved processes can form distinct organelles in different species depending on the proteins recruited to the luminal space and the boundary of the organelle. These complex subcellular compartments provide evolutionary advantages as well as enabling metabolic specialization, biogeochemical processes and biotechnological advances. Growing evidence suggests that the presence of organelles is the rule, rather than the exception, in bacterial cells.
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Affiliation(s)
- Chris Greening
- Infection and Immunity Program, Biomedicine Discovery Institute and Department of Microbiology, Monash University, Clayton, Australia.
| | - Trevor Lithgow
- Infection and Immunity Program, Biomedicine Discovery Institute and Department of Microbiology, Monash University, Clayton, Australia.
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Perturbation of bacteriochlorophyll molecules in Fenna–Matthews–Olson protein complexes through mutagenesis of cysteine residues. BIOCHIMICA ET BIOPHYSICA ACTA-BIOENERGETICS 2016; 1857:1455-1463. [DOI: 10.1016/j.bbabio.2016.04.007] [Citation(s) in RCA: 24] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/12/2016] [Revised: 04/19/2016] [Accepted: 04/20/2016] [Indexed: 11/19/2022]
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Orf GS, Saer RG, Niedzwiedzki DM, Zhang H, McIntosh CL, Schultz JW, Mirica LM, Blankenship RE. Evidence for a cysteine-mediated mechanism of excitation energy regulation in a photosynthetic antenna complex. Proc Natl Acad Sci U S A 2016; 113:E4486-93. [PMID: 27335466 PMCID: PMC4978306 DOI: 10.1073/pnas.1603330113] [Citation(s) in RCA: 32] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023] Open
Abstract
Light-harvesting antenna complexes not only aid in the capture of solar energy for photosynthesis, but regulate the quantity of transferred energy as well. Light-harvesting regulation is important for protecting reaction center complexes from overexcitation, generation of reactive oxygen species, and metabolic overload. Usually, this regulation is controlled by the association of light-harvesting antennas with accessory quenchers such as carotenoids. One antenna complex, the Fenna-Matthews-Olson (FMO) antenna protein from green sulfur bacteria, completely lacks carotenoids and other known accessory quenchers. Nonetheless, the FMO protein is able to quench energy transfer in aerobic conditions effectively, indicating a previously unidentified type of regulatory mechanism. Through de novo sequencing MS, chemical modification, and mutagenesis, we have pinpointed the source of the quenching action to cysteine residues (Cys49 and Cys353) situated near two low-energy bacteriochlorophylls in the FMO protein from Chlorobaculum tepidum Removal of these cysteines (particularly removal of the completely conserved Cys353) through N-ethylmaleimide modification or mutagenesis to alanine abolishes the aerobic quenching effect. Electrochemical analysis and electron paramagnetic resonance spectra suggest that in aerobic conditions the cysteine thiols are converted to thiyl radicals which then are capable of quenching bacteriochlorophyll excited states through electron transfer photochemistry. This simple mechanism has implications for the design of bio-inspired light-harvesting antennas and the redesign of natural photosynthetic systems.
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Affiliation(s)
- Gregory S Orf
- Department of Chemistry, Washington University in St. Louis, St. Louis, MO 63130; Department of Biology, Washington University in St. Louis, St. Louis, MO 63130; Photosynthetic Antenna Research Center, Washington University in St. Louis, St. Louis, MO 63130
| | - Rafael G Saer
- Department of Biology, Washington University in St. Louis, St. Louis, MO 63130; Photosynthetic Antenna Research Center, Washington University in St. Louis, St. Louis, MO 63130
| | - Dariusz M Niedzwiedzki
- Photosynthetic Antenna Research Center, Washington University in St. Louis, St. Louis, MO 63130
| | - Hao Zhang
- Department of Chemistry, Washington University in St. Louis, St. Louis, MO 63130; Photosynthetic Antenna Research Center, Washington University in St. Louis, St. Louis, MO 63130
| | - Chelsea L McIntosh
- Department of Biology, Washington University in St. Louis, St. Louis, MO 63130
| | - Jason W Schultz
- Department of Chemistry, Washington University in St. Louis, St. Louis, MO 63130
| | - Liviu M Mirica
- Department of Chemistry, Washington University in St. Louis, St. Louis, MO 63130
| | - Robert E Blankenship
- Department of Chemistry, Washington University in St. Louis, St. Louis, MO 63130; Department of Biology, Washington University in St. Louis, St. Louis, MO 63130; Photosynthetic Antenna Research Center, Washington University in St. Louis, St. Louis, MO 63130
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Tsukatani Y, Mizoguchi T, Thweatt J, Tank M, Bryant DA, Tamiaki H. Glycolipid analyses of light-harvesting chlorosomes from envelope protein mutants of Chlorobaculum tepidum. PHOTOSYNTHESIS RESEARCH 2016; 128:235-241. [PMID: 26869354 DOI: 10.1007/s11120-016-0228-z] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/08/2015] [Accepted: 01/25/2016] [Indexed: 06/05/2023]
Abstract
Chlorosomes are large and efficient light-harvesting organelles in green photosynthetic bacteria, and they characteristically contain large numbers of bacteriochlorophyll c, d, or e molecules. Self-aggregated bacteriochlorophyll pigments are surrounded by a monolayer envelope membrane comprised of glycolipids and Csm proteins. Here, we analyzed glycolipid compositions of chlorosomes from the green sulfur bacterium Chlorobaculum tepidum mutants lacking one, two, or three Csm proteins by HPLC equipped with an evaporative light-scattering detector. The ratio of monogalactosyldiacylglyceride (MGDG) to rhamnosylgalactosyldiacylglyceride (RGDG) was smaller in chlorosomes from mutants lacking two or three proteins in CsmC/D/H motif family than in chlorosomes from the wild-type, whereas chlorosomes lacking CsmIJ showed relatively less RGDG than MGDG. The results suggest that the CsmC, CsmD, CsmH, and other chlorosome proteins are involved in organizing MGDG and RGDG and thereby affect the size and shape of the chlorosome.
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Affiliation(s)
- Yusuke Tsukatani
- Earth-Life Science Institute, Tokyo Institute of Technology, 2-12-1 Ookayama, Meguro, Tokyo, 152-8550, Japan.
- PRESTO, Japan Science and Technology Agency, Saitama, 332-0012, Japan.
| | - Tadashi Mizoguchi
- Graduate School of Life Sciences, Ritsumeikan University, Shiga, 525-8577, Japan
| | - Jennifer Thweatt
- Department of Biochemistry and Molecular Biology, The Pennsylvania State University, Pennsylvania, 16802, USA
| | - Marcus Tank
- Department of Biochemistry and Molecular Biology, The Pennsylvania State University, Pennsylvania, 16802, USA
| | - Donald A Bryant
- Department of Biochemistry and Molecular Biology, The Pennsylvania State University, Pennsylvania, 16802, USA
- Department of Chemistry and Biochemistry, Montana State University, Montana, 59717, USA
| | - Hitoshi Tamiaki
- Graduate School of Life Sciences, Ritsumeikan University, Shiga, 525-8577, Japan
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