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Unité d’Enseignement : Evolution du Phytoplancton Marin et Biogéochimie Introduction to Photosynthesis: Evolutionary processes Christophe Six UMR UPMC-CNRS 7144 “Adaptation & Diversité en Milieu Marin" Equipe « Procaryotes Photosynthétiques Marins » Station Biologique de Roscoff Université Pierre et Marie Curie (Paris VI) Bureau 354, 3ème étage (Bâtiment GT) [email protected] What is photosynthesis ? Sensu lato: Any synthesis of organic matter that is light dependent Common Sense: All processes used by phototrophic organisms using chlorophyll compounds to convert light energy into chemical energy (ATP). h Minerals Cofactors Organic matter . Most of life on Earth is dependent on photosynthesis through food webs. Exception : hydrothermal vents Origin of photosynthesis at the scale of Geological times Precambrian Millions years Millions years Millions years http://www.ipgp.jussieu.fr/files_lib/83_echm-gt.gif The oldest fossils : the Stromatolites Stromatolites Microfossils of filamentous cyanobacteria West of Australia http://www.interet-general.info/IMG/Stromatolites-2-3.jpg http://www.gc.maricopa.edu/earthsci/imagearchive/stromatolite.jpg http://www.cartage.org.lb/en/themes/Sciences/Paleontology/Paleozoology/Precambrian/Precambrian.htm Fossil evidences : the stratified iron formations Iron stratified formations Microbial coccoid fossil (Eosphaera) Mont Bruce, West of Australia http://www.geo.vu.nl/~smit/hamersley/hamersley%20iron.jpg 10 µm Formation of Gunflint, North America http://gsc.nrcan.gc.ca/paleochron/05_e.php http://z.about.com/d/geology/1/0/d/-/1/bifslab.jpg http://www.cartage.org.lb/en/themes/Sciences/Paleontology/Paleozoology/Precambrian/mich03.gif Consequences of the development of oxygenic photosynthesis Diversité (nombre de taxa) Billion years Présent The photosynthetic organisms on Earth . Sulphurous green bacteria Chlorobium, Prosthecochloris, Pelodictyon, Ancalochloris, Chloroherpeton . Non-sulphurous green bacteria Chloroflexus, Chloronema, Heliothrix, Roseiflexus . Non-Sulphurous purple bacteria Rhodospirillum, Rhodobacter, Rhodopseudomonas, Rhodomicrobium . Sulphurous purple bacteria Chromatium, Thiospirillum, Thiopedia Lakes & Estuaries Benthic/Planctonic. Stratified freshwater lakes: Anoxiques zones . Les heliobacteria Heliobacterium . Photoheterotrophic, anoxygenic, aerobic bacteria Roseobacter, Roseovarius, Erythrobacter Still poorly known; Oceans . Cyanobacteria = Oxyphotobacteria Synechococcus, Prochlorococcus, Oscillatoria, Anabaena, Synechocystis, Microcystis, Planktothrix, Trichodesmium, Croccosphaera, etc… . Photosynthetic (oxygenic) eukaryotes Rhodophyta, Heterokontophyta, Chlorobionta The different groups of photosynthetic organisms on Earth Photosynthesis Oxygenic Two types of reaction centres Antenna = Phycobilisome or Lhc Electron donnors = H2O Anoxygenic A single type of reaction centre -Typical antenna system (BChl & Carotenoids) Electron donnors = reduced compounds Aérobic RC I + RC II Cyanobacteria = oxyphotobacteria (photohétérotrophs & obligatory phototrophs) Aerobic Anaerobic Photosynthetic eukaryotes: Eukaryotic phytoplankton, macroalgae, bryophytes and vascular plants (photohétérotrophs) Purple bacteria (RC II – BChl a ou b – (Calvin cycle) Sulphurous (obligatory phototrophs) Non- sulphurous (photoheterotrophs) Green bacteria Héliobacteria (Chlorosome – no RuBisCO) RC I Sulphurous (obligatory phototrophs) RC I Chlorobiaceae Non- sulphurous (photoheterotrophs) RC II Chloroflexaceae Anoxygenic photosyntheses Reaction centres and bacteriochlorophylls Bactériochlorophylle a Bactériochlorophylle b Sulphurous Green bacteria Microbial mat : Chlorobium Chlorobium sp. BS1 Chlorobium tepidum Yellowstone national park, USA Microbewiki Benthic organisms : 1mm beneath the sediment at the bottom of lakes and estuaries The antenna complex of Chlorobium spp. The reaction centre of Chlorobium spp. . 3 proteins : 2 proteins A (65 kDa) + 1 small proteine C de 8 kDa Cofactors linked to these proteins constituting a double, transmembrane, redox chain . Charge separation: expulsion of an e- from a Bchl a P840, . Transfer to an acceptor A0 which has a low redox potential, then to A1 = naphtoquinone The reaction centre of Chlorobium spp. . Electron tranfer to three Iron-Sulphur clusters, named FX, FA et FB . 2 ferredoxins 2 e- + NAD+ + H+ NADH (universal reductant of metabolic reactions) => 2 excitons are necessary to produce one molecule of NADH Fd soluble Le centre réactionnel de Chlorobium spp. . Cytochromic system c553 : complexed (4 hemes) or soluble e- given back to P840 . c553 reduced by flavocytochrome c551 (1 heme + 1 flavin group) . 2 C551 + S2- C551 + 2 e- + S Sulphur is released in the periplasm The electron carrier chain of Chlorobium spp. Cyclic transport of e- Non-sulphurous purple bacteria Rhodospirillum rubrum Rhodobacter sphaeroides http://www.de.mpi-magdeburg.mpg.de/research/projects/1010/1014/1020/rhodos.jpg http://www.martin-stein.com/images/rhodob.jpg Rhodopseudomonas sp. Non-sulphurous purple bacteria Rhodobacter sp. Different types of structures of inner foldings of the plasmic membrane The inner foldings of Rhodobacter sphaeroides (chromatophores) The antenna complex of Rhodopseudomonas acidophila - LH2 complex : hollow cylinder constituted by 9 motifs = 9 paires de polypeptide et (5-7 kDa) - The 9 are in periphery, the 9 are inner ; bacteriochlorophylls are located between these two crowns - On pair binds 1 ou 2 BChl 18 BChl perpendicular to the plan per LH2 (= B850 abs max at 850nm) - The subunits bind an additional molecule of BChl between two -helices, parallel to the plan These 9 BChl = B800 (abs max à 800nm) - One carotenoid is linked to each Bleu : Polypeptides Orange : B800 bacteriochlorophylls Vert : Carotenoids The reaction centre of non-sulphurous purple bacteria Rhodobacter sphaeroides Rhodopseudomonas viridis Photosynthetic apparatus of Rhodobacter sp. Protein Structure involved in the photosynthetic activity of Rhodobacter sp. (Cross section of the cytoplasmic membrane) Cyclic electron transport in Rhodobacter sp. Anoxygenic reaction centres Oxygenic photosynthesis Oxygenic photosynthesis Global reaction : n [CO2 + H2O] [CH2O] n + O2 Location : Chloroplasts of vascular plants Marine chloroplasts Bryopsis sp. Porphyridium sp. Fucus sp. Synechococcus sp. Photosynthetic membranes : the thylacoids Stroma/cytosol Lumen Stroma/cytosol Membranar lipids The membranar photosynthetic complexes What is a photosystem? Photosystem = reaction centre + photosynthetic antenna . Two large subunits D1/D2 ; PsaAB) . A number of small subunits . External antenna : the major one . Inner antenna stuck to the reaction centre : the minor one . The charge separation : one electron is extracted from a chlorophyll molecule and released in a chain of acceptors Chl (=P680) chl* (=P680*) + e- Photosystem II antennae . Large diversity of configuration depending on the taxonomic group . Two major structural groups : intrinsic et extrinsic to the thylacoids Intrinsic antennae Intrinsic, major PSII antenna (LHC type) Thylacoids PS LHC type proteins Intrinsic antennae CP43 D1/D2 CP47 CP43 Proteins LHC D1/D2 CP47 Reaction centres Lhcb3 ou 4 ou 5 ou 6 Trimères de LHCIIb (Top view) Pigments associated to intrinsic antennae . Chemotaxonomy Chl a 19'-hexanoyloxyfucoxanthin Chl b Chl c1 Lutein Chl c2 Neoxanthin Chl c3 Prasinoxanthin Fucoxanthin Peridinin . Different roles of the xanthophylls: light harvesting & photoprotection Violaxanthin Antheraxanthin Zeaxanthin Diadinoxanthin Diatoxanthin Pigments associated to intrinsic antennae Chlorophylls a et b Absorption properties of chlorophylls Chl c Carotenoids -carotene (vitamin A) -carotene Carotenoids: xanthophylls Carotenoids: absorption properties -Carotene Fucoxanthin Lutein Zeaxanthin Diadinoxanthin Organisms with extrinsic, photosynthetic antennae Rhodophyta Cyanophyta Cryptophyta Phycobiliproteins Phycobiliproteins . 4 classes of phycobiliproteins : Allophycocyanin (AP) Phycocyanin (PC) Phycoérythrocyanin (PEC) Phycoérythrin (PE) . The classes of phycobiliproteins are differentiatated by: - The aminoacid sequence of the and chains (between 15 and 20 kDa) - The composition in phycobilins, and therefore their spectral properties . 4 classes of phycobilins : Phycocyanobilin (PCB) Phycobiliviolin (PVB) Phycoérythrobilin (PEB) Phycourobilin (PUB) Phycobilins Phycourobilin Phycoerythrobilin Phycyanobilin Phycobilin Biosynthesis Glutamyl-ARNt Glutamate semi aldéhyde Acide aminolevulinique Uroporphyrinogène III Protoporphyrine IX + Fe Hème oxygénase Hème Biliverdine Dihydrobiliverdine Phycobilines Mg Chl bactériochl Catalases Cytochromes Phycobiliproteins and phycobilins αPC A 84 βPC 162 PCB B 84 155 C-PC : A=B=PCB PVB B=PCB PEC : A=PXB, R-PCI : A=PCB, B=PEB R-PCII : A=B=PEB R-PCIII : A=B=PEB R-PC IV : A = PUB Phycoerythrins 172 Chromophores donnor vs. Chromophore acceptor The phycobilin placed at -84 Is always the acceptor chromophore, whatever the phycobiliprotein Phycobiliproteins and phycobilins 250/61 282 140 282 PEII dimer 282 Hexameric PEII diagram Modified after Wilbanks et al. (1991) Synechococcus sp. WH8103 Optical properties of phycobiliproteins Absorbance Absorption Fluorescence PCB PEB C A Wavelength (nm) Wavelength (nm) C-Phycocyanin C D PUB PEB D E E F The phycobilisome . Phycobiliprotein hexamers aggregate in macrostructures: Allophycocyanin Phycoerythrin Phycocyanin 11 nm 6 nm coeur Bras Hexamer ()6 Phycobilisomes of Calothrix sp. PCC 7601 (Sidler, 1994) Phycobilisome linker polypeptides Subunits & SDS-PAGE (15% acr.) of phycobilisomes fractions Synechococcus sp. PCC7002 (1), Anabaena sp. PCC7120 (2), Mastigocladus laminosus (3) ; Weigh markers (4). Linkers (M. laminosus, Reuter and Nickel-Reuter, 1993) Oriented transport of energy in the phycobilisome Phycobilisomes constantly diffuse on thylacoids Photosystem II structure Photosystem II structure Photosystem I structure How does oxygenic photosynthesis work? How does oxygenic photosynthesis work? Oxygenic photosynthesis