Christophe Six

UMR UPMC-CNRS 7144 “Adaptation & Diversité en Milieu Marin"Equipe « Procaryotes Photosynthétiques Marins »

Station Biologique de RoscoffUniversité Pierre et Marie Curie (Paris VI)

Bureau 354, 3ème étage (Bâtiment GT)six@sb-roscoff.fr

Unité d’Enseignement : Evolution du Phytoplancton Marin et Biogéochimie

Introduction to Photosynthesis:Evolutionary processes

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).

Organic matter

MineralsCofactors

h

. Most of life on Earth is dependent on photosynthesis through food webs. Exception : hydrothermal vents

Origin of photosynthesis at thescale of Geological times

Millio

ns years

Precambrian

http://www.ipgp.jussieu.fr/files_lib/83_echm-gt.gif

Millio

ns

ye

ars

Millio

ns

ye

ars

Stromatolites

http://www.cartage.org.lb/en/themes/Sciences/Paleontology/Paleozoology/Precambrian/Precambrian.htm

West of Australiahttp://www.interet-general.info/IMG/Stromatolites-2-3.jpghttp://www.gc.maricopa.edu/earthsci/imagearchive/stromatolite.jpg

Microfossils of filamentouscyanobacteria

The oldest fossils : the Stromatolites

Microbial coccoid fossil (Eosphaera)

Formation of Gunflint, North Americahttp://gsc.nrcan.gc.ca/paleochron/05_e.php

10 µm

Fossil evidences : the stratified iron formations

Mont Bruce, West of Australiahttp://www.geo.vu.nl/~smit/hamersley/hamersley%20iron.jpg

Iron stratified formations

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

Formation couche d’ozone

Radiationcyanobactérienne

Formation couche d’ozone

Formation couche d’ozone

Radiationcyanobactérienne

Bil

lio

n y

ear

s

Diversité (nombre de taxa)Présent

Consequences of the development of oxygenic photosynthesis

. 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

. Les heliobacteria Heliobacterium

. Photoheterotrophic, anoxygenic, aerobic bacteria Roseobacter, Roseovarius, Erythrobacter

. Cyanobacteria = Oxyphotobacteria Synechococcus, Prochlorococcus, Oscillatoria, Anabaena, Synechocystis, Microcystis, Planktothrix, Trichodesmium, Croccosphaera, etc…

. Photosynthetic (oxygenic) eukaryotes Rhodophyta, Heterokontophyta, Chlorobionta

The photosynthetic organisms on Earth

Lakes & Estuaries

Benthic/Planctonic.Stratified freshwater lakes: Anoxiques zones

Still poorly known; Oceans

The different groups of photosynthetic organisms on Earth

Photosynthesis

Oxygenic

Anoxygenic

A single type of reaction centre-Typical antenna system (BChl & Carotenoids)

Electron donnors = reduced compounds

Two types of reaction centresAntenna = Phycobilisome or Lhc

Electron donnors = H2O

AnaerobicAerobic(photohétérotrophs)

RC I + RC IICyanobacteria = oxyphotobacteria

(photohétérotrophs & obligatory phototrophs)

Photosynthetic eukaryotes:Eukaryotic phytoplankton, macroalgae,

bryophytes and vascular plants

Aérobic

Purple bacteria(RC II – BChl a ou b – (Calvin cycle)

Sulphurous(obligatory

phototrophs)

Non- sulphurous(photoheterotrophs)

Green bacteria(Chlorosome – no RuBisCO)

Sulphurous(obligatory

phototrophs)RC I

Non- sulphurous(photoheterotrophs)

RC II

Chlorobiaceae Chloroflexaceae

HéliobacteriaRC I

Anoxygenic photosyntheses

Reaction centres and bacteriochlorophylls

Bactériochlorophylle a Bactériochlorophylle b

Sulphurous Green bacteria

Chlorobium tepidumMicrobial mat : Chlorobium

Yellowstone national park, USAMicrobewiki

Chlorobium sp. BS1

Benthic organisms : 1mm beneath the sediment at the bottomof 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

. 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

The reaction centre of Chlorobium spp.

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

http://www.martin-stein.com/images/rhodob.jpg

Rhodobacter sphaeroides

Rhodospirillum rubrum

http://www.de.mpi-magdeburg.mpg.de/research/projects/1010/1014/1020/rhodos.jpg

Rhodopseudomonas sp.

Rhodobacter sp.

Different types of structures of inner foldings

of the plasmic membrane

Non-sulphurous purple bacteria

The inner foldings of Rhodobacter sphaeroides (chromatophores)

The antenna complex of Rhodopseudomonas acidophila

- On pair binds 1 ou 2 BChl 18 BChl perpendicular to the plan per LH2 (= B850 abs max at 850nm)

- 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

- 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 : PolypeptidesOrange : B800 bacteriochlorophyllsVert : Carotenoids

Rhodobacter sphaeroides

Rhodopseudomonas viridis

The reaction centre of non-sulphurous purple bacteria

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

Global reaction : n [CO2 + H2O] [CH2O] n + O2

Location :

Chloroplasts ofvascular plants

Oxygenic photosynthesis

Bryopsis sp. Porphyridium sp. Fucus sp. Synechococcus sp.

Marine chloroplasts

Photosynthetic membranes : the thylacoids

Stroma/cytosol

Stroma/cytosolLumen

Membranar lipids

The membranar photosynthetic complexes

What is a photosystem?

. Two large subunits D1/D2 ; PsaAB)

. A number of small subunits

Photosystem = reaction centre + photosynthetic antenna

. 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

. Two major structural groups : intrinsic et extrinsic to the thylacoids

. Large diversity of configuration depending on the taxonomic group

PS

Intrinsic, major PSII antenna (LHC type)

Intrinsic antennae

LHC type proteins

Th

yla

co

ids

CP43

D1/D2

CP47

D1/D2

CP47

CP43

Trimères de LHCIIb

Lhcb3 ou 4 ou 5 ou 6

CP43

D1/D2

CP47

D1/D2

CP47

CP43

CP43

D1/D2D1/D2

CP47

D1/D2D1/D2

CP47

CP43

Trimères de LHCIIb

Lhcb3 ou 4 ou 5 ou 6

Trimères de LHCIIb

Lhcb3 ou 4 ou 5 ou 6

Reaction centres

Proteins LHC

Intrinsic antennae

(Top view)

Pigments associated to intrinsic antennae

Chl aChl b Chl c1

Chl c2

Chl c3

Violaxanthin

Antheraxanthin

Zeaxanthin

Diadinoxanthin

Diatoxanthin

Lutein

Neoxanthin

Prasinoxanthin

19'-hexanoyloxyfucoxanthin

Fucoxanthin

. Chemotaxonomy

. Different roles of the xanthophylls: light harvesting & photoprotection

Peridinin

Chlorophylls a et b

Pigments associated to intrinsic antennae

Chl c

Absorption propertiesof chlorophylls

-carotene (vitamin A)

-carotene

Carotenoids

Carotenoids: xanthophylls

-Carotene DiadinoxanthinFucoxanthin

Lutein Zeaxanthin

Carotenoids: absorption properties

Rhodophyta Cyanophyta

Organisms with extrinsic, photosynthetic antennae

Cryptophyta

Phycobiliproteins

. 4 classes of phycobiliproteins :

Allophycocyanin (AP)Phycocyanin (PC)Phycoérythrocyanin (PEC)Phycoérythrin (PE)

Phycobiliproteins

. 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

Chlbactériochl

CatalasesCytochromes

Mg

Hème oxygénase

Hème

Biliverdine

Dihydrobiliverdine

Phycobilines

Glutamyl-ARNt

Glutamate semi aldéhyde

Acide aminolevulinique

Uroporphyrinogène III

Protoporphyrine IX+ Fe

Chlbactériochl

CatalasesCytochromes

Mg

Hème oxygénase

Hème

Biliverdine

Dihydrobiliverdine

Phycobilines

Phycobiliproteins and phycobilins

αPC

βPC

162

17284

84

155

PCB

A

B

C-PC : A=B=PCBPEC : A=PXB, B=PCBR-PCI : A=PCB, B=PEBR-PCII : A=B=PEB

αPC

βPC

162

17284

84

155

PCB

A

B

C-PC : A=B=PCBPEC : A=PXB, B=PCBR-PCI : A=PCB, B=PEBR-PCII : A=B=PEBR-PCIII : A=B=PEBR-PC IV : A = PUB

PVB

αPC

βPC

162

17284

84

155

PCB

A

B

C-PC : A=B=PCBPEC : A=PXB, B=PCBR-PCI : A=PCB, B=PEBR-PCII : A=B=PEB

αPC

βPC

162

17284

84

155

PCB

A

B

C-PC : A=B=PCBPEC : A=PXB, B=PCBR-PCI : A=PCB, B=PEBR-PCII : A=B=PEBR-PCIII : A=B=PEBR-PC IV : A = PUB

αPC

βPC

162

17284

84

155

PCB

A

B

C-PC : A=B=PCBPEC : A=PXB, B=PCBR-PCI : A=PCB, B=PEBR-PCII : A=B=PEB

αPC

βPC

162

17284

84

155

PCB

A

B

C-PC : A=B=PCBPEC : A=PXB, B=PCBR-PCI : A=PCB, B=PEBR-PCII : A=B=PEBR-PCIII : A=B=PEBR-PC IV : A = PUB

PVB

Chromophores donnorvs.

Chromophore acceptor

The phycobilin placed at -84 Is always the acceptor chromophore,

whatever the phycobiliprotein

Phycoerythrins

757583

83

75

75

83

8375

75

83

83

159140159

140

140

159159

140

-159 159

140

-14

0

250/61

250/61

250

/61

282

282 282

Hexameric PEII diagram

Modified after Wilbanks et al. (1991)

PEII dimer

Synechococcus sp. WH8103

Phycobiliproteins and phycobilins

Optical properties of phycobiliproteins

Ab

so

rpti

on

Flu

ore

scen

ce

Wavelength (nm)

A

Ab

so

rpti

on

Flu

ore

scen

ce

Ab

so

rpti

on

Ab

so

rpti

on

Flu

ore

scen

ce

Wavelength (nm)

A

D E

C

F

G H

Ab

so

rpti

on

Flu

ore

scen

ce

Wavelength (nm)

A

Ab

so

rpti

on

Flu

ore

scen

ce

Ab

so

rpti

on

Ab

so

rpti

on

Flu

ore

scen

ce

Wavelength (nm)

A

D E

C

F

G H

C-Phycocyanin

Ab

sorb

ance

PCB PEB PEBPUB

Wavelength (nm)

The phycobilisome

Phycocyanin

Phycoerythrin

Bras

Allophycocyanin

coeur6 nm

11 nm

Hexamer ()6

. Phycobiliprotein hexamers aggregate in macrostructures:

Phycobilisomes of Calothrix sp. PCC 7601

(Sidler, 1994)

SDS-PAGE (15% acr.) of phycobilisomes fractions Synechococcus sp. PCC7002 (1),

Anabaena sp. PCC7120 (2), Mastigocladus laminosus (3) ;

Weigh markers (4).

LinkersSubunits &

(M. laminosus, Reuter and Nickel-Reuter, 1993)

Phycobilisome linker polypeptides

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