Master Seminar
Julian Taffner
„Structure-Function Analysis of
Photosystem II
for Biofuel Production with
Cyanobacteria“
Supervisor
Prof. G. Kohring
Prof. J. Eaton-Rye
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High potential of photosynthesis
• > 3,5 billions of years: first photosynthetic organisms
• 2 billions of years: first photosynthetic organims
producing oxygen
• Without photosynthesis: total extinction of higher
life within 25 years (like 65 million years ago)
• > 4,2 x 1017 kJ of free enthalpy stored by
Photosynthesis per year
 1010 tons of carbon
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Photosynthesis
• Process to convert light energy into chemical energy
(carbohydrates)
• Photoautotrophes like algae, plants, cyanobacteria
• Chlorophyll pigments catching the light energy
• Electrons become excited on higher energy level
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Stryer Biochemie 6.Auflage
Photosynthesis II
• General equation:
CO2 + H2O  (CH2O) + O2
• Used in „light-reaction“ to produce
– NADPH
– Proton gradient for ATP synthesis
– O2
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http://www.quia.com/files/quia/users/lmcgee/plants/photosynthesis/photosynthesis-L.gif
Photosynthesis in plants and algae
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5µm long
Inner and outer membrane
Special membrane-structure, called thylakoids
Stacked together to grana
Not autonomic
Particular DNA
http://www.buzzle.com/images/diagrams/chloroplast.jpg
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Photosynthesis in Cyanobacteria
• Oxygen phototroph
• Takes place in thylakoid-membrane
Endosymbiotic event of Cyanobacteria ancestor and
ancestral procaryote
similar to mitochondrial endosymbiosis
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http://www.ib.bioninja.com.au/_Media/endosymbiosis_med.jpeg
Light absorption: Chlorophyll a
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Main step in photosynthesis
In green plants and algae
Tetrapyrrol with Mg in the center
Alternation of single and double bonds
 variation in absorption spectrum
Extinction coefficient of
10^5 M^-1 cm^-1
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http://en.wikipedia.org/wiki/Chlorophyll_a
http://blog.captive-aquatics.com/.a/6a010535f11c3d970c015434697eb6970c-800wi
Light absorption: Bacteriochlorophyll b
• In Cyanobacteria
• Similar to chlorophyll a
• Absorption up to 1000 nm
http://en.wikipedia.org/wiki/Bacteriochlorophyll
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Light absorption: mechanism
• Electron becomes excited by a photon in reaction center
• Raised to a higher energy state in electron configuration
• Usually emission of energy when falling back to lower
level
• BUT existence of an electron acceptor
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http://www.biokurs.de/skripten/bilder/Anreg2.GIF
http://www.u-helmich.de/bio/stw/reihe4/licht/images/chloro03.gif
Photosynthetic reaction center in
bacteria
Stryer; figure 19.9;page 608
L - red
M – blue
H-chain – white
Cyt. Subunit - yellow
• Light absorption takes place in
photosynthetic reaction center
• Best analyzed in
Rhodopseudomonas viridis with
atomic resolution
• 4 polypeptide chains: L-, M- and Hsubunit and Cytochrom C with 4
heme molecules
• Homolog to complex system of the
plants
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Electron transfer in bacterial reaction
center
Stryer; picture 19.10; page 609
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Photosystem II
Stryer
Bild 19.13
Seite 612
• Transmembrane complex
• Composts of 20 protein subunits
and 80 cofactors
• Electron transfer from water to
plastoquinone
• Production of a proton gradient
Govindjee et al., 2010
2Q + 2H2O  O2 + 2QH2
Q=
oxidized plastoquinone
QH2= reduced plastoquinone
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Electron transfer in photosystem II
Stryer
Bild 19.14
• Light absorption at P680
• Electron transfer to pheophytin
• Further transfer to bound
plastoquinone (in QA position) and
then to mobile plastoquinone (QB)
• Neutralisation of P680+ charge by
electron transfer over manganese
cluster from water
 bacterial system
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Photosystem I
• Electron transfer to PS I by Cytochrome bf
• Consists of 14 polypeptide chains and
associated proteins and cofactors
• P700 absorbs light to produce ferredoxin
• Ferredoxin-NADP+-Reductase catalyses NADPH
production
• Proton gradient leads to ATP-synthesis by ATPsynthase
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Application in biofuel production
Sun provides more energy in 1 h than our entire
global energy consumption in 1 year
Biological conversion of CO2 to biofuel by microorganisms
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Microalgae and Cyanobacteria
High photosynthetic efficiency
Higher growth rate
Production on non-arable land
Advancements of synthtetic biology
and genetic manipulation
http://www.savingwater.co.za/wpcontent/uploads/2011/02/algae-biofuel.jpg
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Department of biochemistry
in Otago
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Department of biochemistry
Prof. J. Eaton-Rye
• Structure-function analysis of
photosystem II
• Protein-protein interactions that facilitate
sustained water-splitting activity
in response to environmental changes
• Protein factors required for the assembly
of PS II
• Metabolic engineering of photosynthetic
protein complexes for efficient biofuel
production in cyanobacteria
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My project
• Function of the Psb30, PsbK and PsbZ
proteins belonging to the CP43-Psb27
pre-complex
• Gene knockouts to create single and
double mutants
• Effects on assembly and function of
Photosystem II
Nickelsen et al., 2013
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Importance of the project
• Psb30, PsbK and PsbZ are highly conserved as
part of the CP43-Psb27 complex
• Psb27 stabilizes and protects CP43
 supports rapid PSII repair after photodamage
• As part of PSII crucial for water splitting reaction
(proton, electron and oxygen production)
• Metabolic engineering to optimize efficiency of
photosystem II
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Thank you
for your
attention
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Sources
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„Structure and function of the hydrophilic Photosystem II assembly proteins:
Psb27, Psb28 and Ycf48“; Peter D. Mabbitt, Sigurd M. Wilbanks, Julian J. EatonRye*
„Cyanobacteria biofuel production“; Iara M.P. Machado, Shota Atsumi
„Photosystem II Assembly: From Cyanobacteria to Plants“; Jörg Nickelsen and Birgit
Rengstl
„Photosystem II“ ; Govindjee, Jan F Kern, Johannes Messinger, John Whitmarsh
Stryer 6.Auflage
“The PsbK Subunit is Required for the Stable Assembly and Stability of Other Small
Subunits in the PSII complex in the Thermophilic Cyanobacterium
Thermosynechococcus elongatus BP-1”; Iwai et al., 2010
http://biology.clc.uc.edu/courses/bio104/photosyn.htm
http://www.spektrum.de/lexikon/biologie-kompakt/cyanobakterien/2758
http://www.plantphysiol.org/content/early/2011/11/15/pp.111.184184.full.pdf
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