Increasing Absorption Range for Photosynthesis

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Increasing Absorption Range for Photosynthesis
http//media-2.web.britannica.com/eb-media/30/2703
0-004-293E0372.jpg
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Goals

• Express different photosynthetic pigments in
  cyanobacteria
• Increase the wavelengths that can absorb light
  energy and transfer to photosynthetic machinery
• Potentially increase efficiency?

http//www.emc.maricopa.edu/faculty/farabee/BIOBK/
pigment.gif
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Photosynthetic Pigments
Chlorophylls
Phycobilins
? carotene
Carotenoids
http//www.food-info.net/uk/colour/chlorophyll.htm
http//www.mbari.org/staff/conn/botany/reds/daisy/
phycocyanobilin.gifhttp//upload.wikimedia.org/wi
kipedia/commons/d/da/Beta-carotene.png
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How do the Photo-Pigs work?

• Chlorophylls
• Transfers electrons around ? reaction center
• Incorporated into photosystem protein complexes
• Carotenoids
• Membrane bound
• Transfers electrons to chlorophyll
• Phycobilins
• Water soluble, in cytoplasm
• Also transfers electrons to chlorophyll

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Model Organism Cyanobacteria

• Synechococcus, Synechocystis sp. PCC6803
• Chlorophyll a, Phycobilins (phycocyanin,
  allophycocyanin, allophycocyanin B,
  phytoerythrin)
• Genetically tractable

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What has been done before?

• Expressed chlorophyll b in Synechocystis sp.
  PCC6803
• Demonstrated that it is incorporated into P700
  chlorophyll-protein complex

Satoh et al., Journal of Biological Chemistry,
2001 276 (6)
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What can we do?
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Idea 1 BioBrick Bba_K152005

• Four enzymes required for beta-carotene
  synthesis
• geranylgeranyl diphosphate synthase (CrtE -
  BbaK152001)
• phytoene synthase (CrtB - BbaK152002)
• phytoene dehydrogenase (CrtI - BbaK18003)
• lycopene beta-cyclase (CrtY - BbaK152003)

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Carotenoid Biosynthesis in Synechococcus
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Questions to ask / Things to do

• When overexpressed is beta-carotene incorporated
  into a photosystem?
• What does beta-carotene normally do in
  cyanobacteria?
• How/Why was this biobrick made? What did they
  feed the E. coli?
• Can E. coli constructs be used in cyanobacteria?

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Idea 2 Express Chlorophyll d

• Spectrum is red shifted
• Can act as reaction center?
• Need to find protein that cando this reaction.

Larkum and Kuhl, Trends in Plant Science (2005)
10 (8).