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Architecture of a Charge-Transfer State Regulating Light Harvesting in a Plant Antenna Protein

Architecture of a Charge-Transfer State Regulating Light Harvesting in a Plant Antenna Protein. Tae Kyu Ahn, et al. Science 320 , 794 (2008). Miyasaka Lab. Yuji Morii. Contents. Introduction 　　　・ Photosynthesis 　　　・ Photoprotective process Results and discussion

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Architecture of a Charge-Transfer State Regulating Light Harvesting in a Plant Antenna Protein

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  1. Architecture of a Charge-Transfer State Regulating Light Harvesting in a Plant Antenna Protein Tae Kyu Ahn, et al. Science320, 794 (2008) Miyasaka Lab. Yuji Morii

  2. Contents • Introduction 　　　・ Photosynthesis 　　　・ Photoprotective process • Results and discussion 　　　・ Scheme of the energy dissipation mechanism 　　　・ Measurement of the NIR transient absorption 　　　・ Specification the position of energy dissipation • Conclusion

  3. Chlorophyll Excess Light Light Energy Dissipation Reaction Center Antenna Zeaxanthin Convert light energy into electric energy Photosynthesis Light harvest Photosynthesis

  4. hν Chl ・－ * * + Chl Chl-Zea Chl-Zea Zea ・＋ photosynthetic reaction center Energy dissipation ~ ~ Scheme of the energy dissipation mechanism N. E. Holt et al., Science307, 433 (2005).

  5. E Violaxanthin Chl* Zeaxanthin Chl Xanthophyll cycle carotenoids Violaxanthin Antheraxanthin Lowlight Excesslight Zeaxanthin Energy dissipation is regulated by excess or limiting light. B.Demmig- Adams, W. W. Adams Ⅲ, Tends Plant Sci.1, 21 (1996).

  6. CP29 homology structure model A1-A5 : Chlorophyll a B3,B5,B6 : Chlorophyll b L1,L2 : Carotenoid-binding site

  7. NIR transient absorption kinetics Red : CP29-ZeaBlack : CP29-VioBlue : Subtraction of Red from Black

  8. NIR transient absorption spectrum Max : 980 nm The spectrum is in good agreement with the established Zea・+ absorption characteristics.

  9. Chl-Zea Chl ・－ hν * * + Chl Chl-Zea Zea ・＋ ~ ~ photosynthetic reaction center NIR transient absorption kinetics The different profile is indicative oftransient Zea・+formation. Energy dissipation

  10. Far away lack Sample ~ a series of mutant CP29 complexes ~ ・CP29 each lacking specific chlorophylls CP29-A1 (unstable)CP29-A2CP29-A3CP29-A4CP29-A5 (also loss of B5)CP29-B3CP29-B5(lacking B5 only)CP29-B6 L1 site : LuteinL2 site : Zea or Vio

  11. Kinetic profiles of CP29-A2 , -A3 , -A4, –B6 These kinetic profiles indicate the Zea・+ evolution. Energy dissipationis active.

  12. Kinetic profiles of CP29-B3 , -A5 , –B5 Energy dissipation is active. No measurable Z・+ formation signal Energy dissipation is inactive.

  13. Strongly coupled to each other Zeaxanthin Molecular detail of the CT quenching site The molecular site of CT quenching in CP29 comprises Z and a strongly coupled chlorophyll pair (A5 and B5).

  14. Conclusion • The primary event of CT quenching in CP29 involves electron transfer Zea to a strongly coupled chlorophyll dimer in the A5-B5 pocket of CP29, rather than from Zea to a monomeric chlorophyll molecule. • Controlling the coupling strength between chlorophylls A5 and B5 in CP29 would modulate the reduction potential of the chlorophyll dimer and therefore could be used to switch ON and OFF the CT quenching.

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