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 ・ Scheme of the energy dissipation mechanism ・ Measurement of the NIR transient absorption ・ Specification the position of energy dissipation Conclusion

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

Scheme of the energy dissipation mechanism hν Chl * * Chl-Zea + Chl ・－ Zea ・ ＋ Chl-Zea photosynthetic reaction center ~ ~ Energy dissipation N. E. Holt et al., Science 307, 433 (2005).

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

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

NIR transient absorption kinetics Red : CP29-Zea Black : CP29-Vio Blue : Subtraction of Red from Black

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

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

Sample ~ a series of mutant CP29 complexes ~ L1 site : Lutein L2 site : Zea or Vio ・ CP29 each lacking specific chlorophylls CP29 -A1 ( unstable ) CP29 -A2 CP29 -A3 CP29 -A4 CP29 -A5 ( also loss of B5 ) CP29 -B3 CP29 -B5 ( lacking B5 only ) CP29 -B6 lack Far away

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

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

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). Strongly coupled to each other Zeaxanthin

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.