Structure-Based Exciton Hamiltonian and Dynamics for the Reconstituted Wild-type CP29 Protein Antenna Complex of the Photosystem II
- Kansas State University, Manhattan, KS (United States)
- Centro Studi sulla Biologia Cellulare e Molecolare delle Piante, Milano (Italy)
Here we provide an analysis of the pigment composition of reconstituted wild type CP29 complexes. The obtained stoichiometry of 9 ± 0.6 Chls a and 3 ± 0.6 Chls b per complex, with some possible heterogeneity in the carotenoid binding, is in agreement with 9 Chls a and 3.5 Chls b revealed by the modeling of low-temperature optical spectra. We find that ~50% of Chl b614 is lost during the reconstitution/purification procedure, while Chls a are almost fully retained. The excitonic structure and the nature of the low-energy (low-E) state(s) are addressed via simulations (using Redfield theory) of 5 K absorption and fluorescence/nonresonant hole-burned (NRHB) spectra obtained at different excitation/burning conditions. We show that, depending on laser excitation frequency, reconstituted complexes display two (independent) low-E states (i.e., the A and B traps) with different NRHB and emission spectra. The red-shifted state A near 682.4 nm is assigned to a minor (~10%) subpopulation (Sub. II) that most likely originates from an imperfect local folding occurring during protein reconstitution. Its lowest energy state A (localized on Chl a604) is easily burned with λB = 488.0 nm and has a red-shifted florescence origin band near 683.7 nm that is not observed in native (isolated) complexes. Prolonged burning by 488.0 nm light reveals a second low-E trap at 680.2 nm (state B) with a fluorescence origin-band ~681 nm which is also observed when using a direct lowfluence excitation near 650 nm. The latter state is mostly delocalized over the a611, a612, a615 Chl trimer, and corresponds to the lowest energy state of the major (~90%) subpopulation (Sub. I) which exhibits a lower hole-burning quantum yield. Thus, we suggest that major Sub. I correspond to the native folding of CP29, whereas the red-shift of the Chl a604 site energy observed in the minor Sub. II occurs only in reconstituted complexes.
- Research Organization:
- Kansas State Univ., Manhattan, KS (United States)
- Sponsoring Organization:
- USDOE Office of Science (SC), Basic Energy Sciences (BES). Chemical Sciences, Geosciences & Biosciences Division
- Grant/Contract Number:
- SC0006678
- OSTI ID:
- 1539195
- Journal Information:
- Journal of Physical Chemistry. B, Condensed Matter, Materials, Surfaces, Interfaces and Biophysical Chemistry, Vol. 122, Issue 17; ISSN 1520-6106
- Publisher:
- American Chemical SocietyCopyright Statement
- Country of Publication:
- United States
- Language:
- English
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