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Spectroscopic Study of the CP43′ Complex and the PSI–CP43′ Supercomplex of the Cyanobacterium Synechocystis PCC 6803

AuthorsFeng, Ximao; Neupane, Bhanu; Acharya, Khem; Zazubovich, Valter; Picorel Castaño, Rafael CSIC ORCID ; Seibert, Michael; Jankowiak, Ryszard J.
KeywordsHole Burning
Fluorescence Excitation
Excitation Energy Transfer
Issue DateNov-2011
PublisherAmerican Chemical Society
CitationFeng X, Neupane B, Acharya K, Zazubovich V, Picorel RE, Seibert M, Jankowiak R. Spectroscopic Study of the CP43′ Complex and the PSI–CP43′ Supercomplex of the Cyanobacterium Synechocystis PCC 6803. Journal of Physical Chemistry B 115 (45): 13339–13349 (2011)
AbstractThe PSI-CP43' supercomplex of the cyanobacterium Synechocystis PCC 6803, grown under iron-starvation conditions, consists of a trimeric core Photosystem I (PSI) complex and an outer ring of 18 CP43' light-harvesting complexes. We have investigated the electronic structure and excitation energy transfer (EET) pathways within the CP43' (also known as the isiA gene product) ring using low-temperature absorption, fluorescence, fluorescence excitation, and hole-burning (HB) spectroscopies. Analysis of the absorption spectra of PSI, CP43', and PSI-CP43' complexes suggests that there are 13 chlorophylls (Chls) per CP43' monomer, i.e., a number that was observed in the CP43 complex of Photosystem 11 (PSII) (Umena, Y. et al. Nature 2011, 473, 55-60). This is in contrast with the recent modeling studies of Zhang et al. (Biochim. Biophys. Acta 2010, 1797, 457-465), which suggested that IsiA likely contains 15 Chls. Modeling studies of various optical spectra of the CP43' ring using the uncorrelated EET model (Zazubovich, V.; Jankowiak, R J. Lumin. 2007, 127, 245-250) suggest that CP43' monomers (in analogy to the CP43 complexes of the PSII core) also possess two quasi-degenerate low-energy states, A' and B'. The site distribution functions of states A' and B' maxima/full width at half-maximum (fwhm) are at 684 nm/180 cm(-1) and 683 nm/80 cm(-1), respectively. Our analysis shows that pigments mostly contributing to the lowest-energy A' and B' states must be located on the side of the CP43' complex facing the PSI core, a finding that contradicts the model of Zhang et al. but is in agreement with the model suggested by Nield et al. (Biochemistry 2003, 42, 3180-3188). We demonstrate that the A'-A' and B'-B' EET between different monomers is possible, though with a slower rate than intramonomer A'-B' and/or B'-A' energy transfer.
Description8 Pags. The definitive version, with Figs., is available at: http://pubs.acs.org/journal/jpcbfk
Publisher version (URL)http://dx.doi.org/10.1021/jp206054b
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