Site-directed mutations at D1-Thr179 of photosystem II in Synechocystis sp. PCC 6803 modify the spectroscopic properties of the accessory chlorophyll in the D1-branch of the reaction center.
D1-Thr179, which overlies the reaction center chlorophyll Chl D1 of Photosystem II was replaced with His and Glu through site-directed mutation in Synechocystis sp. PCC 6803. Spectroscopic characterization of the mutants indicates that, compared to wild type, the main bleaching in the triplet-minus-singlet absorbance difference spectrum and the electrochromic band shift in the (P680 (+)Q A (-)-P680Q A) absorbance difference spectrum are displaced to the red by approximately 2 nm in the D1-Thr179His mutant and to the blue by approximately 1 nm in the D1-Thr179Glu mutant. These difference spectra are compared with the absorbance difference spectra, measured on the same states in the D1-His198Gln mutant in which the axial ligand D1-His198 of the special pair chlorophyll, P D1, was replaced by glutamine. Together, these results give direct evidence that (a) the reaction center triplet state, produced upon charge recombination from (3)[P (+)Pheo (-)], is primarily localized on Chl D1; (b) the cation of the oxidized donor P (+) is predominantly localized on chlorophyll P D1 of the special pair; and (c) the Q Y band of the accessory chlorophyll Chl D1 is electrochromically shifted in response to charges on P (+) and Q A (-). Light-induced absorbance difference spectra (between 650 and 710 nm), associated with the oxidation of secondary donors and the reduction of Q A, exhibit a bleaching attributed to the oxidation of a Chl Z and strong electrochromic band shifts. On the basis of mutation-induced spectroscopic changes and of structure-based calculations, we conclude that the experimental spectra are best explained by a blue-shift of the Q Y band of the accessory chlorophyll Chl D1, arising from charges on Car D2 (+) and Chl ZD2 (+) and on reduced Q A.
Schlodder
Eberhard
E
Max-Volmer-Laboratorium für Biophysikalische Chemie, Technische Universität Berlin, Germany. eberhard.schlodder@tu-berlin.de
Renger
Thomas
T
Raszewski
Grzegorz
G
Coleman
William J
WJ
Nixon
Peter J
PJ
Cohen
Rachel O
RO
Diner
Bruce A
BA
D001426:Bacterial Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D002734:Chlorophyll / Q000737:chemistry / Q000378:metabolism*; D008027:Light; D008958:Models, Molecular; D016297:Mutagenesis, Site-Directed / Q000379:methods; D009154:Mutation; D045332:Photosystem II Protein Complex / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D017433:Protein Structure, Secondary; D046939:Synechocystis / Q000235:genetics / Q000378:metabolism* / Q000528:radiation effects
D001426:Bacterial Proteins; D045332:Photosystem II Protein Complex; D002734:Chlorophyll