title: Site-directed mutations at D1-His198 and D1-Thr179 of photosystem II in Synechocystis sp. PCC 6803: deciphering the spectral properties of the PSII reaction centre.
abstract: Site-directed mutations were constructed in photosystem II of Synechocystis sp. PCC6803 in which the axial ligand, D1-His198, of special pair chlorophyll PD1 was replaced with Gln and where D1-Thr179, which overlies monomeric chlorophyll ChlD1, was replaced with His. The D1-His198Gln mutation produces a 3nm displacement to the blue of the bleaching minimum in the Soret and in the Qy region of the (P+QA--PQA) absorbance difference spectrum. To a first approximation, the bleaching can be assigned to the low-energy exciton transition of the special pair chlorophylls PD1/PD2. The D1-Thr179His mutation produces a 2nm displacement to the red of the bleaching minimum in the Qy region of the (3P-1P) absorbance difference spectrum. Analysis of the flash-induced (P+QA--PQA) and (3P-1P) absorbance difference spectra of both mutants compared with wild-type at 80K indicate that the cation of the oxidized donor P+ is predominantly localized on the chlorophyll PD1 of the special pair and that the reaction centre triplet state, produced upon charge recombination from 3[P+Pheo-], when the primary quinone electron acceptor QA is doubly reduced, is primarily localized on ChlD1.
authors.affiliation: Max-Volmer-Laboratorium für Biophysikalische Chemie, Technische Universität Berlin, Strasse des 17. Juni 135, 10623 Berlin, Germany. eberhard.schlodder@tu-berlin.de
authors.forename: Eberhard
authors.initials: E
authors.lastname: Schlodder
authors.forename: William J
authors.initials: WJ
authors.lastname: Coleman
authors.forename: Peter J
authors.initials: PJ
authors.lastname: Nixon
authors.forename: Rachel O
authors.initials: RO
authors.lastname: Cohen
authors.forename: Thomas
authors.initials: T
authors.lastname: Renger
authors.forename: Bruce A
authors.initials: BA
authors.lastname: Diner
mesh_terms: D004269:DNA, Bacterial / Q000737:chemistry / Q000235:genetics; D008958:Models, Molecular; D016297:Mutagenesis, Site-Directed; D045322:Photosynthetic Reaction Center Complex Proteins / Q000737:chemistry* / Q000235:genetics; D045332:Photosystem II Protein Complex / Q000737:chemistry* / Q000235:genetics; D013057:Spectrum Analysis; D046940:Synechococcus / Q000737:chemistry* / Q000235:genetics
chemical_list: D004269:DNA, Bacterial; D045322:Photosynthetic Reaction Center Complex Proteins; D045332:Photosystem II Protein Complex