title: The X-ray structure of photosystem II reveals a novel electron transport pathway between P680, cytochrome b559 and the energy-quenching cation, ChlZ+.
abstract: When water oxidation by photosystem II (PSII) is impaired, an oxidized chlorophyll (Chl(Z)(+)) is formed that quenches excitation and may prevent photodamage. Both the identification of this Chl(+) and the mechanism of its oxidation and reduction are controversial. Using the available X-ray structures of PSII we calculated the efficiency of two proposed quenchers, Chl(Z)(+)(D1) and Chl(Z)(+)(D2). Of these two, only Chl(Z)(+)(D1) can quench to the degree observed experimentally. We also identify a chain of closely spaced pigments in the structure from Thermosynechococcus vulcanus that we propose to form a novel electron transport pathway between Chl(Z)(D1), beta-carotene, P680(+) and cytochrome b(559).
authors.affiliation: Department of Biological Sciences, Brock University, L2S 3A1, St. Catharines, ON, Canada.
authors.forename: Sergej
authors.initials: S
authors.lastname: Vasil'ev
authors.forename: Gary W
authors.initials: GW
authors.lastname: Brudvig
authors.forename: Doug
authors.initials: D
authors.lastname: Bruce
mesh_terms: D002412:Cations; D002734:Chlorophyll / Q000737:chemistry*; D018360:Crystallography, X-Ray; D000458:Cyanobacteria / Q000737:chemistry / Q000378:metabolism; D003573:Cytochrome b Group / Q000737:chemistry*; D004579:Electron Transport; D007700:Kinetics; D045342:Light-Harvesting Protein Complexes; D008958:Models, Molecular; D010084:Oxidation-Reduction; D045322:Photosynthetic Reaction Center Complex Proteins / Q000737:chemistry* / Q000378:metabolism; D045332:Photosystem II Protein Complex; D010944:Plants / Q000737:chemistry; D019207:beta Carotene / Q000502:physiology
chemical_list: D002412:Cations; D003573:Cytochrome b Group; D045342:Light-Harvesting Protein Complexes; D045322:Photosynthetic Reaction Center Complex Proteins; D045332:Photosystem II Protein Complex; C083100:photosystem II, chlorophyll binding protein, CP-43; D019207:beta Carotene; D002734:Chlorophyll; C025167:P-680; C019313:cytochrome b559