Photosystem I at 4 A resolution represents the first structural model of a joint photosynthetic reaction centre and core antenna system.
The 4 A X-ray structure model of trimeric photosystem I of the cyanobacterium Synechococcus elongatus reveals 31 transmembrane, nine surface and three stromal alpha-helices per monomer, assigned to the 11 protein subunits: PsaA and PsaB are related by a pseudo two-fold axis normal to the membrane plane, along which the electron transfer pigments are arranged. 65 antenna chlorophyll a (Chl a) molecules separated by < or = 16 A form an oval, clustered net continuous with the electron transfer chain through the second and third Chl a pairs of the electron transfer system. This suggests a dual role for these Chl a both in excitation energy and electron transfer. The architecture of the protein core indicates quinone and iron-sulphur type reaction centres to have a common ancestor.
Institut für Kristallographie, Freie Universität Berlin, Germany.
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Krauss
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Schubert
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O
Klukas
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Fromme
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Witt
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Saenger
D002462:Cell Membrane / Q000737:chemistry; D002734:Chlorophyll / Q000737:chemistry*; D000077194:Chlorophyll A; D000458:Cyanobacteria / Q000737:chemistry*; D004579:Electron Transport; D008958:Models, Molecular; D015394:Molecular Structure; D045322:Photosynthetic Reaction Center Complex Proteins / Q000737:chemistry*; D017433:Protein Structure, Secondary
D045322:Photosynthetic Reaction Center Complex Proteins; D002734:Chlorophyll; D000077194:Chlorophyll A