Photosystem II at 3.0 Å Resolution


Photosynthesis is one of the most fundamental and important natural processes. Responsible for the maintenance of the oxygen level in the atmosphere and the reduction of CO2 to carbohydrates, a detailed understanding of photosynthesis has been developed following decades of careful investigations. A complete picture of the process requires the synthesis of the information from many physical and bio-physical techniques, in addition to the three dimensional structures of the proteins involved.

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In plants, algae and cyanobacteria, photosynthesis is initiated at photosystem II (PSII), a large membrane-intrinsic homodimeric protein-cofactor complex. By capturing sunlight, PSII produces the energy required to power the oxidation of water to atmospheric oxygen. Researchers from the Freie Universität and Technische Universität of Berlin have recently been able to present the most detailed model of PSII currently available. A complex of 20 protein sub-units and 77 co-factors was revealed in near atomic detail. It seems that a high degree of flexibility is required for the protein function and that this flexibility is "lubricated" by a number of organised lipid molecules. By an appreciation of the spatial arrangement of the -carotenes and metal centres contained within PSII it was possible to further our understanding concerning the electron (and energy) transfer mechanisms required to facilitate the transfer of redox products through the components of the photosynthetic pathway.

Two views of PSII isolated from the cyanobacterium Synechococcus elongatus.

Fig. 1: Two views of PSII isolated from the cyanobacterium Synechococcus elongatus. (a) view along the membrane plane, the pseudo-twofold axis relating the monomers in the homodimer is indicated. The principal protein subunits (reaction center D1, D2; antennae subunits CP43, CP47; Cyt b-559 and membrane-extrinsic subunits) in different colours and small subunits with unknown function in grey. Cofactors are indicated, chlorophylls (green), ß-carotenes (orange), lipids (black), haems (blue), Mn4Ca cluster (red spheres). (b) view from the "top" side on the membrane plane, colours and labelling (in one monomer) as in (a).


Principal Publication and Authors
B. Loll (a,b), J. Kern (c), W. Saenger (a), A. Zouni (c) and J. Biesiadka (a), Nature 438, 1040-1044 (2005).
(a) Institut für Chemie und Biochemie/Kristallographie, Freie Universität Berlin (Germany)
(b) Present address: Max-Planck-Institut für Medizinische Forschung, Abteilung für Biomolekulare Mechanismen, Heidelberg (Germany)
(c) Institut für Chemie/Max Volmer Laboratorium für Biophysikalische Chemie, Technische Universität Berlin (Germany)