Photosystem II (PSII) is a multisubunit enzyme embedded in the lipid environment of the thylakoid membranes of plants, algae and cyanobacteria. Powered by light, this enzyme catalyses the chemically and thermodynamically demanding reaction of water splitting. In so doing, it releases dioxygen into the atmosphere and provides the reducing equivalents required for the conversion of CO2 into the organic molecules of life. Recently, a fully refined structure of a 700 kDa cyanobacterial dimeric PSII complex was elucidated by X-ray crystallography which gave organizational and structural details of the 19 subunits (16 intrinsic and three extrinsic) which make up each monomer and provided information about the position and protein environments of 57 different cofactors. The water-splitting site was revealed as a cluster of four Mn ions and a Ca2+ ion surrounded by amino acid side chains, of which six or seven form direct ligands to the metals. The metal cluster was modelled as a cubane-like structure composed of three Mn ions and the Ca2+ linked by oxo-bonds with the fourth Mn attached to the cubane via one of its oxygens. The overall structure of the catalytic site is providing a framework to develop a mechanistic scheme for the water-splitting process, knowledge which could have significant implications for mimicking the reaction in an artificial chemical system.
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October 2006
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October 25 2006
Photosystem II: an enzyme of global significance
J. Barber
J. Barber
1
1Division of Molecular Biosciences, Faculty of Natural Sciences, Imperial College London, London SW7 2AZ, U.K.
1email j.barber@imperial.ac.uk
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Publisher: Portland Press Ltd
Received:
June 21 2006
Online ISSN: 1470-8752
Print ISSN: 0300-5127
© 2006 The Biochemical Society
2006
Biochem Soc Trans (2006) 34 (5): 619–631.
Article history
Received:
June 21 2006
Citation
J. Barber; Photosystem II: an enzyme of global significance. Biochem Soc Trans 1 October 2006; 34 (5): 619–631. doi: https://doi.org/10.1042/BST0340619
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