Preliminary X-ray diffraction study of crystals of photosystem II from Thermosynechococcus elongates
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CTURE OF MACROMOLECULAR COMPOUNDS
Preliminary Xray Diffraction Study of Crystals of Photosystem II from Thermosynechococcus elongates A. G. Gabdulkhakov and M. V. Dontsova Institute of Protein Research, Russian Academy of Sciences, Institutskaya 4, Pushchino, Moscow region, 142290 Russia email: [email protected] Received June 13, 2013
Abstract—Photosystem II (PSII) is a multicomponent enzyme complex that catalyzes the lightinduced water splitting to molecular oxygen, protons, and electrons. Photosystem II is located in the membranes of cyanobacteria, green algae, and plants. The crystallization of this complex from the thylakoid membranes poses great difficulties. The high sensitivity of photosystem II to light and radiation has an adverse effect on the crystal quality, as well as on the quality of Xray diffraction data. This is the reason why the crystal struc ture of PSII from Thermosynechococcus elongates has as yet not been determined at high resolution. The opti mization of the strategy for collecting Xray diffraction data from PSII crystals has resulted in an increase in the resolution to 2.75 Å, which made it possible to determine the positions of ions and some water molecules playing an important role in the functioning of PSII. DOI: 10.1134/S1063774514010040
INTRODUCTION
us to obtain Xray data from PSII crystals at 2.75 Å resolution. The refinement of the threedimensional structure of PSII is currently underway.
Oxygen, which is a byproduct of photosynthesis, is necessary to sustain human life. The general state of human health depends to a large extent on the oxygen level in the atmosphere. In addition, free oxygen forms the ozone layer protecting life on the earth from UV radiation. It took about several billion years for photo synthetic organisms to build up the oxygen content in the atmosphere to its present level. In nature, the lightinduced formation of oxygen from water is catalyzed by an enzyme called photosys tem II (PSII). The threedimensional structure of PSII has been studied in past decades. It was found that PSII is a complex comprising proteins and lipids that bind chlorophylls and other pigments. The unique Mn4CaO5 cluster serves as the catalytic site of PSII, where the photooxidation of water takes place. Although the spatial arrangement of proteins, lipids, and pigments in PSII has been studied in sufficient detail, this enzyme continues to attract particular interest. The mechanism of the photosynthetic reac tion, as well as the mechanisms of the entry of sub strates and the release of products of the reactions that occur within this multicomponent protein–pigment complex, remain unknown. Hence, the investigation of the threedimensional structure of PSII at atomic resolution and the analysis of interactions of PSII with small molecules and ions is a topical problem. In the present study, we briefly describe the isola tion, purification, and crystallization of PSII from the cyanobacterium Thermosynechococcus elongates (T. elongates). Strategy for collecting Xray di
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