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== Publication Abstract from PubMed ==
== Publication Abstract from PubMed ==
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Crystal structure of photosystem II (PSII) has been reported from prokaryotic cyanobacteria but not from any eukaryotes. In the present study, we improved the purification procedure of PSII dimers from an acidophilic, thermophilic red alga Cyanidium caldarium, and crystallized them in two forms under different crystallization conditions. One had a space group of P222(1) with unit cell constants of a=146.8 A, b=176.9 A, and c=353.7 A, and the other one had a space group of P2(1)2(1)2(1) with unit cell constants of a=209.2 A, b=237.5 A, and c=299.8 A. The unit cell constants of both crystals and the space group of the first-type crystals are different from those of cyanobacterial crystals, which may reflect the structural differences between the red algal and cyanobacterial PSII, as the former contains a fourth extrinsic protein of 20 kDa. X-ray diffraction data were collected and processed to a 3.8 A resolution with the first type crystal. For the second type crystal, a post-crystallization treatment of dehydration was employed to improve the resolution, resulting in a diffraction data of 3.5 A resolution. Analysis of this type of crystal revealed that there are 2 PSII dimers in each asymmetric unit, giving rise to 16 PSII monomers in each unit cell, which contrasts to 4 dimers per unit cell in cyanobacterial crystals. The molecular packing of PSII within the unit cell was constructed with the molecular replacement method and compared with that of the cyanobacterial crystals.
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Photosystem II (PSII) catalyzes light-induced water-splitting, leading to the evolution of molecular oxygen indispensible for life on the earth. The crystal structure of PSII from cyanobacteria has been solved at an atomic level, but the structure of eukaryotic PSII has not been analyzed. Since eukaryotic PSII possesses additional subunits not found in cyanobacterial PSII, it is important to solve the structure of eukaryotic PSII in order to elucidate their detailed functions as well as evolutionary relationships. Here we report the structure of PSII from a red alga Cyanidium caldarium at 2.76 A resolution, which revealed the structure and interaction sites of PsbQ', a unique, 4th extrinsic protein required for stabilizing the oxygen-evolving complex in the lumenal surface of PSII. The PsbQ' subunit was found to be located underneath CP43 in the vicinity of PsbV, and its structure is characterized by a bundle of 4 up-down helices arranged in a similar way to those of cyanobacterial and higher plant PsbQ, although helices I and II of PsbQ' were kinked relative to its higher plant counterpart due to its interactions with CP43. Furthermore, two novel trans-membrane helices were found in the red algal PSII which are not present in cyanobacterial PSII; one of these helices may correspond to PsbW found only in eukaryotic PSII. The present results represent the first crystal structure of PSII from eukaryotic oxygenic organisms, which were discussed in comparison with the structure of cyanobacterial PSII.
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Towards structural elucidation of eukaryotic photosystem II: Purification, crystallization and preliminary X-ray diffraction analysis of photosystem II from a red alga.,Adachi H, Umena Y, Enami I, Henmi T, Kamiya N, Shen JR Biochim Biophys Acta. 2009 Feb;1787(2):121-8. doi: 10.1016/j.bbabio.2008.11.004. , Epub 2008 Nov 19. PMID:19059198<ref>PMID:19059198</ref>
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Novel features of eukaryotic photosystem II revealed by its crystal structure analysis from a red alga.,Ago H, Adachi H, Umena Y, Tashiro T, Kawakami K, Kamiya N, Tian L, Han G, Kuang T, Liu Z, Wang F, Zou H, Enami I, Miyano M, Shen JR J Biol Chem. 2016 Jan 12. pii: jbc.M115.711689. PMID:26757821<ref>PMID:26757821</ref>
From MEDLINE&reg;/PubMed&reg;, a database of the U.S. National Library of Medicine.<br>
From MEDLINE&reg;/PubMed&reg;, a database of the U.S. National Library of Medicine.<br>

Revision as of 07:53, 3 February 2016

Crystal structure of oxygen-evolving photosystem II from a red alga

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