Evolution of oxygen-evolving PSII in view of the extrinsic proteins

光系统II（PSII）在不同的生物体中含有不同的外源蛋白。高等植物的PSII含有33 kDa、23 kDa和17 kDa三种外源蛋白，而蓝藻和红藻的PSII只含有33 kDa蛋白，其余两种蛋白均不存在。相反，两种不同的蛋白质，细胞色素c550和12 kDa的蛋白质，在后者的生物体中被发现。在红藻PSII中还发现了第四种外源蛋白，分子量约为20 kDa，表明在从蓝藻到高等植物的进化过程中，放氧复合体改变了外源蛋白。本研究旨在从外源蛋白的变化来阐明放氧PSII的进化过程。为了达到这一目的，我们计划制备针对红藻PSII的四种外源蛋白的抗体，并利用它们来检测各种生物中的外源蛋白。首先，克隆了编码这四种外源蛋白的基因。克隆的基因在大肠杆菌中成功表达。并制备针对其重组蛋白的抗体。我们已经收集了各种藻类细胞，并计划检查这些藻类细胞对我们构建的抗体的交叉反应性，以澄清哪种生物体包含哪组外源蛋白。

Photosystem II (PSII) contains different extrinsic proteins among different organisms. Higher plant PSII contains the three extrinsic proteins of 33 kDa, 23 kDa and 17 kDa, whereas in cyanobacterial and red algal PSII, only the 33 kDa protein is present but the other two proteins are absent. Instead, two different proteins, cytochrome c550 and 12 kDa protein, were found in the latter organisms. In red algal PSII, a fourth extrinsic protein, a 20 kDa protein, was also found. These facts suggest that the oxygen-evolving complex changed the extrinsic proteins during its evolution from cyanobacteria to higher plants. This study aimed at elucidating the evolutionary process of oxygen-evolving PSII in terms of the changes of the extrinsic proteins. To reach this purpose, we planned to prepare the antibodies against the four extrinsic proteins of red algal PSII and to use them to detect the extrinsic proteins in various organisms. First, the genes encoding the four extrinsic proteins were cloned. Then, the cloned genes were successfully expressed in E.coli. and the antibodies against their recombinant proteins were prepared. We have collected various species of algal cells and are planning to examine the cross-reactivity of these algal cells against the antibodies we constructed, in order to clarify which organism contains which set of the extrinsic proteins.