Department of Life Sciences (Biology), Graduate School of Art and Sciences, University of Tokyo, Komaba, Meguro, Tokyo 153-8902, Japan.
J Biol Chem. 2010 Sep 17;285(38):29191-9. doi: 10.1074/jbc.M110.146092. Epub 2010 Jul 14.
Oxygen-evolving photosystem II (PSII) isolated from a marine centric diatom, Chaetoceros gracilis, contains a novel extrinsic protein (Psb31) in addition to four red algal type extrinsic proteins of PsbO, PsbQ', PsbV, and PsbU. In this study, the five extrinsic proteins were purified from alkaline Tris extracts of the diatom PSII by anion and cation exchange chromatographic columns at different pH values. Reconstitution experiments in various combinations with the purified extrinsic proteins showed that PsbO, PsbQ', and Psb31 rebound directly to PSII in the absence of other extrinsic proteins, indicating that these extrinsic proteins have their own binding sites in PSII intrinsic proteins. On the other hand, PsbV and PsbU scarcely rebound to PSII alone, and their effective bindings required the presence of all of the other extrinsic proteins. Interestingly, PSII reconstituted with Psb31 alone considerably restored the oxygen evolving activity in the absence of PsbO, indicating that Psb31 serves as a substitute in part for PsbO in supporting oxygen evolution. A significant difference found between PSIIs reconstituted with Psb31 and with PsbO is that the oxygen evolving activity of the former is scarcely stimulated by Cl(-) and Ca(2+) ions but that of the latter is largely stimulated by these ions, although rebinding of PsbV and PsbU activated oxygen evolution in the absence of Cl(-) and Ca(2+) ions in both the former and latter PSIIs. Based on these results, we proposed a model for the association of the five extrinsic proteins with intrinsic proteins in diatom PSII and compared it with those in PSIIs from the other organisms.
从海洋中心硅藻 Chaetoceros gracilis 中分离出的产氧光合系统 II（PSII）除了含有四个红藻型的 PsbO、PsbQ'、PsbV 和 PsbU 外，还含有一种新型的外显子蛋白（Psb31）。在这项研究中，通过在不同 pH 值下使用阴离子和阳离子交换色谱柱从硅藻 PSII 的碱性 Tris 提取物中纯化了这五种外显子蛋白。用纯化的外显子蛋白进行的各种组合的重建实验表明，PsbO、PsbQ'和 Psb31 在没有其他外显子蛋白的情况下直接与 PSII 重新结合，表明这些外显子蛋白在 PSII 内在蛋白中有自己的结合位点。另一方面，PsbV 和 PsbU 单独很少与 PSII 重新结合，它们的有效结合需要存在所有其他外显子蛋白。有趣的是，单独用 Psb31 重建的 PSII 在没有 PsbO 的情况下相当大地恢复了氧气产生活性，表明 Psb31 在部分支持氧气产生方面替代了 PsbO。在用 Psb31 和 PsbO 重建的 PSII 之间发现了一个显著的区别，即前者的氧气产生活性几乎不受 Cl(-)和 Ca(2+)离子的刺激，而后者的氧气产生活性在很大程度上受到这些离子的刺激，尽管在没有 Cl(-)和 Ca(2+)离子的情况下，PsbV 和 PsbU 的重新结合都激活了两种 PSII 中的氧气产生。基于这些结果，我们提出了一种硅藻 PSII 中外显子蛋白与内在蛋白结合的模型，并将其与其他生物体的 PSII 进行了比较。
