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首页> 美国卫生研究院文献>The Journal of Biological Chemistry >A Reaction Center-dependent Photoprotection Mechanism in a Highly Robust Photosystem II from an Extremophilic Red Alga Cyanidioschyzon merolae
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A Reaction Center-dependent Photoprotection Mechanism in a Highly Robust Photosystem II from an Extremophilic Red Alga Cyanidioschyzon merolae

机译：从极端嗜热的红藻Cyanidioschyzon merolae高度鲁棒的光系统II中依赖于反应中心的光保护机制。

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摘要

Members of the rhodophytan order Cyanidiales are unique among phototrophs in their ability to live in extremely low pH levels and moderately high temperatures. The photosynthetic apparatus of the red alga Cyanidioschyzon merolae represents an intermediate type between cyanobacteria and higher plants, suggesting that this alga may provide the evolutionary link between prokaryotic and eukaryotic phototrophs. Although we now have a detailed structural model of photosystem II (PSII) from cyanobacteria at an atomic resolution, no corresponding structure of the eukaryotic PSII complex has been published to date. Here we report the isolation and characterization of a highly active and robust dimeric PSII complex from C. merolae. We show that this complex is highly stable across a range of extreme light, temperature, and pH conditions. By measuring fluorescence quenching properties of the isolated C. merolae PSII complex, we provide the first direct evidence of pH-dependent non-photochemical quenching in the red algal PSII reaction center. This type of quenching, together with high zeaxanthin content, appears to underlie photoprotection mechanisms that are efficiently employed by this robust natural water-splitting complex under excess irradiance. In order to provide structural details of this eukaryotic form of PSII, we have employed electron microscopy and single particle analyses to obtain a 17 Å map of the C. merolae PSII dimer in which we locate the position of the protein mass corresponding to the additional extrinsic protein stabilizing the oxygen-evolving complex, PsbQ′. We conclude that this lumenal subunit is present in the vicinity of the CP43 protein, close to the membrane plane.
机译：红藻丹级蓝藻的成员在光养生物中是独一无二的，因为它们能够生活在极低的pH水平和适度的高温下。红藻Cyanidioschyzon merolae的光合作用代表蓝藻和高等植物之间的中间类型，这表明该藻类可能提供原核和真核生物之间的进化联系。尽管我们现在有一个以原子分辨率解​​析的蓝细菌光系统II（PSII）的详细结构模型，但迄今为止，尚未发布真核PSII复合物的相应结构。在这里，我们报告了从C. merolae高活性和强大的二聚体PSII复合物的分离和表征。我们证明了这种复合物在极端的光照，温度和pH条件下具有很高的稳定性。通过测量分离的C. merolae PSII复合物的荧光猝灭特性，我们提供了红色藻类PSII反应中心中pH依赖性非光化学猝灭的第一个直接证据。这种类型的淬灭以及高的玉米黄质含量似乎是光保护机制的基础，该保护机制可在过量辐照下被这种坚固的天然水分解配合物有效利用。为了提供这种PSII真核形式的结构细节，我们采用了电子显微镜和单颗粒分析来获得C. merolae PSII二聚体的17Å图，在其中我们确定了与其他外在蛋白相对应的蛋白质质量位置稳定氧释放复合物PsbQ'的蛋白质。我们得出结论，该腔亚单位存在于CP43蛋白附近，靠近膜平面。

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