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首页> 外文期刊>Proceedings of the National Academy of Sciences of the United States of America >A hydrogen-bonding network plays a catalytic role in photosynthetic oxygen evolution
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A hydrogen-bonding network plays a catalytic role in photosynthetic oxygen evolution

机译：氢键网络在光合作用的氧气释放中起催化作用

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In photosystem II, oxygen evolution occurs by the accumulation of photo-induced oxidizing equivalents at the oxygen-evolving complex (OEC). The sequentially oxidized states are called the S0-S4 states, and the dark stable state is Sv Hydrogen bonds to water form a network around the OEC; this network is predicted to involve multiple peptide carbonyl groups. In this work, we tested the idea that a network of hydrogen bonded water molecules plays a catalytic role in water oxidation. As probes, we used OEC peptide carbonyl frequencies, the substrate-based inhibitor, ammonia, and the sugar, trehalose. Reaction-induced FT-IR spectroscopy was used to describe the protein dynamics associated with the S1 to S2 transition. A shift in an amide CO vibrational frequency (1664 (S1) to 1653 (S2) cm~1) was observed, consistent with an increase in hydrogen bond strength when the OEC is oxidized. Treatment with ammonia/ammonium altered these CO vibrational frequencies. The ammonia-induced spectral changes are attributed to alterations in hydrogen bonding, when ammonia/ammonium is incorporated into the OEC hydrogen bond network. The ammonia-induced changes in CO frequency were reversed or blocked when trehalose was substituted for sucrose. This trehalose effect is attributed to a displacement of ammonia molecules from the hydrogen bond network. These results imply that ammonia, and by extension water, participate in a catalytically essential hydrogen bond network, which involves OEC peptide CO groups. Comparison to the ammonia transporter, AmtB, reveals structural similarities with the bound water network in the OEC.
机译：在光系统II中，氧气的释放是通过在氧气释放复合物（OEC）处积累光诱导的氧化当量而发生的。依次被氧化的状态称为S0-S4状态，黑暗的稳定状态为Sv氢键与水形成OEC周围的网络。预计该网络涉及多个肽羰基。在这项工作中，我们测试了氢键水分子网络在水氧化中起催化作用的想法。作为探针，我们使用了OEC肽的羰基频率，基于底物的抑制剂氨和糖，海藻糖。反应诱导的FT-IR光谱用于描述与S1到S2跃迁相关的蛋白质动力学。观察到酰胺CO振动频率的变化（从1664（S1）到1653（S2）cm〜1），这与OEC氧化时氢键强度的增加一致。用氨/铵处理改变了这些CO振动频率。当氨/铵结合到OEC氢键网络中时，氨引起的光谱变化归因于氢键的变化。用海藻糖代替蔗糖时，氨诱导的CO频率变化被逆转或阻止。该海藻糖效应归因于氨分子从氢键网络中的置换。这些结果暗示氨，以及通过延伸的水，参与催化必需的氢键网络，该氢键网络涉及OEC肽CO基团。与氨转运体AmtB的比较揭示了与OEC中束缚水网络的结构相似性。

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