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首页> 美国卫生研究院文献>The Journal of Biological Chemistry >D1-Asn-298 in photosystem II is involved in a hydrogen-bond network near the redox-active tyrosine YZ for proton exit during water oxidation
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D1-Asn-298 in photosystem II is involved in a hydrogen-bond network near the redox-active tyrosine YZ for proton exit during water oxidation

机译：光系统II中的D1-Asn-298参与了氧化还原活性酪氨酸YZ附近的氢键网络在水氧化过程中质子逸出

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摘要

In photosynthetic water oxidation, two water molecules are converted into one oxygen molecule and four protons at the Mn4CaO5 cluster in photosystem II (PSII) via the S-state cycle. Efficient proton exit from the catalytic site to the lumen is essential for this process. However, the exit pathways of individual protons through the PSII proteins remain to be identified. In this study, we examined the involvement of a hydrogen-bond network near the redox-active tyrosine YZ in proton transfer during the S-state cycle. We focused on spectroscopic analyses of a site-directed variant of D1-Asn-298, a residue involved in a hydrogen-bond network near YZ. We found that the D1-N298A mutant of Synechocystis sp. PCC 6803 exhibits an O2 evolution activity of ∼10% of the wild-type. D1-N298A and the wild-type D1 had very similar features of thermoluminescence glow curves and of an FTIR difference spectrum upon YZ oxidation, suggesting that the hydrogen-bonded structure of YZ and electron transfer from the Mn4CaO5 cluster to YZ were little affected by substitution. In the D1-N298A mutant, however, the flash-number dependence of delayed luminescence showed a monotonic increase without oscillation, and FTIR difference spectra of the S-state cycle indicated partial and significant inhibition of the S2 → S3 and S3 → S0 transitions, respectively. These results suggest that the D1-N298A substitution inhibits the proton transfer processes in the S2 → S3 and S3 → S0 transitions. This in turn indicates that the hydrogen-bond network near YZ can be functional as a proton transfer pathway during photosynthetic water oxidation.
机译：在光合水氧化中，两个水分子通过S状态循环在光系统II（PSII）中的Mn4CaO5簇上转换为一个氧分子和四个质子。质子从催化部位到管腔的有效出口对于该过程至关重要。但是，各个质子通过PSII蛋白的出口途径仍有待确定。在这项研究中，我们研究了S状态循环中质子转移过程中，氧化还原活性酪氨酸YZ附近的氢键网络的参与。我们专注于D1-Asn-298的定点变异体的光谱分析，D1-Asn-298是YZ附近氢键网络中的一个残基。我们发现D1-N298A突变体的Synechocystis sp。 PCC 6803的O2释放活性约为野生型的10％。 D1-N298A和野生型D1具有非常相似的热致发光辉光曲线和YZ氧化后的FTIR差异光谱的特征，表明YZ的氢键结构和电子从Mn4CaO5团簇向YZ的转移几乎不受取代的影响。然而，在D1-N298A突变体中，延迟发光的闪烁次数依赖性显示出单调增加而没有振荡，并且S状态循环的FTIR差异光谱表明，S2→S3和S3→S0过渡受到部分和明显的抑制，分别。这些结果表明，D1-N298A取代抑制了S2→S3和S 3 →S 0 跃迁中的质子转移过程。这又表明，Y Z 附近的氢键网络可以在光合水氧化过程中充当质子传递途径。

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