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
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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DOI：
10.1074/jbc.m117.815183
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发表时间：
2017-12-08
影响因子：
4.8
通讯作者：
Noguchi, Takumi
中科院分区：
文献类型：
--
作者：
Nagao, Ryo;Ueoka-Nakanishi, Hanayo;Noguchi, Takumi
在光合水氧化过程中，两个水分子在光系统II（PSII）的Mn 4CaO 5簇中通过S态循环转化为一个氧分子和四个质子。从催化位点到内腔的有效质子出口对于该过程是必不可少的。然而，个别质子通过PSII蛋白的出口途径仍有待确定。在这项研究中，我们研究了参与的氢键网络附近的氧化还原活性酪氨酸Y-Z在质子转移过程中的S-状态循环。我们重点关注D1-Asn-298定点变体的光谱分析，D1-Asn-298是一种参与Y-Z附近氢键网络的残基。我们发现集胞藻PCC 6803的D1-N298 A突变体表现出的O-2进化活性约为野生型的10%。D1-N298 A和野生型D1在Y-Z氧化过程中具有非常相似的热释光发光曲线和FTIR差谱特征，表明取代对Y-Z的氢键结构和Mn 4CaO 5团簇向Y-Z的电子转移影响很小。然而，在D1-N298 A突变体中，延迟发光的闪光数依赖性表现出单调增加而没有振荡，并且S-态循环的FTIR差谱分别表明S-2 S-3和S-3 S-0跃迁的部分和显著抑制。这些结果表明，D1-N298 A取代抑制了S-2 S-3和S-3 S-0跃迁中的质子转移过程。这反过来表明，氢键网络附近的Y-Z可以作为一个质子转移途径在光合水氧化的功能。
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 Y-Z 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 Y-Z. We found that the D1-N298A mutant of Synechocystis sp. PCC 6803 exhibits an O-2 evolution activity of approximate to 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 Y-Z oxidation, suggesting that the hydrogen-bonded structure of Y-Z and electron transfer from the Mn4CaO5 cluster to Y-Z 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 S-2 S-3 and S-3 S-0 transitions, respectively. These results suggest that the D1-N298A substitution inhibits the proton transfer processes in the S-2 S-3 and S-3 S-0 transitions. This in turn indicates that the hydrogen-bond network near Y-Z can be functional as a proton transfer pathway during photosynthetic water oxidation.