Functional roles of D2-Lys317 and the interacting chloride ion in the water oxidation reaction of photosystem II as revealed by fourier transform infrared analysis.
Functional roles of D2-Lys317 and the interacting chloride ion in the water oxidation reaction of photosystem II as revealed by fourier transform infrared analysis.
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DOI：
10.1021/bi301699h
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发表时间：
2013-07-16
期刊：
影响因子：
2.9
通讯作者：
Noguchi T
中科院分区：
文献类型：
--
作者：
Suzuki H;Yu J;Kobayashi T;Nakanishi H;Nixon PJ;Noguchi T
光合作用水氧化在植物和蓝藻催化的Mn 4CaO 5集群内的光系统II（PSII）的蛋白质复合物。两个Cl-离子绑定附近的Mn 4CaO 5簇作为不可缺少的辅助因子，但其功能作用仍有待澄清。我们通过对集胞藻PCC 6803的D2-K317 R突变体进行傅里叶变换红外光谱（FTIR）分析，结合Cl-/NO3-替代，研究了Cl-离子与D2-K317（指定为Cl-1）相互作用的作用。D2-K317 R突变干扰了S1 → S2跃迁时FTIR差谱中COO-伸缩振动和主链酰胺振动区域的谱带。此外，这种突变改变了NO3-处理PSII光谱中的15 N同位素编辑的NO3-带。这些结果提供了第一个实验证据，Cl-1位与Mn_4CaO_5团簇耦合，其相互作用受到S_1 → S_2跃迁的影响。结果还表明，在1748 cm-1处由COOH基团产生的负带被D2-K317 R突变以及NO3-处理改变为正强度，这表明Cl-1位点影响在共同的氢键网络中Mn 4CaO 5簇附近的COOH/COO-基团的pKa。结合D2-K317 R的核心复合物在适度脱水后S3 → S 0转变效率显著降低的观察结果，表明D2-K317和Cl-1参与了从Mn 4CaO 5簇到内腔的质子转移途径，该途径在S3 → S 0转变中起作用。
Photosynthetic water oxidation in plants and cyanobacteria is catalyzed by a Mn4CaO5 cluster within the photosystem II (PSII) protein complex. Two Cl– ions bound near the Mn4CaO5 cluster act as indispensable cofactors, but their functional roles remain to be clarified. We have investigated the role of the Cl– ion interacting with D2-K317 (designated Cl-1) by Fourier transform infrared spectroscopy (FTIR) analysis of the D2-K317R mutant of Synechocystis sp. PCC 6803 in combination with Cl–/NO3– replacement. The D2-K317R mutation perturbed the bands in the regions of the COO– stretching and backbone amide vibrations in the FTIR difference spectrum upon the S1 → S2 transition. In addition, this mutation altered the 15N isotope-edited NO3– bands in the spectrum of NO3–-treated PSII. These results provide the first experimental evidence that the Cl-1 site is coupled with the Mn4CaO5 cluster and its interaction is affected by the S1 → S2 transition. It was also shown that a negative band at 1748 cm–1 arising from COOH group(s) was altered to a positive intensity by the D2-K317R mutation as well as by NO3– treatment, suggesting that the Cl-1 site affects the pKa of COOH/COO– group(s) near the Mn4CaO5 cluster in a common hydrogen bond network. Together with the observation that the efficiency of the S3 → S0 transition significantly decreased in the core complexes of D2-K317R upon moderate dehydration, it is suggested that D2-K317 and Cl-1 are involved in a proton transfer pathway from the Mn4CaO5 cluster to the lumen, which functions in the S3 → S0 transition.
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