Department of Chemistry , Yale University , New Haven , Connecticut 06520-8107 , United States.
Department of Biochemistry , University of California , Riverside , California 92521 , United States.
Biochemistry. 2019 Mar 12;58(10):1379-1387. doi: 10.1021/acs.biochem.8b01184. Epub 2019 Feb 15.
In photosystem II (PSII), photosynthetic water oxidation occurs at the tetramanganese-calcium cluster that cycles through light-induced intermediates (S-S) to produce oxygen from two substrate waters. The surrounding hydrogen-bonded amino acid residues and waters form channels that facilitate proton transfer and substrate water delivery, thereby ensuring efficient water oxidation. The residue D1-S169 lies in the "narrow" channel and forms hydrogen bonds with the MnCaO cluster via waters W1 and Wx. To probe the role of the narrow channel in substrate-water binding, we studied the D1-S169A mutation. PSII core complexes isolated from mutant cells exhibit inefficient S-state cycling and delayed oxygen evolution. The S-state multiline EPR spectrum of D1-S169A PSII core complexes differed significantly from that of wild-type, and FTIR difference spectra showed that the mutation strongly perturbs the extensive network of hydrogen bonds that extends at least from D1-Y161 (Y) to D1-D61. These results imply a possible role of D1-S169 in proton egress or substrate water delivery.
在光系统 II（PSII）中，光合作用的水氧化发生在四锰-钙簇上，该簇通过光诱导中间体（S-S）循环，从两个基质水中产生氧气。周围的氢键氨基酸残基和水形成通道，促进质子转移和基质水的输送，从而确保有效的水氧化。残基 D1-S169 位于“狭窄”通道中，并通过水 W1 和 Wx 与 MnCaO 簇形成氢键。为了探究窄通道在基质水结合中的作用，我们研究了 D1-S169A 突变。从突变细胞中分离出的 PSII 核心复合物表现出低效的 S 态循环和延迟的氧气释放。D1-S169A PSII 核心复合物的 S 态多线 EPR 光谱与野生型明显不同，FTIR 差谱表明该突变强烈干扰了从 D1-Y161（Y）到 D1-D61 的广泛氢键网络。这些结果表明 D1-S169 可能在质子逸出或基质水输送中发挥作用。
