Heredia P, De Las Rivas J
Instituto de Recursos Naturales y Agrobiología (CSIC), P.O. Box 257, 37071 Salamanca, Spain.
Biochemistry. 2003 Oct 14;42(40):11831-8. doi: 10.1021/bi034582j.
The structure and function of the photosystem II PsbO extrinsic protein is under intense research, being an essential part of the biomolecular engine that carries out water oxidation and oxygen production. This paper presents a structural analysis of the isolated PsbO protein by FTIR spectroscopy, reporting detailed secondary structure quantification and changes in the secondary structure content of the protein attributed to the effect of calcium (Ca(2+)). Measurements in H(2)O and D(2)O have allowed us to see the effect of calcium on the conformation of the protein. The results indicate that (i) the protein presents a major content of beta-structure (i.e., beta-sheet, beta-strands, beta-turns) as detected by the infrared bands at 1624-1625, 1678-1679, 1688-1689 cm(-1), which account for about 38% in water and 33% in heavy water, in the presence of calcium; and (ii) the amount of this beta-structure fraction increases 7-10% in the absence of calcium, with a concomitant decrease in loops and nonordered structure. The thermal denaturation profile of the protein in the presence of calcium showed low stability with T(m) approximately 56 degrees C. This profile also shows a second phase of denaturation above 60 degrees C and the appearance of aggregation signals above 70 degrees C. Our observations indicate that calcium is able to modify the conformation of the protein at least in solution and confirm that PsbO is mainly a beta-protein where beta-sheet is the major ordered secondary structure element of the protein core.
光系统II的PsbO外在蛋白的结构与功能是深入研究的对象，它是进行水氧化和氧气生成的生物分子引擎的重要组成部分。本文通过傅里叶变换红外光谱法对分离出的PsbO蛋白进行了结构分析，报告了详细的二级结构定量以及归因于钙（Ca(2+)）作用的蛋白质二级结构含量变化。在H(2)O和D(2)O中的测量使我们能够观察到钙对蛋白质构象的影响。结果表明：（i）如在1624 - 1625、1678 - 1679、1688 - 1689 cm(-1)处的红外波段所检测到的，该蛋白质呈现出主要的β-结构含量（即β-折叠、β-链、β-转角），在有钙存在的情况下，在水中约占38%，在重水中约占33%；（ii）在没有钙的情况下，这种β-结构部分的含量增加7 - 10%，同时环和无序结构减少。有钙存在时蛋白质的热变性曲线显示稳定性较低，T(m)约为56℃。该曲线还显示在60℃以上有第二个变性阶段，在70℃以上出现聚集信号。我们的观察表明钙至少在溶液中能够改变蛋白质的构象，并证实PsbO主要是一种β-蛋白，其中β-折叠是蛋白质核心的主要有序二级结构元件。
