光系统放氧复合物II的S2-to-S3态转变热力学
Thermodynamics of the S2-to-S3 State Transition of the Oxygen-Evolving Complex of Photosystem II
摘要：
室温泵浦-探测X射线自由电子激光（XFEL）测量用于串行飞秒晶体学提供了显着的信息的光系统II的氧析出反应的催化（S-状态）中间体的结构。然而，这些中间体的混合群体和中等分辨率限制了对当前实验数据的解释。S3 XFEL结构在OEC附近显示出额外的密度，其可能对应于水/氢氧化物分子。然而，在最新的结构中，这个额外的氧距离D1-E189的Oe 2为2.08 μ m，这比两个氧的范德华半径之和更接近。在这里，我们使用玻尔兹曼统计和蒙特卡罗采样提供了一个模型的S2到S3状态转换，允许结构变化和插入额外的水/氢氧化物。根据我们的模型，水/氢氧化物除了放氧复合物（OEC）是不符合化学条件的有利S2 g = 2状态，但它是在S2 g = 4.1氧化还原异构体。因此，S3态的形成开始于从S2 g = 2到S2 g = 4.1结构的转变。然后，静电相互作用支持D1-H190的质子化和Ca 2+连接的水（W3）的去质子化，质子损失到管腔。W3氢氧化物向Mn 4移动，完成Mn 4的配位壳层，并在S3状态下氧化为Mn（IV）。此外，将额外的氢氧化物结合到Mn 1导致D1-E189在S2 g = 4.1和S3结构中的构象变化。在S3状态中质子化的D1-E189的数量增加。
英文摘要：
The room temperature pump-probe X-ray free electron laser (XFEL) measurements used for serial femtosecond crystallography provide remarkable information about the structures of the catalytic (S-state) intermediates of the oxygen-evolution reaction of photosystem II. However, mixed populations of these intermediates and moderate resolution limit the interpretation of the data from current experiments. The S3 XFEL structures show extra density near the OEC that may correspond to a water/hydroxide molecule. However, in the latest structure, this additional oxygen is 2.08 Å from the Oe2 of D1-E189, which is closer than the sum of the van der Waals radii of the two oxygens. Here, we use Boltzmann statistics and Monte Carlo sampling to provide a model for the S2-to-S3 state transition, allowing structural changes and the insertion of an additional water/hydroxide. Based on our model, water/hydroxide addition to the oxygen-evolving complex (OEC) is not thermodynamically favorable in the S2 g = 2 state, but it is in the S2 g = 4.1 redox isomer. Thus, formation of the S3 state starts by a transition from the S2 g = 2 to the S2 g = 4.1 structure. Then, electrostatic interactions support protonation of D1-H190 and deprotonation of the Ca2+-ligated water (W3) with proton loss to the lumen. The W3 hydroxide moves toward Mn4, completing the coordination shell of Mn4 and moving with its oxidation to Mn(IV) in the S3 state. In addition, binding additional hydroxide to Mn1 leads to a conformational change of D1-E189 in the S2 g = 4.1 and S3 structures. In the S3 state in the population of protonated D1-E189 increases.
机构、总结、中文摘要均由AI分析而来，可能存在错误，请以论文正文为准。
