Wang Jimin
Department of Molecular Biophysics and Biochemistry, Yale University, New Haven, CT 06520-8114, USA.
Acta Crystallogr D Struct Biol. 2024 Dec 1;80(Pt 12):850-861. doi: 10.1107/S2059798324011392. Epub 2024 Nov 28.
Recently, the conclusions drawn from crystallographic data about the number of oxygen ligands associated with the CaMn cofactor in the oxygen-evolving center (OEC) of Thermosynechococcus vulcanus photosystem II (PSII) have been called into question. Here, using OEC-omit, metal ion-omit and ligand-omit electron-density maps, it is shown that the number of oxygen ligands ranges from three in the functional OEC of monomer B following dark adaption (0F), i.e. in its ground state (PDB entry 6jlj/0F and PDB entry 6jlm/0F), to five for both monomers of PSII in photo-advanced states following exposure to one and two flashes of light. For a significant fraction of the 0F OECs in monomer A, the number is four (PDB entry 6jlj/0F). Following one flash it increases to five (PDB entry 6jlk/1F), where it remains after a second flash (PDB entry 6jlj/2F). Following a third flash (3F), it decreases to three (PDB entry 6jlp/3F), suggesting that an O molecule has been produced. These observations suggest a mechanism for the reaction that transforms the O atoms of the water molecules bound at the O3 and O1 sites of the OEC into O.
最近，从晶体学数据得出的关于嗜热栖热放线菌光系统II（PSII）放氧中心（OEC）中与CaMn辅因子相关的氧配体数量的结论受到了质疑。在这里，使用省略OEC、省略金属离子和省略配体的电子密度图表明，氧配体的数量范围从暗适应后（0F）单体B的功能性OEC中的三个，即其基态（PDB条目6jlj/0F和PDB条目6jlm/0F），到暴露于一次和两次闪光后的光激发状态下PSII的两个单体中的五个。对于单体A中相当一部分0F OEC，数量为四个（PDB条目6jlj/0F）。一次闪光后增加到五个（PDB条目6jlk/1F），第二次闪光后保持在该数量（PDB条目6jlj/2F）。第三次闪光（3F）后，它减少到三个（PDB条目6jlp/3F），这表明产生了一个O分子。这些观察结果提出了一种将结合在OEC的O3和O1位点的水分子的O原子转化为O的反应机制。
