Zahariou Georgia, Ioannidis Nikolaos, Sanakis Yiannis, Pantazis Dimitrios A
Institute of Nanoscience & Nanotechnology, NCSR "Demokritos", Athens, 15310, Greece.
Max-Planck-Institut für Kohlenforschung, Kaiser-Wilhelm-Platz 1, 45470, Mülheim an der Ruhr, Germany.
Angew Chem Int Ed Engl. 2021 Feb 8;60(6):3156-3162. doi: 10.1002/anie.202012304. Epub 2020 Dec 10.
Among the intermediate catalytic steps of the water-oxidizing Mn CaO cluster of photosystem II (PSII), the final metastable S state is critically important because it binds one substrate and precedes O evolution. Herein, we combine X- and Q-band EPR experiments on native and methanol-treated PSII of Spinacia oleracea and show that methanol-treated PSII preparations of the S state correspond to a previously uncharacterized high-spin (S=6) species. This is confirmed as a major component also in intact photosynthetic membranes, coexisting with the previously known intermediate-spin conformation (S=3). The high-spin intermediate is assigned to a water-unbound form, with a Mn subunit interacting ferromagnetically via anisotropic exchange with a coordinatively unsaturated Mn ion. These results resolve and define the structural heterogeneity of the S state, providing constraints on the S to S transition, on substrate identity and delivery pathways, and on the mechanism of O-O bond formation.
在光系统II（PSII）的水氧化锰钙簇的中间催化步骤中，最终的亚稳态S态至关重要，因为它结合一种底物并先于氧气生成。在此，我们结合对菠菜天然和甲醇处理的PSII进行的X波段和Q波段电子顺磁共振实验，结果表明，甲醇处理的PSII的S态制剂对应于一种先前未表征的高自旋（S = 6）物种。这也被确认为完整光合膜中的主要成分，与先前已知的中间自旋构象（S = 3）共存。高自旋中间体被认为是一种水未结合形式，其中一个锰亚基通过各向异性交换与一个配位不饱和的锰离子发生铁磁相互作用。这些结果解析并定义了S态的结构异质性，为S到S的转变、底物身份和传递途径以及O - O键形成机制提供了限制条件。
