Department of Chemistry, University of California, Davis, CA, 95616, USA.
Department of Chemistry, Faculty of Science, Mahidol University, Bangkok, 10400, Thailand.
Photosynth Res. 2023 Jun;156(3):309-314. doi: 10.1007/s11120-023-00998-z. Epub 2023 Jan 18.
The residue D1-D170 bridges Mn4 with the Ca ion in the O-evolving MnCaO cluster of Photosystem II. Recently, the D1-D170E mutation was shown to substantially alter the S-minus-S FTIR difference spectra [Debus RJ (2021) Biochemistry 60:3841-3855]. The mutation was proposed to alter the equilibrium between different Jahn-Teller conformers of the S state such that (i) a different S state conformer is stabilized in D1-D170E than in wild-type and (ii) the S to S transition in D1-D170E produces a high-spin form of the S state rather than the low-spin form that is produced in wild-type. In this study, we employed EPR spectroscopy to test if a high-spin form of the S state is formed preferentially in D1-D170E PSII. Our data show that illumination of dark-adapted D1-D170E PSII core complexes does indeed produce a high-spin form of the S state rather than the low-spin multiline form that is produced in wild-type. This observation provides further experimental support for a change in the equilibrium between S state conformers in both the S and S states in a site-directed mutant that retains substantial O evolving activity.
残基 D1-D170 将 Mn4 与 PSII 中 O 演化 MnCaO 簇中的 Ca 离子桥接。最近，D1-D170E 突变被证明会极大地改变 S-减 S FTIR 差光谱[Debus RJ（2021）生物化学 60:3841-3855]。该突变被认为改变了 S 态不同 Jahn-Teller 构象之间的平衡，使得 (i) D1-D170E 中的不同 S 态构象得到稳定，而在野生型中则不然，以及 (ii) D1-D170E 中的 S 到 S 跃迁产生 S 态的高自旋形式，而不是在野生型中产生的低自旋形式。在这项研究中，我们采用 EPR 光谱技术来测试 D1-D170E PSII 中是否优先形成 S 态的高自旋形式。我们的数据表明，对暗适应的 D1-D170E PSII 核心复合物进行光照确实会产生 S 态的高自旋形式，而不是在野生型中产生的低自旋多线形式。这一观察结果为在保留大量 O 演化活性的定点突变体中，S 态和 S 态之间 S 态构象平衡的改变提供了进一步的实验支持。
