Proteo-Science Research Center, Ehime University, Matsuyama, 790-8577, Japan.
Department of Chemistry, Graduate School of Science and Technology, Ehime University, Matsuyama, 790-8577, Japan.
Physiol Plant. 2021 Feb;171(2):183-199. doi: 10.1111/ppl.13115. Epub 2020 May 20.
The Mn CaO cluster of photosystem II (PSII) advances sequentially through five oxidation states (S to S ). Under the enzyme cycle, two water molecules are oxidized, O is generated and four protons are released into the lumen. Umena et al. (2011) have proposed that, with other charged amino acids, the R323 residue of the D1 protein could contribute to regulate a proton egress pathway from the Mn CaO cluster and Tyr via a proton channel identified from the 3D structure. To test this suggestion, a PsbA3/R323E site-directed mutant has been constructed and the properties of its PSII have been compared to those of the PsbA3-PSII by using EPR spectroscopy, polarography, thermoluminescence and time-resolved UV-visible absorption spectroscopy. Neither the oscillations with a period four nor the kinetics and S-state-dependent stoichiometry of the proton release were affected. However, several differences have been found: (1) the P decay in the hundreds of ns time domain was much slower in the mutant, (2) the S Q /DCMU and S Q /DCMU radiative charge recombination occurred at higher temperatures and (3) the S Tyr , S Tyr , S Tyr split EPR signals induced at 4.2 K by visible light from the S Tyr , S Tyr , S Tyr , respectively, and the (S Tyr )' induced by NIR illumination at 4.2 K of the S Tyr state differed. It is proposed that the R323 residue of the D1 protein interacts with Tyr likely via the H-bond network previously proposed to be a proton channel. Therefore, rather than participating in the egress of protons to the lumen, this channel could be involved in the relaxations of the H-bonds around Tyr by interacting with the bulk, thus tuning the driving force required for Tyr oxidation.
光合作用系统 II（PSII）中的 MnCaO 簇顺次经历五个氧化态（S 到 S ）。在酶循环中，两个水分子被氧化，O 生成，四个质子被释放到腔室中。Umena 等人（2011 年）提出，与其他带电氨基酸一起，D1 蛋白的 R323 残基可能有助于通过从 3D 结构中鉴定的质子通道调节从 MnCaO 簇和 Tyr 中排出质子的途径。为了验证这一假设，构建了 PsbA3/R323E 定点突变体，并通过使用 EPR 光谱、极谱法、热致发光和时间分辨紫外可见吸收光谱，比较了其 PSII 的性质与 PsbA3-PSII 的性质。质子释放的振荡周期为四、动力学和 S 态依赖性化学计量都没有受到影响。然而，发现了几个差异：（1）在突变体中，P 衰减在数百纳秒的时间域中要慢得多，（2）S Q /DCMU 和 S Q /DCMU 辐射电荷复合发生在更高的温度下，（3）S Tyr 、S Tyr 、S Tyr 分别在 4.2 K 下由 S Tyr 、S Tyr 、S Tyr 诱导的 EPR 信号分裂，以及由 S Tyr 状态下的近红外照射在 4.2 K 下诱导的（S Tyr ）'不同。提出 D1 蛋白的 R323 残基可能通过先前提出的质子通道氢键网络与 Tyr 相互作用。因此，该通道不是参与质子向腔室的排出，而是可能通过与本体相互作用来参与 Tyr 周围氢键的弛豫，从而调节 Tyr 氧化所需的驱动力。
