Electron transfer pathways from the S2-states to the S3-states either after a Ca2+/Sr2+ or a Cl-/I- exchange in Photosystem II from
Electron transfer pathways from the S2-states to the S3-states either after a Ca2+/Sr2+ or a Cl-/I- exchange in Photosystem II from
复制标题
DOI：
10.1016/j.bbabio.2015.03.006
复制
发表时间：
2015-06-01
影响因子：
4.3
通讯作者：
Sugiura, Miwa
中科院分区：
文献类型：
--
作者：
Boussac, Alain;Rutherford, A. William;Sugiura, Miwa
光系统II（PSII）中的水氧化位点在O-2形成之前经历五个连续的氧化态（S-0到S-4）。它由靠近氧化还原活性酪氨酸残基（Y-z）的Mn 4CaO 5-簇组成。Cl也是酶活性所必需的。通过使用EPR光谱，它已被证明，Ca ~（2+）/Sr ~（2+）交换和Cl ~-/I ~-交换扰动的中心的比例，显示高（S = 5/2）和低自旋（S = 1/2）形式的Systate。还发现S-3-态是异质的，具有：i）S = 3形式，其可通过EPR检测并且对近红外光不敏感;和ii）不是EPR可见的形式，但是其中Mn光化学发生，导致在近红外照射时形成（S2 Yz）'分裂EPR信号。在Sr/Cl-PSII中，S-2的高自旋（S = 5/2）形式显示出显著的不均匀性，在低温下产生g = 4.3的形式，在较高温度下在g = 4.9转化为松弛形式。高自旋g = 4.9态在低至180 K的温度下可以发展为EPR可探测的S-3态，而低自旋（S = 1/2）S-2态只能在>= 235 K的温度下发展为S-3态。两个S-2构型和两个S-3构型都显示在≥ 235 K时处于平衡状态，但在198 K时不处于平衡状态。由于两种S-2构型都是在198 K下形成的，它们可能来自两种特定的Si种群。在Si，Sy和S-3状态的异质群体的存在可能与结构的灵活性相关的定位的氧O-5内的集群中突出的计算方法，并已链接到基板交换。这些数据的背景下讨论的电子转移途径之间的S-2-状态（S）和S-3-状态（S）的最近在硅片上的研究。
The site for water oxidation in Photosystem II (PSII) goes through five sequential oxidation states (S-0 to S-4) before O-2 is evolved. It consists of a Mn4CaO5-cluster close to a redox-active tyrosine residue (Y-z). Cl is also required for enzyme activity. By using EPR spectroscopy it has been shown that both Ca2+/Sr2+ exchange and Cl-/I- exchange perturb the proportions of centers showing high (S = 5/2) and low spin (S = 1/2) forms of the Systate. The S-3-state was also found to be heterogeneous with: i) a S = 3 form that is detectable by EPR and not sensitive to near-infrared light; and ii) a form that is not EPR visible but in which Mn photochemistry occurs resulting in the formation of a (S2Yz)' split EPR signal upon near-infrared illumination. In Sr/Cl-PSII, the high spin (S = 5/2) form of S-2 shows a marked heterogeneity with a g = 4.3 form generated at low temperature that converts to a relaxed form at g = 4.9 at higher temperatures. The high spin g = 4.9 form can then progress to the EPR detectable form of S-3 at temperatures as low as 180 K whereas the low spin (S = 1/2) S-2-state can only advance to the S-3 state at temperatures >= 235 K. Both of the two S-2 configurations and the two S-3 configurations are each shown to be in equilibrium at >= 235K but not at 198 K. Since both S-2 configurations are formed at 198 K, they likely arise from two specific populations of Si. The existence of heterogeneous populations in Si, Sy and S-3 states may be related to the structural flexibility associated with the positioning of the oxygen O-5 within the cluster highlighted in computational approaches and which has been linked to substrate exchange. These data are discussed in the context of recent in silico studies of the electron transfer pathways between the S-2-state(s) and the S-3-state(s).