Department of Chemical, Biological & Macro-Molecular Sciences, S. N. Bose National Centre for Basic Sciences, Kolkata, West Bengal 700106, India.
Research Center for Advanced Science and Technology, The University of Tokyo, 4-6-1 Komaba, Meguro-ku, Tokyo 153-8904, Japan.
J Phys Chem B. 2022 Jan 13;126(1):123-131. doi: 10.1021/acs.jpcb.1c09176. Epub 2021 Dec 25.
In photosystem II (PSII), Cl is a prerequisite for the second flash-induced oxidation of the MnCaO cluster (the S to S transition). We report proton transfer from the substrate water molecule via D1-Asp61 and electron transfer via redox-active D1-Tyr161 (TyrZ) to the chlorophyll pair in Cl-depleted PSII using a quantum mechanical/molecular mechanical approach. The low-barrier H-bond formation between the substrate water molecule and D1-Asp61 remained unaffected upon the depletion of Cl. However, the binding site, D2-Lys317, formed a salt bridge with D1-Asp61, leading to the inhibition of the subsequent proton transfer. Remarkably, the redox potential () of S/S increased significantly, making electron transfer from S to TyrZ energetically uphill, as observed in Ca-depleted PSII. The uphill electron transfer pathway was induced by the significant increase in (S/S) caused by the loss of charge compensation for D2-Lys317 upon the depletion of Cl, whereas it was induced by the significant decrease in (TyrZ) caused by the rearrangement of the water molecules at the Ca binding moiety upon the depletion of Ca.
在光系统 II（PSII）中，Cl 是 MnCaO 簇（S 到 S 跃迁）第二次闪光诱导氧化的前提。我们报告了使用量子力学/分子力学方法从基质水分子通过 D1-Asp61 进行质子转移，并通过氧化还原活性 D1-Tyr161（TyrZ）进行电子转移到 Cl 耗尽的 PSII 中的叶绿素对。Cl 耗尽后，基质水分子与 D1-Asp61 之间的低能垒氢键形成不受影响。然而，结合位点 D2-Lys317 与 D1-Asp61 形成盐桥，导致随后的质子转移受到抑制。值得注意的是，S/S 的氧化还原电势（）显着增加，使得电子从 S 到 TyrZ 的转移在能量上是上坡的，这在 Ca 耗尽的 PSII 中观察到。Cl 耗尽时，由于 D2-Lys317 失去电荷补偿，（S/S）显着增加，从而诱导上坡电子转移途径，而 Ca 耗尽时，由于 Ca 结合部位的水分子重新排列，（TyrZ）显着降低，从而诱导上坡电子转移途径。
