Fourier transform infrared detection of a polarizable proton trapped between photooxidized tyrosine Yz and a coupled histidine in photosystem II : Relevance to the proton transfer mechanism of water oxidation
Fourier transform infrared detection of a polarizable proton trapped between photooxidized tyrosine Yz and a coupled histidine in photosystem II : Relevance to the proton transfer mechanism of water oxidation
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光系统 II 中光氧化酪氨酸 Yz 和偶联组氨酸之间捕获的可极化质子的傅里叶变换红外检测：与水氧化的质子转移机制的相关性
DOI：
10.1021/bi500237y
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发表时间：
2014
期刊：
影响因子：
2.9
通讯作者：
T. Noguchi
中科院分区：
文献类型：
--
作者：
S. Nakamura;R. Nagao;R. Takahashi;and T. NoguchiS. Nakamura;R. Nagao;R. Takahashi;T. Noguchi
光系统II（PSII）中具有氧化还原活性的酪氨酸YZ（D1-Tyr 161）是Mn 4Ca簇的直接电子受体，Mn 4Ca簇是光合水氧化的催化中心。YZ也位于连接Mn 4Ca簇与内腔的氢键网络中，因此可能与水氧化过程中的质子转移过程有关。为了理解YZ在水氧化机理中的作用，我们利用光诱导傅里叶变换红外（FTIR）差谱研究了YZ与其光氧化中性自由基YZ·的氢键相互作用以及偶联的His残基D1-His 190的相互作用.在2800 cm-1附近，Mn耗尽的PSII核心复合物的YZ·--YZ FTIR差谱显示出一个宽的正特征，这在另一种氧化还原活性酪氨酸YD（D2-Tyr 160）的相应光谱中是不存在的。通过15 N和H/D取代、pH依赖性的研究以及密度泛函理论和量子力学/分子力学（QM/MM）计算表明，该谱带来自D1-His 190质子化阳离子的N-H伸缩振动，与YZ·形成电荷辅助强氢键。这一结果提供了强有力的证据，表明YZ氧化后释放的质子被捕获在D1-His 190中，并且正电荷保留在该His上。2800 cm-1的宽谱带反映了YZ·和HisH+之间氢键的质子极化率很大。QM/MM计算进一步表明，YZ氧化后，氢键网络重排，一个水分子向D1-His 190移动。根据这些数据，提出了一种新的质子转移机制，通过YZ·-HisH+，其中HisH+的可极化质子跳跃到这个水触发质子从基底水转移到管腔侧。这种质子转移机制可能在S2→ S3转变中起作用，这需要在电子转移之前释放质子，因为Mn 4Ca簇上有过量的正电荷。
The redox-active tyrosine YZ(D1-Tyr161) in photosystem II (PSII) functions as an immediate electron acceptor of the Mn4Ca cluster, which is the catalytic center of photosynthetic water oxidation. YZis also located in the hydrogen bond network that connects the Mn4Ca cluster to the lumen and hence is possibly related to the proton transfer process during water oxidation. To understand the role of YZin the water oxidation mechanism, we have studied the hydrogen bonding interactions of YZand its photooxidized neutral radical YZ•together with the interaction of the coupled His residue, D1-His190, using light-induced Fourier transform infrared (FTIR) difference spectroscopy. The YZ•-minus-YZFTIR difference spectrum of Mn-depleted PSII core complexes exhibited a broad positive feature around 2800 cm–1, which was absent in the corresponding spectrum of another redox-active tyrosine YD(D2-Tyr160). Analyses by15N and H/D substitutions, examination of the pH dependence, and density functional theory and quantum mechanics/molecular mechanics (QM/MM) calculations showed that this band arises from the N–H stretching vibration of the protonated cation of D1-His190 forming a charge-assisted strong hydrogen bond with YZ•. This result provides strong evidence that the proton released from YZupon its oxidation is trapped in D1-His190 and a positive charge remains on this His. The broad feature of the ∼2800 cm–1band reflects a large proton polarizability in the hydrogen bond between YZ•and HisH+. QM/MM calculations further showed that upon YZoxidation the hydrogen bond network is rearranged and one water molecule moves toward D1-His190. From these data, a novel proton transfer mechanism via YZ•-HisH+is proposed, in which hopping of the polarizable proton of HisH+to this water triggers the transfer of the proton from substrate water to the luminal side. This proton transfer mechanism could be functional in the S2→ S3transition, which requires proton release before electron transfer because of an excess positive charge on the Mn4Ca cluster.