Orientation of the tetranuclear manganese cluster and tyrosine Z in the O(2)-evolving complex of photosystem II: An EPR study of the S(2)Y(Z)(*) state in oriented acetate-inhibited photosystem II membranes.
Orientation of the tetranuclear manganese cluster and tyrosine Z in the O(2)-evolving complex of photosystem II: An EPR study of the S(2)Y(Z)(*) state in oriented acetate-inhibited photosystem II membranes.
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DOI：
10.1021/bi990780s
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发表时间：
1999-09
期刊：
影响因子：
2.9
通讯作者：
K. Lakshmi;S. Eaton;G. Eaton;G. Brudvig
中科院分区：
文献类型：
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作者：
K. Lakshmi;S. Eaton;G. Eaton;G. Brudvig
已知用醋酸盐进行抑制处理，然后进行光照和快速冷冻，可捕获光系统 II (PS II) 中 O(2) 演化复合物 (OEC) 的 S(2)Y(Z)(*) 态。由于酪氨酰自由基 Y(Z)(*) 与 Mn(4) 簇的 S = 1/2 S(2) 态的相互作用，该状态的 EPR 谱显示出宽的分裂信号。我们提出了一种新方法来分析一维（1-D）取向的乙酸盐抑制 PS II 膜的 S(2)Y(Z)(*) 光谱，以确定膜内 S(2)Y(Z)(*) 偶极矢量的大小和相对方向。尽管存在大量有关定向膜片中孤立自旋的 EPR 数据，但本研究是此类系统中偶极耦合电子自旋对的首次研究。我们证明了该技术的可行性，并建立了严格的治疗方法来解决部分取向一维膜制剂中存在的紊乱。我们发现（i）Y（Z）（*）和Mn（4）簇之间的点偶极子距离为7.9 +/- 0.2 A，（ii）自旋间矢量与类囊体膜法线之间的角度为75度，（iii）Mn（4）簇的g（z）（）轴与膜法线成70度，与自旋间矢量成35度，（iv）交换两个自旋之间的相互作用为-275 x 10(-)(4) cm(-)(1)，这是反铁磁性的。由于定向自旋耦合对的 EPR 线形状对自旋间距离的敏感性，本研究对 Y(Z)-Mn(4) 点偶极子距离施加比从随机定向样本获得的更严格的约束。从一维定向样本获得的几何约束与已发表的 Mn 耗尽 PS II 结构模型相结合，提出 Mn(4) 簇的位置。 Y(Z) 与锰结合的氢氧化物配体形成氢键的结构与现有数据一致，并且有利于两个氧化还原中心之间的最大轨道重叠，这将有利于直接的电子和质子转移步骤。
Inhibitory treatment by acetate, followed by illumination and rapid freezing, is known to trap the S(2)Y(Z)(*) state of the O(2)-evolving complex (OEC) in photosystem II (PS II). An EPR spectrum of this state exhibits broad split signals due to the interaction of the tyrosyl radical, Y(Z)(*), with the S = 1/2 S(2) state of the Mn(4) cluster. We present a novel approach to analyze S(2)Y(Z)(*) spectra of one-dimensionally (1-D) oriented acetate-inhibited PS II membranes to determine the magnitude and relative orientation of the S(2)Y(Z)(*) dipolar vector within the membrane. Although there exists a vast body of EPR data on isolated spins in oriented membrane sheets, the present study is the first of its kind on dipolar-coupled electron spin pairs in such systems. We demonstrate the feasibility of the technique and establish a rigorous treatment to account for the disorder present in partially oriented 1-D membrane preparations. We find that (i) the point-dipole distance between Y(Z)(*) and the Mn(4) cluster is 7.9 +/- 0.2 A, (ii) the angle between the interspin vector and the thylakoid membrane normal is 75 degrees, (iii) the g(z)()-axis of the Mn(4) cluster is 70 degrees away from the membrane normal and 35 degrees away from the interspin vector, and (iv) the exchange interaction between the two spins is -275 x 10(-)(4) cm(-)(1), which is antiferromagnetic. Due to the sensitivity of EPR line shapes of oriented spin-coupled pairs to the interspin distance, the present study imposes a tighter constraint on the Y(Z)-Mn(4) point-dipole distance than obtained from randomly oriented samples. The geometric constraints obtained from the 1-D oriented sample are combined with published models of the structure of Mn-depleted PS II to propose a location of the Mn(4) cluster. A structure in which Y(Z) is hydrogen bonded to a manganese-bound hydroxide ligand is consistent with available data and favors maximal orbital overlap between the two redox center that would facilitate direct electron- and proton-transfer steps.