Dual-mode EPR detects the initial intermediate in photoassembly of the photosystem II mn cluster: The influence of amino acid residue 170 of the D1 polypeptide on Mn coordination
Dual-mode EPR detects the initial intermediate in photoassembly of the photosystem II mn cluster: The influence of amino acid residue 170 of the D1 polypeptide on Mn coordination
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DOI：
10.1021/ja000142t
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发表时间：
2000-04-19
影响因子：
15
通讯作者：
Britt, RD
中科院分区：
文献类型：
--
作者：
Campbell, KA;Force, DA;Britt, RD
我们报告的第一个平行极化EPR信号从锰（III）离子形成的光氧化锰（II）结合在高亲和力锰结合位点的光系统II（PSII）。该物种对应于水分解锰簇组装途径上形成的第一个光活化中间体。1.2/1化学计量Mn（II）/Mn耗尽野生型集胞藻属PCC 6803 PSII颗粒的光氧化产物的平行模式EPR谱由六个良好分辨的转换分裂由一个相对较小的Mn-55超精细耦合（44 G）。这种光谱特征是不存在的光氧化锰apoPSII复合物制备的D1-Asp 170 Glu和D1-Asp 170 His突变体，提供了直接的光谱证据的作用，这种特定的D1-Asp 170残基在初始的光活化化学。对野生型样品的Mn（III）平行模EPR信号进行的温度依赖性测量和光谱模拟给出了轴向零场分裂值D约为-2.5 cm（-1）和菱形零场分裂值\E\约为0.269 cm（-1）。该d（4）离子的负D值指示八面体cm Mn（III）几何结构的B-5（1g）对称基态或五配位正方锥体Mn（III）几何结构的B-5（1）对称基态。从野生型光氧化的Mn apoPSII复合物获得的平行模式Mn（III）EPR光谱与从天然Mn超氧化物歧化酶的五配位Mn（III）形式获得的平行模式Mn（III）EPR光谱形成对比，天然Mn超氧化物歧化酶具有三角双锥几何结构和（5）A（1）对称基态，产生正D值和大得多的100 G的55 Mn超精细耦合。D1-Asp 170 His突变体显示出类似于在Mn（III）模型复合物中观察到的平行模式EPR谱。D1-Asp 170 Glu突变体没有显示平行模式的光谱，但在垂直模式下，它在g = 5附近显示出具有S = 3/2 Mn（IV）离子光谱特征的宽特征。这表明该突变体提供了具有较低正Mn（III）/MnOV）还原电位的结合位点。
We report the first parallel polarization EPR signal from the Mn(III) ion formed by photooxidation of Mn(II) bound at the high affinity Mn-binding site of photosystem II (PSII). This species corresponds to the first photoactivation intermediate formed on the pathway to assembly of the water-splitting Mn cluster. The parallel mode EPR spectrum of the photooxidation product of 1.2/1 stoichiometry Mn(II)/Mn-depleted wildtype Synechocystis sp. PCC 6803 PSII particles consists of six well-resolved transitions split by a relatively small Mn-55 hyperfine coupling (44 G). This spectral signature is absent in photooxidized Mn apoPSII complexes prepared from D1-Asp170Glu and D1-Asp170His mutants, providing direct spectral evidence for a role for this specific D1-Asp170 residue in the initial photoactivation chemistry. Temperature-dependence measurements and spectral simulations performed on the Mn(III) parallel mode EPR signal of the wild-type sample give an axial zero-field splitting value of D approximate to -2.5 cm(-1) and a rhombic zero-field splitting value of \E\ approximate to 0.269 cm(-1). The negative D value for this d(4) ion is indicative of either a B-5(1g) symmetry ground state of an octahedral cm Mn(III) geometry or a B-5(1) symmetry ground state of a five-coordinate square-pyramidal Mn(III) geometry. The parallel mode Mn(III) EPR spectrum obtained from the wild-type photooxidized Mn apoPSII complex is contrasted with that obtained from the five-coordinate Mn(III) form of native Mn superoxide dismutase, which has a trigonal-bipyramidal geometry and a (5)A(1) symmetry ground state giving rise to a positive D value and a much larger 55Mn hyperfine coupling of 100 G. The D1-Asp170His mutant displays a parallel mode EPR spectrum similar to that observed in a Mn(III) model complex. The D1-Asp170Glu mutant shows no parallel mode spectrum, but in perpendicular mode it shows a broad feature near g = 5 which has spectral characteristics of an S = 3/2 Mn(IV) ion. This suggests that this mutant provides a binding site with a less positive Mn(III)/MnOV) reduction potential.