Rapid loss of structural motifs in the manganese complex of oxygenic photosynthesis by x-ray irradiation at 10-300 K
Rapid loss of structural motifs in the manganese complex of oxygenic photosynthesis by x-ray irradiation at 10-300 K
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DOI：
10.1074/jbc.m509724200
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发表时间：
2006-02-24
影响因子：
4.8
通讯作者：
Dau, H
中科院分区：
文献类型：
--
作者：
Grabolle, M;Haumann, M;Dau, H
通过X-射线吸收光谱在锰K-边的水氧化四锰配合物的光系统II的X-射线照射引起的光还原后的结构变化进行了研究。光还原与X射线剂量成正比。在较高氧化的S-2状态下比在S-1中更快;似乎金属位点的氧化电位决定了速率。在15 K下的S-1状态的X射线照射最初引起单电子还原为S-0*，伴随着锰原子之间的一个二-mu-氧代桥的转化，所述锰原子之前以类似于2.7埃的距离分离，以单-mu-氧代基序。此后，锰光还原慢100倍，其速率在10和300 K之间的双相增加，在类似于200 K的断点表明，蛋白质动力学是限速的自由基化学。对于在与蛋白质晶体学中所应用的类似的X射线剂量下的光还原，即使在10 K下，也观察到在最终Mn-4（II）状态的中途，由于锰离子之间的μ-氧桥的破坏，锰离子间距离< 3埃的完全丧失。这些结果提出了一些问题，从最近的蛋白质晶体学数据的光系统II的结构属性。建议采用受控的X射线光还原在金属蛋白质的研究：（i）人口的不同的还原状态，（ii）估计埋金属中心的氧化还原电位，和（iii）蛋白质动力学的研究。
Structural changes upon photoreduction caused by x-ray irradiation of the water-oxidizing tetramanganese complex of photosystem II were investigated by x-ray absorption spectroscopy at the manganese K-edge. Photoreduction was directly proportional to the x-ray dose. It was faster in the higher oxidized S-2 state than in S-1; seemingly the oxidizing potential of the metal site governs the rate. X-ray irradiation of the S-1 state at 15 K initially caused single-electron reduction to S-0* accompanied by the conversion of one di-mu-oxo bridge between manganese atoms, previously separated by similar to 2.7 angstrom, to a mono-mu-oxo motif. Thereafter, manganese photoreduction was 100 times slower, and the biphasic increase in its rate between 10 and 300 K with a breakpoint at similar to 200 K suggests that protein dynamics is rate-limiting the radical chemistry. For photoreduction at similar x-ray doses as applied in protein crystallography, halfway to the final Mn-4(II) state the complete loss of inter-manganese distances < 3 angstrom was observed, even at 10 K, because of the destruction of mu-oxo bridges between manganese ions. These results put into question some structural attributions from recent protein crystallography data on photosystem II. It is proposed to employ controlled x-ray photoreduction in metalloprotein research for: (i) population of distinct reduced states, (ii) estimating the redox potential of buried metal centers, and (iii) research on protein dynamics.