Dau Holger, Grundmeier Alexander, Loja Paola, Haumann Michael
Freie Universität Berlin, FB Physik, Arnimallee 14, 14195 Berlin, Germany.
Philos Trans R Soc Lond B Biol Sci. 2008 Mar 27;363(1494):1237-43; discussion 1243-4. doi: 10.1098/rstb.2007.2220.
The water-oxidizing manganese complex bound to the proteins of photosystem II (PSII) was studied by X-ray absorption spectroscopy on PSII membrane particles. An extended range for collection of extended X-ray absorption fine-structure (EXAFS) data was used (up to 16.6A(-1)). The EXAFS suggests the presence of two Mn-Mn distances close to 2.7A (per Mn4Ca complex); the existence of a third Mn-Mn distance below 2.9A is at least uncertain. Interestingly, a distance of 3.7A is clearly resolved in the extended-range data and tentatively assigned to a Mn-Mn distance. Taking into account the above EXAFS results (inter alia), we present a model for the structure of the PSII manganese complex, which differs from previous atomic-resolution models. Emphasizing the hypothetical character, we propose for all semi-stable S-states: (i) a structure of the Mn4Ca(mu-O)n core, (ii) a model of the amino acid environment, and (iii) assignments of distinct Mn oxidation states to all the individual Mn ions. This specific working model may permit discussion, verification and invalidation of its various features in comparison with experimental and theoretical findings.
利用X射线吸收光谱对光系统II（PSII）膜颗粒上与蛋白质结合的水氧化锰复合物进行了研究。采用了扩展范围来收集扩展X射线吸收精细结构（EXAFS）数据（高达16.6 Å⁻¹）。EXAFS表明存在两个接近2.7 Å的Mn-Mn距离（每个Mn₄Ca复合物）；第三个低于2.9 Å的Mn-Mn距离的存在至少是不确定的。有趣的是，在扩展范围数据中清楚地分辨出3.7 Å的距离，并初步将其指定为Mn-Mn距离。考虑到上述EXAFS结果（尤其如此），我们提出了一个PSII锰复合物的结构模型，该模型与以前的原子分辨率模型不同。强调其假设性质，我们针对所有半稳定S态提出：（i）Mn₄Ca（μ-O）ₙ核心的结构，（ii）氨基酸环境的模型，以及（iii）将不同的Mn氧化态分配给所有单个Mn离子。这个特定的工作模型可能允许与实验和理论结果相比，对其各种特征进行讨论、验证和证伪。
