QM/MM computational studies of substrate water binding to the oxygen-evolving centre of photosystem II
QM/MM computational studies of substrate water binding to the oxygen-evolving centre of photosystem II
复制标题
DOI：
10.1098/rstb.2007.2210
复制
发表时间：
2008-03-27
影响因子：
6.3
通讯作者：
Batista, Victor S.
中科院分区：
文献类型：
--
作者：
Sproviero, Eduardo M.;Shinopoulos, Katherine;Batista, Victor S.
本文报道了底物水与光系统 II (PSII) 的释氧中心 (OEC) 结合的计算研究，通过氨基酸残基、水、氢氧化物和氯化物完全连接。这些计算基于 PSII 的 OEC 的量子力学/分子力学混合模型，该模型是最近与来自蓝细菌 Thermosynechococcus elongatus 的 PSII 的 X 射线晶体结构结合开发的。 OEC 模型涉及立方体 Mn3CaO4Mn 金属簇，其中三个紧密关联的锰离子与单个 mu 4-氧配位的 Mn 离子相连，通常称为“悬挂锰”。与钙结合的两个水分子和悬挂的锰被认为是底物分子，负责分子氧的形成。结果发现，Mn(4) 结合水的能垒与模型配合物的能垒非常吻合。然而，钙结合水的障碍要大得多。水结合不仅与金属中心的形式氧化态相关，而且与它们相应的由电荷转移相互作用调节的静电势原子电荷相关。水交换过程中结构重排的计算为实验发现提供了支持，即与钙配位的水分子与附着在悬空锰上的水分子相比，与大量 O-18 标记水的交换率应该更小。模型还预测 S-1 -> S-2 转变会对两种水交换率产生相反的影响。
This paper reports computational studies of substrate water binding to the oxygen-evolving centre (OEC) of photosystem II (PSII), completely ligated by amino acid residues, water, hydroxide and chloride. The calculations are based on quantum mechanics/molecular mechanics hybrid models of the OEC of PSII, recently developed in conjunction with the X-ray crystal structure of PSII from the cyanobacterium Thermosynechococcus elongatus. The model OEC involves a cuboidal Mn3CaO4Mn metal cluster with three closely associated manganese ions linked to a single mu 4-oxo-ligated Mn ion, often called the 'dangling manganese'. Two water molecules bound to calcium and the dangling manganese are postulated to be substrate molecules, responsible for dioxygen formation. It is found that the energy barriers for the Mn(4)-bound water agree nicely with those of model complexes. However, the barriers for Ca-bound waters are substantially larger. Water binding is not simply correlated to the formal oxidation states of the metal centres but rather to their corresponding electrostatic potential atomic charges as modulated by charge-transfer interactions. The calculations of structural rearrangements during water exchange provide support for the experimental finding that the exchange rates with bulk O-18-labelled water should be smaller for water molecules coordinated to calcium than for water molecules attached to the dangling manganese. The models also predict that the S-1 -> S-2 transition should produce opposite effects on the two water-exchange rates.