Vassiliev Sergey, Zaraiskaya Tatiana, Bruce Doug
Department of Biology, Brock University, St. Catharines, Canada.
Biochim Biophys Acta. 2012 Sep;1817(9):1671-8. doi: 10.1016/j.bbabio.2012.05.016. Epub 2012 Jun 6.
The Mn(4)Ca cluster of the oxygen-evolving complex (OEC) of photosynthesis catalyzes the light-driven splitting of water into molecular oxygen, protons, and electrons. The OEC is buried within photosystem II (PSII), a multisubunit integral membrane protein complex, and water must find its way to the Mn(4)Ca cluster by moving through protein. Molecular dynamics simulations were used to determine the energetic barriers for water permeation though PSII extrinsic proteins. Potentials of mean force (PMFs) for water were derived by using the technique of multiple steered molecular dynamics (MSMD). Calculation of free energy profiles for water permeation allowed us to characterize previously identified water channels, and discover new pathways for water movement toward the Mn(4)Ca cluster. Our results identify the main constriction sites in these pathways which may serve as selectivity filters that restrict both the access of solutes detrimental to the water oxidation reaction and loss of Ca(2+) and Cl(-) from the active site.
光合作用放氧复合体（OEC）中的锰（4）钙簇催化光驱动的水分解为分子氧、质子和电子。OEC埋藏在光系统II（PSII）中，PSII是一种多亚基整合膜蛋白复合体，水必须通过蛋白质移动才能到达锰（4）钙簇。分子动力学模拟用于确定水透过PSII外在蛋白的能量屏障。通过使用多引导分子动力学（MSMD）技术得出了水的平均力势（PMF）。水渗透自由能分布的计算使我们能够表征先前确定的水通道，并发现水向锰（4）钙簇移动的新途径。我们的结果确定了这些途径中的主要收缩位点，这些位点可能作为选择性过滤器，限制对水氧化反应有害的溶质的进入以及活性位点中钙离子和氯离子的流失。
