Conlan Brendon, Cox Nicholas, Su Ji-Hu, Hillier Warwick, Messinger Johannes, Lubitz Wolfgang, Dutton P Leslie, Wydrzynski Tom
Australian National University, Canberra, Australia.
Biochim Biophys Acta. 2009 Sep;1787(9):1112-21. doi: 10.1016/j.bbabio.2009.04.011. Epub 2009 May 3.
Photosynthesis involves the conversion of light into chemical energy through a series of electron transfer reactions within membrane-bound pigment/protein complexes. The Photosystem II (PSII) complex in plants, algae and cyanobacteria catalyse the oxidation of water to molecular O2. The complexity of PSII has thus far limited attempts to chemically replicate its function. Here we introduce a reverse engineering approach to build a simple, light-driven photo-catalyst based on the organization and function of the donor side of the PSII reaction centre. We have used bacterioferritin (BFR) (cytochrome b1) from Escherichia coli as the protein scaffold since it has several, inherently useful design features for engineering light-driven electron transport. Among these are: (i.) a di-iron binding site; (ii.) a potentially redox-active tyrosine residue; and (iii.) the ability to dimerise and form an inter-protein heme binding pocket within electron tunnelling distance of the di-iron binding site. Upon replacing the heme with the photoactive zinc-chlorin e6 (ZnCe6) molecule and the di-iron binding site with two manganese ions, we show that the two Mn ions bind as a weakly coupled di-nuclear Mn2II,II centre, and that ZnCe6 binds in stoichiometric amounts of 1:2 with respect to the dimeric form of BFR. Upon illumination the bound ZnCe6 initiates electron transfer, followed by oxidation of the di-nuclear Mn centre possibly via one of the inherent tyrosine residues in the vicinity of the Mn cluster. The light dependent loss of the MnII EPR signals and the formation of low field parallel mode Mn EPR signals are attributed to the formation of MnIII species. The formation of the MnIII is concomitant with consumption of oxygen. Our model is the first artificial reaction centre developed for the photo-catalytic oxidation of a di-metal site within a protein matrix which potentially mimics water oxidation centre (WOC) photo-assembly.
光合作用涉及通过膜结合色素/蛋白质复合物内的一系列电子转移反应将光能转化为化学能。植物、藻类和蓝细菌中的光系统II（PSII）复合物催化水氧化为分子氧。PSII的复杂性迄今为止限制了化学复制其功能的尝试。在此，我们引入一种逆向工程方法，基于PSII反应中心供体侧的组织和功能构建一种简单的光驱动光催化剂。我们使用了来自大肠杆菌的细菌铁蛋白（BFR）（细胞色素b1）作为蛋白质支架，因为它具有几个对工程化光驱动电子传输固有有用的设计特征。其中包括：（i）一个双铁结合位点；（ii）一个潜在的氧化还原活性酪氨酸残基；以及（iii）二聚化并在双铁结合位点的电子隧穿距离内形成蛋白质间血红素结合口袋的能力。在用光活性锌-二氢卟吩e6（ZnCe6）分子取代血红素并用两个锰离子取代双铁结合位点后，我们表明两个锰离子以弱耦合的双核MnII,II中心形式结合，并且ZnCe6相对于BFR的二聚体形式以化学计量比1:2结合。光照后，结合的ZnCe6启动电子转移，随后双核锰中心可能通过锰簇附近的一个固有酪氨酸残基被氧化。MnII EPR信号的光依赖性损失和低场平行模式Mn EPR信号的形成归因于MnIII物种的形成。MnIII的形成与氧气消耗同时发生。我们的模型是第一个为在蛋白质基质中光催化氧化双金属位点而开发的人工反应中心，它可能模拟水氧化中心（WOC）的光组装。
