Quinone redox tuning for regulation and protection of the water splitting enzyme

用于调节和保护水分解酶的醌氧化还原调节

• 批准号: BB/R00921X/1
• 负责人: Alfred Rutherford
• 金额: $ 81.79万
• 依托单位: Imperial College London
• 依托单位国家: 英国
• 项目类别: Research Grant
• 财政年份: 2018
• 资助国家: 英国
• 起止时间: 2018 至 无数据
• 项目状态: 已结题
• 来源: https://gtr.ukri.org/projects?ref=BB%2FR00921X%2F1
• 关键词: Quinone; redox; tuning; regulation; protection

Photosynthesis is the process that converts solar energy into the chemical energy that powers life. The light is used to split water, removing some of its electrons and using them to pull down carbon dioxide from the atmosphere to make the building blocks and fuel for life. When water is split in this way, protons (hydrogen ions) and oxygen are released. The oxygen accumulates in the atmosphere, reacting with UV to form the protective ozone layer. The oxygen also provides a reactive environment that allows respiration to occur. Both of these roles of oxygen were crucial for the development of multicellular organisms: life as we know it.The most important photosynthetic enzyme is Photosystem II, the water splitting enzyme. It is the enzyme that changed the planet. Water is very unreactive and splitting it is hard to do. An enzyme capable of splitting water seems to have evolved only once and all O2-producing photosynthesizers, from the most ancient cyanobacterium to the oak tree, use the same enzyme.Such difficult chemistry requires a lot of energy and this comes from sunlight. The amount of energy in light depends on its colour and Photosystem II uses red light absorbed by a pigment called chlorophyll a. The energy available in the light collected by chlorophyll is not enough to do what PSII does safely and although evolution has provided it with an impressive bag of chemical tricks designed to protect it from burning out, in the end it just takes the hit. It is destroyed after about a million reactions (about every half hour, depending on the brightness of the sunlight), and it then needs to be taken apart and the damaged subunits replaced with new ones. This damage and repair costs energy and under severe conditions it can limit plant growth and give smaller crop yields.The present study is focused on discovering and understanding the tricks for protecting Photosystem II. We have previously found some interesting stuff. The damage occurs in PSII when the light is there, the system is ready to work but it can't do anything useful with the energy because something prevents the completion of the hot chemistry. When this happens the light-generated charges come back together again forming a high energy state of chlorophyll called a triplet. The triplet chlorophyll reacts with normal oxygen and turns it into a super-reactive form called singlet oxygen, which is the real killer. This causes the damage to Photosystem II. In principle this damage could happen when electrons don't come from water, for example prior to the assembly of the water splitting catalyst, or when there is nowhere to put the electrons because of a downstream block, for example due to a lack of CO2 to fix. But in both of these cases burnout is minimised because a component called QA has its reactivity tuned down so that the energy is dumped as heat instead of doing the high energy reactions that form the triplet. When the water splitting part is assembled, or when the CO2 levels return to normal, QA is switched back to its high energy function. We are now looking closely at how the next component in the chain, QB, works and if it too is tuned or controlled in a different way or indeed if it helps to tune its neighbour QA. Already we have had surprises and it seems QB works very differently from how some researchers thought. By understanding the details of PSII damage and protection mechanisms, better strategies may be developed for making photosynthesis more efficient and increasing food production. Very recently other researchers got improved crop growth when they managed to accelerate (a different kind of) protective switching in plants. So this approach could just work.

光合作用是将太阳能转化为为生命提供动力的化学能的过程。光用于分解水，去除其中的一些电子，并利用它们从大气中吸收二氧化碳，从而制造生命的基石和燃料。当水以这种方式分裂时，会释放出质子（氢离子）和氧气。氧气在大气中积聚，与紫外线发生反应，形成保护性臭氧层。氧气还提供了允许呼吸发生的反应环境。氧的这两种作用对于多细胞生物体（我们所知的生命）的发育至关重要。最重要的光合酶是光系统 II，即水分解酶。正是这种酶改变了地球。水的反应活性非常低，很难分解。一种能够分解水的酶似乎只进化了一次，所有产生氧气的光合作用器，从最古老的蓝细菌到橡树，都使用同一种酶。这种困难的化学反应需要大量能量，而这来自阳光。光的能量大小取决于其颜色，Photosystem II 使用被称为叶绿素 a 的色素吸收的红光。叶绿素收集的光中提供的能量不足以安全地完成 PSII 的任务，尽管进化为它提供了一系列令人印象深刻的化学技巧，旨在保护它不被烧毁，但最终它只是受到了打击。它在大约一百万次反应后被破坏（大约每半小时一次，取决于阳光的亮度），然后需要将其拆开，并用新的子单元替换损坏的子单元。这种损坏和修复需要消耗能源，在恶劣的条件下，它会限制植物生长并降低作物产量。本研究的重点是发现和理解保护光系统 II 的技巧。我们之前发现了一些有趣的东西。当光存在时，PSII 就会发生损坏，系统已准备好工作，但它无法利用能量做任何有用的事情，因为某些东西阻止了热化学反应的完成。当这种情况发生时，光产生的电荷再次聚集在一起，形成叶绿素的高能态，称为三重态。三重态叶绿素与普通氧发生反应，将其转化为一种称为单线态氧的超活性形式，这是真正的杀手。这会导致 Photosystem II 损坏。原则上，当电子不是来自水时，例如在水分解催化剂组装之前，或者由于下游阻塞而无处放置电子时，例如由于缺乏需要修复的二氧化碳，则可能会发生这种损坏。但在这两种情况下，倦怠都被最小化，因为一种称为 QA 的成分的反应性被调低，这样能量就会以热量的形式释放出来，而不是进行形成三重态的高能反应。当水分解部分组装完毕，或者当二氧化碳水平恢复正常时，QA 切换回其高能功能。我们现在正在密切关注链中的下一个组件 QB 如何工作，以及它是否也以不同的方式进行调整或控制，或者是否有助于调整其相邻的 QA。我们已经有了惊喜，而且 QB 的工作方式似乎与一些研究人员的想法非常不同。通过了解 PSII 损伤和保护机制的细节，可以制定更好的策略来提高光合作用的效率并增加粮食产量。最近，其他研究人员成功地加速了植物的（另一种）保护性转换，从而改善了作物的生长。所以这种方法是可行的。

项目成果

Femtosecond visible transient absorption spectroscopy of chlorophyll- f -containing photosystem II

含叶绿素f光系统II的飞秒可见瞬态吸收光谱

• DOI: 10.1073/pnas.2006016117
• 发表时间: 2020
• 期刊: Proceedings of the National Academy of Sciences
• 作者: Zamzam N

Oxygenic Photoreactivity in Photosystem II Studied by Rotating Ring Disk Electrochemistry.

• DOI: 10.1021/jacs.8b08784
• 发表时间: 2018-12-26
• 期刊: Journal of the American Chemical Society
• 影响因子: 15
• 作者: Kornienko N;Zhang JZ;Sokol KP;Lamaison S;Fantuzzi A;van Grondelle R;Rutherford AW;Reisner E
• 通讯作者: Reisner E