Protein-protein interactions in the early stages of chlorophyll biosynthesis

叶绿素生物合成早期阶段的蛋白质-蛋白质相互作用

• 批准号: BB/D015413/1
• 负责人: Christopher Hunter
• 金额: $ 42.84万
• 依托单位: University of Sheffield
• 依托单位国家: 英国
• 项目类别: Research Grant
• 财政年份: 2006
• 资助国家: 英国
• 起止时间: 2006 至 无数据
• 项目状态: 已结题
• 来源: https://gtr.ukri.org/projects?ref=BB%2FD015413%2F1
• 关键词: Protein; protein; interactions; early; stages

Photosynthesis is the most important process occurring on Earth whereby carbon dioxide and water is converted into carbohydrate using light energy harnessed from the sun by the green pigment chlorophyll. All green plants, algae and several species of bacteria can carry out photosynthesis and it is ultimately the basis of all life on the planet. Photosynthesis is a multi-step process involving many chemical reactions catalysed by specialised proteins known as enzymes and a large number of other proteins that act with chlorophyll as a 'light harvesting complex (LHC)' to absorb light. Chlorophyll, and its chemical precursors, can be highly dangerous when not bound to LHC proteins, causing oxidative damage to the cell. Chlorophyll biosynthesis must therefore be tightly controlled and regulated to prevent such a build-up. The first committed step of chlorophyll biosynthesis is carried out by the multi-subunit enzyme magnesium (Mg) chelatase that is made up of the H, I and D subunits. This is a key enzyme as it lies at the branch point of tetrapyrolle biosynthesis. Chlorophyll and haem are the end products of this pathway; haem is produced by the enzyme ferrochelatase and plays a crucial role in the process of respiration which generates energy for the cells needs. Depending on the cell's requirements the two branches of this pathway need to be balanced; too much haem and/or too little chlorophyll and magnesium chelatase activity will be stimulated, too much chlorophyll and/or too little haem and ferrochelatase activity will be stimulated. One way in which Mg chelatase is stimulated is by the addition of a protein known as GUN4. This protein was originally described in the higher plant Arabidopsis where it is involved in one of the communication pathways from the chloroplast to the nucleus. Signalling through this pathway is mediated by the chlorophyll biosynthetic intermediate magnesium protoporphyrin IX produced by magnesium chelatase. Interestingly, whilst GUN4 acts as an 'accelerator' on Mg chelatase it works as a 'brake' on the next enzyme in the chlorophyll biosynthetic pathway, Mg proto methyltransferase (ChlM). In contrast, the H subunit of Mg chelatase stimulates the latter. These stimulations and inhibitions must be the result of physical interactions between GUN4, the chelatase and the methyltransferase. We will use various techniques to investigate interactions between H, I, D, ChlM and GUN4 using the purified proteins and also directly in the model green algae Synechocystis. Determining how these proteins interact with each other will give us an important insight into how chlorophyll biosynthesis is controlled and regulated. This work is of fundamental importance as it could provide a potential way of improving photosynthetic yield in plants, particularly under stress conditions.

光合作用是地球上发生的最重要的过程，通过利用来自太阳的光能，绿色色素叶绿素将二氧化碳和水转化为碳水化合物。所有绿色植物、藻类和几种细菌都可以进行光合作用，它最终是地球上所有生命的基础。光合作用是一个多步骤的过程，涉及许多化学反应，由被称为酶的特殊蛋白质和大量其他蛋白质催化，这些蛋白质与叶绿素一起作为吸收光的“光捕获复合体(LHC)”。当不与LHC蛋白结合时，叶绿素及其化学前体可能是高度危险的，会对细胞造成氧化损伤。因此，必须严格控制和调节叶绿素的生物合成，以防止这种积累。叶绿素生物合成的第一步是由由H、I和D亚基组成的多亚单位酶镁(Mg)螯合酶完成的。这是一个关键的酶，因为它位于四环素生物合成的分支点。叶绿素和血红素是这一途径的最终产物；血红素是由铁络合酶产生的，在呼吸过程中起着至关重要的作用，呼吸过程产生细胞所需的能量。根据细胞的需要，这一途径的两个分支需要平衡；太多的血红素和/或太少的叶绿素和镁螯合酶活性将被刺激，太多的叶绿素和/或太少的血红素和铁络合酶活性将被刺激。刺激镁螯合酶的一种方式是添加一种名为GUN4的蛋白质。这种蛋白最初在高等植物拟南芥中被描述，在那里它参与了从叶绿体到细胞核的一条通讯途径。通过这一途径的信号是由镁螯合酶产生的叶绿素生物合成中间体镁原卟啉IX介导的。有趣的是，虽然GUN4对镁螯合酶起到了‘加速器’的作用，但它却对叶绿素生物合成途径中的下一种酶--镁原甲基转移酶(ChlM)起到了‘刹车’作用。相反，镁螯合酶的H亚基刺激后者。这些刺激和抑制必须是GUN4、螯合酶和甲基转移酶之间物理相互作用的结果。我们将使用各种技术来研究H，I，D，ChlM和GUN4之间的相互作用，使用纯化的蛋白，也直接在模型绿藻聚球藻中。确定这些蛋白质是如何相互作用的，将使我们对叶绿素生物合成如何受到控制和调控有一个重要的了解。这项工作具有根本的重要性，因为它可以提供一种潜在的方法来提高植物的光合作用产量，特别是在胁迫条件下。

项目成果

Ultrafast catalytic processes and conformational changes in the light-driven enzyme protochlorophyllide oxidoreductase (POR).

• DOI: 10.1042/bst0370387
• 发表时间: 2009-04
• 期刊: Biochemical Society transactions
• 影响因子: 3.9
• 作者: O. Sytina;D. Heyes;C. N. Hunter;Marie Louise Groot-Marie Louise-Groot-2252530298