Decreasing the oxygenase activity of Rubisco: a synthetic biology approach

光合作用是植物利用来自阳光的能量将大气中的二氧化碳转化为有机物质（生物质）的过程。光合作用为植物生长、作物产量和地球上所有生命提供动力。光合作用的第一步是将二氧化碳与含有5个碳原子的糖结合，形成两个糖分子，每个糖分子含有3个碳（C3）原子，这一过程称为二氧化碳固定。C3糖然后结合联合收割机以再生5碳受体并且还形成葡萄糖。葡萄糖被用作合成植物中所有其他分子的原料。植物中的化学反应，如光合作用的第一步，只有在被称为酶的蛋白质加速的情况下才能足够快地发生。Rubisco是加速二氧化碳固定的酶。不幸的是，这种酶具有内在的低效性。它是缓慢的，所以植物需要花费大量的能量来生产它。它还具有副反应，其中氧气与二氧化碳竞争与5C受体反应。这种副反应（称为加氧酶反应）的结果是形成较少的C3产物，光合作用速率比可能的要慢。一些藻类和植物已经发展出复杂的机制来增加Rubisco附近的二氧化碳浓度，从而降低加氧酶活性并提高光合作用的效率。不幸的是，我们的许多主要作物（如水稻，小麦，马铃薯和豆类）没有这种机制，各种方法来降低其加氧酶活性正在深入研究。为了促进这一努力，我们提出了一个试点研究，以评估物理连接Rubisco的另一种酶（碳酸酐酶，CA），在适当的条件下，可以提供高浓度的二氧化碳Rubisco和减少浪费的加氧酶活性的潜力。为了实现这一目标，我们建议通过工程细菌集胞藻来重新配置光合作用的二氧化碳固定步骤。我们将准备一个合成基因，当引入集胞藻时，它将导致它产生一个蛋白质支架，可以结合Rubisco和CA。修饰的菌株还将含有Rubisco和CA的形式，这些形式已经被改造成具有允许它们结合到支架蛋白的标签。这种工程生物将使我们能够测试的建议，密切接近的Rubisco和CA增加光合作用的效率，通过减少“浪费”的加氧酶活性。

Photosynthesis is the process whereby plants convert atmospheric carbon dioxide to organic matter (biomass) using energy from sunlight. Photosynthesis powers plant growth, crop productivity and all life on earth. The first step in photosynthesis combines carbon dioxide with a sugar containing 5 carbon atoms to make two sugar molecules each containing 3 carbon (C3) atoms in a process called carbon dioxide fixation. The C3 sugars then combine to regenerate the 5 carbon accceptor and also to form glucose. Glucose is used as the feedstock to synthesise all other molecules in the plant. Chemical reactions in plants, such as the first step in photosynthesis, only happen quickly enough if they are speeded up by proteins known as enzymes. Rubisco is the enzyme that speeds up carbon dioxide fixation. Unfortunately this enzyme has built-in inefficiencies. It is slow, so plants need to spend energy producing it in large quantities. It also has a side reaction in which oxygen competes with carbon dioxide to react with the 5C acceptor. The consequence of this side reaction (known as the oxygenase reaction) is that less C3 product is formed and photosynthesis rate is slower than it could be. Some algae and plants have developed elaborate mechanisms to increase the concentration of carbon dioxide near Rubisco, thereby decreasing oxygenase activity and increasing the efficiency of photosynthesis. Unfortunately, many of our major crops (e.g. rice, wheat, potatoes and pulses) do not have this mechanism and various approaches to reducing their oxygenase activity are being intensively investigated. To contribute to this effort, we are proposing a pilot study to assess the potential of physically linking Rubisco to another enzyme (carbonic anhydrase, CA) which, under the right conditions, could deliver a high concentration of carbon dioxide to Rubisco and reduce the wasteful oxygenase activity. To achieve this aim we propose to reconfigure the carbon dioxide fixing step of photosynthesis by engineering the bacterium Synechocystis. We will prepare a synthetic gene which, when introduced into Synechocystis will cause it to produce a protein scaffold that can bind both Rubisco and CA. The modified strain will also contain forms of Rubisco and CA that have been engineered with tags that allow them to bind to the scaffold protein. This engineered organism will allow us to test the proposal that close proximity of Rubisco and CA increases the efficiency of photosynthesis by decreasing the "wasteful" oxygenase activity.