Directed Evolution of Photosystem Chemistry

光合作用对生命进化的重要性怎么强调都不为过。它代表了改变地球的关键创新之一，并为复杂生命的兴起铺平了道路。如今，改善光合作用以增强作物和生产具有商业利益的化合物已成为光合作用研究的重大挑战之一，要改善光合作用，就必须改变光合作用。光合作用进化的研究是研究光合作用如何随着时间的推移而变化，这一直是我研究的重点。对光合作用进化的研究可以提供有关其变化、优化或改进潜力的相关见解。例如，我的研究表明，在地质时期的几个场合，含氧光合作用的化学反应迅速而彻底地优化，以适应具有非常非典型光照条件的环境，例如在200米深的开阔海洋沃茨或层间层中发现的环境。这表明该过程具有一定程度的可塑性和适应性潜力，远远超出了目前所认识的。我想将我对光合作用进化的研究与定向进化方法联系起来，以实验证明控制和有目的地改变光合作用的化学性质是可能的。定向进化是一种非常通用的方法，用于改变给定酶的特性或活性，利用进化论它可以简单地通过在有利于所需性状的条件下使生物体经历重复的选择循环来完成，它可以通过涡轮增压突变率来增强，它可以集中在单个感兴趣的基因上，并且它可以与另一种称为祖先序列重建（ASR）的方法相结合ASR是一种通常用于计算酶最可能的祖先状态的进化方法。然后可以使用商业上可获得的服务来制备祖先酶基因，并用于研究试管中祖先酶的特性。ASR的一个有趣的结果是，祖先酶显示出上级的稳定性和功能灵活性。这些特性使得ASR和定向进化的结合成为一个强大的生物技术工具。我目前领导着一个关于光合作用分子进化的研究项目，该项目利用ASR重建光系统II的祖先状态。光系统是自然界的太阳能电池，它们通过将光转化为有用的化学能来为地球上的生命提供动力。它们已经这样做了数十亿年。光系统II利用光将水分解成氧气、质子，并产生电流。这是光合作用的标志性化学反应，光系统是非常复杂的分子机器。这种复杂性意味着它们的进化非常缓慢。人们通常认为它们是作为“冷冻代谢事故”存在的。引入这个概念是为了暗示这些系统已经达到了最佳性能的最大水平，因此具有有限的可进化性：换句话说，人们认为它们不能以任何有用的方式进行改变。然而，我的研究却与这种观点相矛盾，我的研究表明，光系统具有巨大的自然适应潜力。我的研究小组旨在证明，通过使用定向进化，光系统的功能可以以任何理想的方式改变和控制。我们将证明，光系统的功能可以被优化到任何特定的条件下给出一个适当的选择性压力。我们将为未来潜在的分子应用提供控制和优化光系统化学的工具和分子蓝图。

The importance of photosynthesis for the evolution of life can hardly be overemphasised. It represents one of the key innovations that transformed Earth and paved the way for the rise of complex life.Today, the improvement of photosynthesis to enhance crops and the production of compounds of commercial interest has become one of the grand challenges of photosynthesis research.To improve photosynthesis, it is necessary to change photosynthesis. The study of the evolution of photosynthesis is the study of how photosynthesis has changed through time, which has been the focus of my research. The study of the evolution of photosynthesis can provide relevant insight on its potential for change, optimisation, or improvement.For example, my research has shown that in several occasions through geological time, the chemistry of oxygenic photosynthesis was rapidly and radically optimised to match environments with very atypical light conditions such as those found at 200 meter-deep open ocean waters or within stromatolites. This indicated that the process has a level of plasticity and potential for adaptability well beyond what is currently recognised.I want to link my research on the evolution of photosynthesis with Directed Evolution methods to experimentally prove that it is possible to control and purposefully change the chemistry of photosynthesis.Directed Evolution is an extremely versatile method that is used to change the traits or the activity of a given enzyme by exploiting evolution. It can be done simply by subjecting an organism through repeated cycles of selection under the conditions that favour the desired traits, it can be enhanced by turbocharging mutational rates, it can be focused on a single gene of interest, and it can be combined with another method called Ancestral Sequence Reconstruction (ASR).ASR is an evolutionary method commonly used to compute the most likely ancestral state of an enzyme. The ancestral enzyme gene can then be made using commercially available services and used to study the properties of the ancestral enzyme in the test tube. An interesting outcome of ASR is that the ancestral enzymes show superior stability and functional flexibility. These properties have made the combination of ASR and Directed Evolution a powerful biotechnological tool.I currently lead a research programme on the molecular evolution of photosynthesis and this employs ASR to reconstruct the ancestral states of Photosystem II.Photosystems are nature's solar cells and they power life on Earth by converting light into useful chemical energy. They have done so for billions of years. Photosystem II uses light to decompose water into oxygen, protons, and to generate an electric current. This is the hallmark chemical reaction of oxygenic photosynthesis.The photosystems are very complex molecular machines. This complexity means that they evolve very slowly. It is often believed that they exist as "frozen metabolic accidents". A concept that was introduced to imply that these systems have reached a maximum level of optimal performance and therefore have limited evolvability: in other words, it is thought that they cannot be changed in any way that is useful. This view is however contradicted by my own work, which instead suggests the photosystems have tremendous natural adaptability potential.My research group aims to demonstrate that the function of the photosystems can be changed and controlled in any desirable way with the use of Directed Evolution. We will demonstrate that the function of the photosystems can be optimised to any particular condition given an appropriate set of selective pressures. We will provide tools and a molecular blueprint for the control and optimisation of photosystem chemistry for potential future molecular applications.