Directed Evolution of Photosystem Chemistry

光合作用对于生命进化的重要性怎么强调都不为过。它代表着改变地球并为复杂生命的兴起铺平道路的关键创新之一。今天，改善光合作用以提高作物产量和生产具有商业价值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，必须改变光合作用。研究光合作用的进化就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。对光合作用演化的研究可以为其改变、优化或改进的潜力提供相关的洞察。例如，我的研究表明，在地质年代的几个场合，氧气光合作用的化学成分被迅速和根本地优化，以匹配具有非常非典型光条件的环境，例如在200米深的开阔海域或叠层石中发现的环境。这表明这个过程的可塑性和适应性的潜力远远超出了目前人们的认识。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，从实验上证明控制和有目的地改变光合作用的化学是可能的。定向进化是一种非常通用的方法，它通过利用进化来改变给定酶的特征或活性。它可以简单地通过使有机体在有利于所需特征的条件下进行反复选择来完成，可以通过涡轮增压突变率来增强它，它可以集中在单个感兴趣的基因上，并可以与另一种称为祖先序列重建(ASR)的方法相结合。ASR是一种进化方法，通常用于计算酶的最可能的祖先状态。然后，可以使用商业上可用的服务来制造祖先酶基因，并用于在试管中研究祖先酶的性质。ASR的一个有趣的结果是，祖先的酶显示出优越的稳定性和功能灵活性。这些特性使ASR和定向进化的结合成为一种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计划，该计划利用ASR重建光系统II的祖先状态。光系统是大自然的太阳能电池，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。他们这样做已经有数十亿年了。光系统II利用光将水分解成氧、质子，并产生电流。这是氧气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“冰冻的新陈代谢事故”。一个概念的引入，意味着这些系统已经达到最优性能的最大水平，因此进化能力有限：换句话说，人们认为它们不能以任何有用的方式进行更改。然而，这一观点与我自己的工作相矛盾，相反，我的工作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，使用定向进化可以以任何理想的方式改变和控制光系统的功能。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，给出一组适当的选择压力。我们将为光系统化学的控制和优化提供工具和分子蓝图，以满足未来潜在的分子应用。

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.