Artificial metalloproteins: photochemical and electrochemical approaches for understanding mechanism and catalysis

加速气候变化要求开发能够获得可再生化学燃料和原料的新技术。尽管目前正在寻求许多方法，但使用蛋白质的催化仍然是一种未实现的资源，特别是对于氧化还原转化(例如，二氧化碳到甲醇)。氧化还原酶是催化的理想候选者，因为它们自然地对复杂转换所需的高能电子进行精细控制。我们对多步电子转移反应的理解以及蛋白质设计的最新进展，为人工修饰蛋白质催化剂的研究开辟了新的途径。为此，我的生物无机化学研究计划的一个长期目标是开发新一代生物催化剂，能够与“最先进的”工业方法竞争。此外，随着我们设计、合成和研究新的基于蛋白质的催化剂，我们还将开发一套全面的衡量标准，可用于评估和改善氧化还原功能。我们将解决有关电子如何在人造蛋白质中移动以及我们如何最好地利用生物氧化还原机制进行基本化学转化的基本问题。未来5年，这项研究将集中于以下三个短期目标：(1)展示新型蛋白质+氧化铟锡电极的光电催化；(2)利用工程血红素蛋白选择性氧化有机生物聚合物；(3)修饰金属蛋白以用于可再生能源氧化还原催化剂。这三个相辅相成的研究目标解决了大规模使用酶的关键障碍：构建设备，优化蛋白质催化，阐明新的靶向催化剂的设计标准。在目标1中，我们将建立将功能蛋白固定在电极表面的方法(设备开发)。这为电化学和光催化开辟了道路。在目标2中，我们重点关注对容易获得的蛋白质细胞色素c过氧化物酶的仔细修饰，以诱导新的氧化还原功能(催化剂优化)。保守和系统的方法将提供关于结构-功能关系的具体信息。理想情况下，这些新系统将服从通过目标1制定的固定化战略。最后，我们在目标3方面的工作将采取更雄心勃勃的策略(设计新催化剂)。从非常稳定、耐热的金属蛋白质开始，我们将产生具有暴露的(配位不饱和)金属位点的蛋白质。氢键和空间位阻使蛋白质成为特殊的“配体”，支持不寻常的配位几何构型，并赋予第一排过渡金属独特的反应性。然而，很少有研究利用这种控制来构建具有反应活性的蛋白质，以反映或改进小分子催化剂的活性。我们将生产和广泛表征人造蛋白质以建立设计元素，然后调查金属位置对底物的反应性(例如，将质子还原为二氢)。综上所述，从这项研究计划中获得的知识将提供新的方法，以满足我们对可再生化学催化的日益增长的需求，因为我们正在加速从化石燃料向全球的过渡。我们的工作范围从光电化学器件的开发(目标1)到蛋白质氧化还原催化剂的设计和优化(目标2和3)。我的计划中的一系列项目将使使用人造蛋白质进行催化的新方法和新技术成为可能，同时为生物无机化学和催化领域的高素质人才的智力和专业发展提供丰硕的机会。

Accelerating climate change demands the development of new technologies that enable access to renewable chemical fuels and feedstocks. Despite the many approaches currently being pursued, catalysis using proteins remains an unrealized resource, especially for redox transformations (e.g., carbon dioxide to methanol). Redox enzymes are ideal candidates for catalysis because they naturally exert exquisite control over the energetic electrons required for complex transformations. Recent advances in our understanding of multistep electron transfer reactions, as well as protein design, open new avenues for investigations of artificially modified protein catalysts. To that end, a long-term goal of my bioinorganic chemistry research program is to develop a new generation of biocatalysts that can compete with “state-of-the-art” industrial approaches. Further, as we design, synthesize, and investigate new protein-based catalysts we will also develop a comprehensive set of metrics that can be used to assess and improve redox functions. We will address fundamental questions about how electrons move in artificial proteins and how we can best exploit biological redox machinery for essential chemical transformations. The proposed research will focus on the following three short-term objectives over the next 5 years: (1) to demonstrate photoelectrochemical catalysis by novel protein + indium tin oxide electrodes; (2) to selectively oxidize organic biopolymers with engineered heme proteins; and (3) to modify metalloproteins for renewable energy redox catalysis.These three complementary research objectives address key hurdles to using enzymes on large scales: constructing devices, optimizing protein catalysis, and elucidating design criteria for new, targeted catalysts. In Objective 1 we will establish methods for immobilizing functional proteins on electrode surfaces (device development). This opens the way for electrochemical- and photo-catalysis. In Objective 2 we focus on careful modifications to the easily obtained protein cytochrome c peroxidase to elicit new redox functions (catalyst optimization). A conservative and systematic approach will provide specific information about structure-function relationships. Ideally, these new systems will be amenable to immobilization strategies developed through Objective 1. Finally, our work on Objective 3 will take a more ambitious tact (designing new catalysts). Starting from very stable, heat tolerant metalloproteins, we will generate proteins with exposed (coordinatively unsaturated) metal sites. Hydrogen bonding and steric constraints make proteins exceptional “ligands” for supporting unusual coordination geometries and imparting unique reactivity upon first-row transition metals. However, few studies have taken advantage of this control to build proteins with reactivity that mirrors or improves upon that of small molecule catalysts. We will produce and extensively characterize artificial proteins to establish design elements, and then investigate the reactivity of the metal sites toward substrates (e.g., reduction of protons to dihydrogen).Taken together, the knowledge gained from this research program will provide new ways to approach our growing need for renewable chemical catalysis as we accelerate a global transition away from fossil fuels. Our work ranges from the development of photoelectrochemical devices (Objective 1) to design and optimization of protein redox catalysts (Objectives 2 and 3). The range of projects in my program will enable new approaches and technologies for catalysis using artificial proteins, while providing fruitful opportunities for the intellectual and professional development of highly qualified personnel in biological inorganic chemistry and catalysis.