Dynamics of Electron and Proton Transfer Chemistry in Copper and Hybrid Copper-Haem Enzymes

化学过程中有效的电子和质子转移的机制，以催化化学反应和实现必要的生化功能，仍然不完全清楚。这一建议结合了最先进的实验和高性能计算方法来解决这些问题，开发了创新的方法，重点是执行基础化学的蛋白质，作为全球氮循环的一部分，这些化学对环境很重要。新的实验方法包括快速室温X射线结晶学和单晶光谱学，而理论方法将是量子力学、分子力学和分子动力学的混合，并在最先进的并行处理计算机系统上进行计算。亚硝酸铜还原酶是重要的环境蛋白质，在反硝化过程中进行化学转化，将亚硝酸盐(NO2)转化为一氧化氮(NO)，这是生物‘氮循环’的关键步骤，氮气从土壤返回大气。我们将首先在无铬杆菌的一种酶中研究这一过程。它需要NO2与一个铜原子结合，并通过涉及第二个铜原子和电子以及质子转移到活性中心的机制将其还原为NO。这通常还涉及亚硝酸盐还原酶和细胞色素(电子供体)伙伴蛋白之间形成通常短暂的复合体，使化学研究变得困难。最近发现了一种新的亚硝酸还原酶，它含有一个“系留”的细胞色素结构域。这种来自Ralstonia Picketti的蛋白质是一种‘自含式电子转移’系统，这种特殊而罕见的结构消除了对瞬时蛋白质-蛋白质复合体的需要，为我们提供了一个独特的机会来详细研究这种基本的催化过程，即电子转移、质子转移、NO2传递和结合以及金属氧化态。我们的计划的结果将对任何涉及受控的电子和质子转移反应的化学过程具有广泛的相关性，这些过程在自然界中普遍存在，对于未来开发高效的仿生化合物或工业应用的合成酶和酶激发的催化剂至关重要。

The mechanisms of effective electron and proton transfer in chemical processes, to catalyse chemical reactions and enable essential biochemical functions, are still not fully understood. This proposal combines state of the art experimental and high performance computational methods to address these questions, developing innovative approaches with a focus on proteins that perform fundamental chemistry that is important to the environment as part of the global nitrogen cycle. New experimental methods include rapid room temperature X-ray crystallography and single crystal spectroscopies, while the theoretical approach will be a mixture of quantum mechanics, molecular mechanics and molecular dynamics, with the calculations performed on state of the art parallel processing computer systems.Copper nitrite reductases are important environmental proteins that carry out the chemistry to convert nitrite (NO2) to nitric oxide (NO) during the process of denitrification, a key step of the biological 'nitrogen cycle' whereby nitrogen gas is returned from the soil to the atmosphere. We will first study this process in an enzyme from Achromobacter cycloclastes. It requires binding of NO2 to a Cu atom and its reduction to NO via mechanisms involving a second Cu atom and electron and proton transfer to the 'active site'. This also normally involves the formation of a normally transient complex between the nitrite reductase and a cytochrome (electron donor) partner protein, making the chemistry difficult to study. Recently a new nitrite reductase has been discovered that contains a 'tethered' cytochrome domain. This protein, from Ralstonia picketti, acts as a 'self-contained electron transfer' system, an unusual and rare structure that negates the need for a transient protein-protein complex and which provides us with the unique opportunity to fully study such a fundamental catalytic process in detail, ie electron transfer, proton transfer, NO2 delivery and binding, as well as the metal oxidation states.The outcomes of our programme will be of broad relevance to any chemistry involving controlled electron and proton transfer reactions, processes that are ubiquitous in nature, and essential for future development of efficient biomimetic compounds or synthetic enzymes & enzyme-inspired catalysts for industrial applications.