Molecular Basis for Controlled Transmembrane Electron Transfer

大多数生物可以通过呼吸或呼吸产生能量。虽然像人类这样的生物体只能呼吸氧气，但细菌更灵活，可以呼吸各种各样的分子，包括硝酸盐，硫酸盐和不同的金属氧化物。在呼吸过程中，细菌分解其核心中的不同碳化合物，并释放电子。然后这些电子在一个被称为还原的过程中与目标分子结合。大多数在呼吸过程中被还原的分子都很小，可以很容易地进入细胞，但是有些细菌能够进行一种称为矿物呼吸的过程，字面意思是“呼吸岩石”，其中电子被用来还原不溶性金属。这是一个挑战，因为细菌必须安全地将电子移出细胞并进入矿物质;这一过程需要通过绝缘的外细胞膜进行电子传输。矿物呼吸过程是最古老的呼吸形式之一，改变了环境中许多金属的可用性，从必需元素铁和锰到毒性极强的铀和砷。这些细菌有效地控制了底土和地下水中这些金属的含量，因此了解它们的工作原理是环境修复的重要一步。这些过程也被证明在微生物燃料电池的开发中是有用的，在微生物燃料电池中，废物可以被分解，释放的电子可以用来发电或合成有用的产品，如苛性钠或乙醇。我们最近确定了这些细菌将电子从细菌中移出的方式之一：由三种不同蛋白质成分组成的生物导线。两种称为细胞色素的蛋白质，含有10个铁原子，每个铁原子都包含在一个称为血红素的辅因子中。一种细胞色素存在于细胞表面，而另一种存在于细胞内部。第三种蛋白质在细胞表面的膜中形成一个中空管，两个细胞色素的尖端从相对的两端插入该管并在中间相遇，允许电子直接在细胞色素之间移动并产生分子线。电子从细胞内部到细胞表面的运动是这些细菌的定义，对于我们理解如何利用这些细菌至关重要。该项目旨在了解这些生物导线如何在膜中发挥作用，以将电子移动到不同的矿物和电极中。我们将讨论的这个过程的一个基本方面是确定细胞色素是否专门针对不同的矿物质，或者它们是否只是将电子释放到附近的任何东西中。我们还将发现当跨膜的两个细胞色素断开时会发生什么;电子是否仍然可以移动出去，或者电线是否以某种方式关闭。这项研究将使用许多技术，包括东安格利亚大学专门为研究这些系统开发的一种新方法。这包括将复合物插入人造膜中，并测量电子在膜两侧的运动。我们还将发现不同类型的细胞色素如何相互作用，它们是否聚集在一起形成带电区域或分散在细胞表面，使用特殊的化学标记，当靠近时会发生变化。最后，我们将获得组分细胞色素以及整个复合物的结构。这项研究的结果将是对这种分子线最重要特性的理解，这可能导致其在各种生物修复和生物技术作用中的利用。

Most organisms can generate energy through respiration, or breathing. While organisms such as humans are restricted to breathing oxygen, bacteria are much more flexible and can breathe a broad variety of molecules, including nitrates, sulfates and different metal oxides. During respiration, the bacteria break down different carbon compounds in their cores, and electrons are released. These electrons are then combined with a target molecule in a process known as reduction. Most of the molecules reduced during respiration are small and can easily move into the cell, however some bacteria are capable of a process known as mineral respiration, literally 'breathing rock', where the electrons are used to reduce insoluble metals. This poses a challenge because the bacteria have to safely move the electrons out of the cell and into the mineral; a process that requires electron transport through the insulating outer cell membrane. The process of mineral respiration is one of the oldest forms of respiration and alters the availability of many metals in the environment, from the essential elements iron and manganese to the extremely toxic uranium and arsenic. The levels of these metals in the subsoil and groundwater are effectively controlled by these bacteria, so understanding how they work is an important step in environmental remediation. These processes are also proving useful in the development of microbial fuel cells, where waste material could be broken down and the released electrons used either to produce electricity or to synthesis useful products such as caustic soda or ethanol. We recently identified one of the ways in which these bacteria move electrons out of the bacteria: a biological wire made of three different protein components. Two proteins called cytochromes that contain ten iron atoms which are each held in a cofactor know as a haem. One cytochrome is found on the surface of the cell, while the other is found on the inside. The third protein forms a hollow tube in the membrane at the surface of the cell and the tips of the two cytochromes insert into this tube from opposite ends and meet in the middle, allowing electrons to move directly between the cytochromes and generating a molecular wire. The movement of electrons from the inside of the cell to the cell surface is what defines these bacteria and is essential to our understanding of how these bacteria can be utilised. This project aims to understand how these biological wires function in the membrane to move electrons across and into different minerals and electrodes. One fundamental aspect of this process that we will address is to identify whether the cytochromes are specifically tailored to different minerals, or if they simply discharge electrons into whatever is nearby. We will also find out what happens when the two cytochromes held across the membrane disconnect; whether electrons can still move out, or if the wire is somehow closed off. This research will use a number of techniques, including a novel method developed at the University of East Anglia specifically for studying these systems. This involves inserting the complex into an artificial membrane and measuring the movement of electrons across the two sides of the membrane. We will also find out how the different types of cytochromes interact with each other, whether they cluster together to form charged areas or spread across the cell surface, using special chemical labels that change when brought close together. Finally we will obtain structures of the component cytochromes as well as the entire complex. The outcome of this research will be an understanding of the most important properties of this molecular wire, which could lead to its utilisation in a variety of bioremediative and biotechnological roles.