Iron mobilisation in the bacterial cell

几乎所有的生物体都依赖铁来生存。铁是生命的关键元素，因为它在地壳中的丰度及其有用的化学和物理性质-例如，它非常善于转移电子，并激活氧气与一系列基质反应。这两个过程都是呼吸作用的关键过程，也就是将储存在食物中的能量转化为可用形式的过程，从而说明了为什么生物体依赖于这种金属。尽管铁的丰富和有用的特性，但它给生物体带来了两个问题。首先，自从地球大气中的氧含量开始增加以来，铁主要以氧化和高度不溶性的矿物形式存在，不容易被生物体利用。因此，铁通常是生长的限制性营养素，其可用性可以例如决定细菌病原体是否可以成功地定殖其宿主。其次，使铁如此有用的化学物质意味着它对细胞也有很高的毒性。为了解决这些问题，一系列智能机制已经进化出来，使生物体能够从环境中吸收铁，当发现铁超过即时需求时将其储存起来，并将其以无毒形式保持在细胞内。后两者是通过铁储存分子实现的，这些分子存在于从最简单到最复杂的所有细胞类型中。铁储存蛋白属于铁蛋白超家族，具有不寻常的结构，由24个亚基组成，排列形成一个大的球形蛋白质壳，围绕着一个中心空腔，其中可以储存多达4，500个铁原子。细菌是最简单的生物体，通常含有两种不同类型的铁蛋白：一种铁蛋白（Ftn），与哺乳动物中发现的原型铁蛋白非常相似，另一种细菌铁蛋白（BFR），是迄今为止仅在细菌中发现的更远的含血红素蛋白质。我们和其他人已经在模式细菌E.因此，我们可以更详细地了解它们的合成是如何被控制的，以及它们是如何储存大量铁的。在环境缺铁的时候，细菌和其他生物会动员它们的铁储备来弥补外部铁的缺乏。然而，人们对铁是如何从细菌或更复杂的生物体（如哺乳动物）中释放的知之甚少。我们和其他人已经确定了一个小的电子转移蛋白，Bfd，我们建议发挥关键作用，铁动员从BFR。我们现在希望检验我们的假设，并首次在任何生物体中证实铁从铁储存蛋白中动员的过程。这里提出的研究独特地汇集了我们在铁代谢生理学（在阅读）和铁储存蛋白的生物化学（在UEA）方面的专业知识，以解决铁代谢的这一主要遗留问题。使用真正的多学科方法，采用广泛的遗传学，生物化学和生物分析方法，我们将详细研究铁动员从BFR和Ftn在E。大肠杆菌中，Bfd及其它相关因子在此过程中所起的作用。我们还将阐明BFR和Ftn在铁储存过程中各自的作用（目前还不清楚为什么E。大肠杆菌和其他细菌拥有两种这样不同的铁储存蛋白），并试图鉴定与这些蛋白相互作用的其他细胞因子。这项工作将对我们理解细菌如何利用先前储存的铁进行合成过程产生重大影响。与BB/D 002435/1连接。

Nearly all organisms depend on iron for their existence. Iron is a key element for life because of its abundance in the earths crust and its useful chemical and physical properties - e.g. it is very good at transferring electrons, and activating oxygen for reaction with a range of substrates. Both of these are key processes in respiration - the means by which energy stored in foods is converted into a useable form - thus illustrating why organisms are dependent on this metal. Despite its abundance and useful properties, iron presents organisms with two problems. Firstly, ever since the oxygen levels in the earth's atmosphere began to increase, iron has been present largely in an oxidised and highly insoluble mineral form that is not readily available for utilisation by organisms. As a consequence, iron is often a limiting nutrient for growth and its availability can, for example, determine whether or not a bacterial pathogen can successfully colonise its host. Secondly, the chemistry that makes iron so useful means that it can also be highly toxic to the cell. To counter these problems, a whole range of smart mechanisms have evolved that enable organisms to scavenge iron from their environment, to stock pile it when it is found in excess of immediate requirements, and to maintain it within the cell in a non-toxic form. The latter two are achieved by iron-storage molecules that are found in all cell types from the simplest to the most complex. Iron-storage proteins belong to the ferritin super-family and have unusual structures consisting of 24 subunits arranged to form a large, spherical protein shell surrounding a central cavity where up to 4,500 iron atoms can be stored. Bacteria, which are the simplest of organisms, often contain two different types of ferritin: a ferritin (Ftn) which resembles closely the archetypal ferritins found in mammals, and a bacterioferritin (BFR) which are more distantly related heme-containing proteins, so far found only in bacteria. We and others have studied these iron-storage proteins in the model bacterium E. coli, and so understand in some detail how their synthesis is controlled and how they are able to store large quantities of iron. In times of environmental iron deficiency, bacteria and other organisms mobilise their iron stores to compensate for the lack of external iron. However, very little is known about how iron is released from iron stores, either in bacteria or in more complex organisms such as mammals. We and others have identified a small electron transfer protein, Bfd, which we propose plays a key role in iron mobilisation from BFR. We now wish to test our hypothesis and to characterise, for the first time in any organism, the processes involved in iron mobilisation from iron-storage proteins. The research proposed here uniquely brings together our expertises in the physiology of iron metabolism (at Reading) and the biochemistry of iron-storage proteins (at UEA) in order to tackle this major remaining question of iron metabolism. Using a truly multi-disciplinary approach employing a wide range of genetic, biochemical and bioanalytical methods, we will study in detail iron mobilisation from BFR and Ftn in E. coli, and the role played by Bfd and other relevant factors in this process. We will also clarify the respective roles of BFR and Ftn in the iron-storage process (it is unclear why E. coli and other bacteria possess two such distinct iron-storage proteins) and seek to identify other cellular factors that interact with these proteins. This work will have a major impact on our understanding of how bacteria utilise previously stored iron for synthetic processes. Joint with BB/D002435/1.