Functional characterization of Iron Regulator Sensor (IRS) proteins in plants

铁是我们食物中的一种必需矿物质。因此，儿童被鼓励吃富含铁的绿色蔬菜，如大力水手卡通片中广告的菠菜。植物食物是我们膳食铁的主要来源，它们直接从土壤中获得。植物在开采土壤中的铁方面效率极高，但它们所需的铁不会超过它们自身的需要。这是因为铁以其自由形式存在，具有极强的毒性。一旦铁进入细胞，它就会被伴侣蛋白结合，在细胞内安全地携带铁，然后立即将其结合到酶中，发挥催化剂的作用。一些铁也可以储存在特定的蛋白质或细胞隔间中。平衡铁的吸收、使用和储存被称为动态平衡。维持体内平衡的核心是铁传感器，它向基因表达的调节器发出信号，以改变转运蛋白(和其他铁稳态蛋白)的水平。在细菌、酵母和哺乳动物中都发现了铁传感器。然而，我们仍然不知道铁是如何在植物中感知的，也不知道哪些蛋白质起到铁传感器的作用。然而，我们知道铁稳态基因在植物中的表达受到非常严格的调控，因此肯定有一个非常敏感的铁传感器。对缺铁条件下生长的植物的基因表达网络进行了深入的分析，发现了三种候选蛋白质作为铁传感器。这些蛋白质在序列上是相关的，但存在于不同的组织中。使它们成为很好的候选者的是它们在铁调节网络中的调控模式，它们与哺乳动物中的铁感应蛋白的相似性，以及几个铁结合蛋白结构域。在拟议的项目中，我们想要确认这些名为IRS1、IRS2和BTS的蛋白质在铁稳态中的作用。首先，我们将测量铁与不同蛋白质结构域的结合，铁是以什么形式存在的，以及结合的强度有多大。传感器蛋白中的结合常数应该相对较弱。我们还将尝试并阐明这些蛋白质如何协调下游信号事件。它们可能会与其他蛋白质相互作用，我们将使用现有的方法来确定这些相互作用的伙伴。为了养活不断增长的世界人口，有人建议我们都应该少吃肉。然而，如果我们减少这种丰富的铁来源，这可能会导致缺铁性贫血，这在英国女孩和妇女中已经很常见，在发展中国家也很普遍。如果我们的饮食中含有丰富的绿色蔬菜和豆类，植物可以提供足够的铁。情况并不总是如此，因此增加小麦(面包)和土豆等主食中的铁含量将是有益的。要做到这一点，唯一的方法是欺骗工厂吸收比它需要的更多的铁，并实现巨大的铁存储容量。为此，我们需要首先找到铁传感器，这样我们才能改变它的灵敏度和信号能力。

Iron is an essential mineral in our food. Therefore children are encouraged to eat iron-rich green vegetables such as spinach advertised in Popeye cartoons. Plant foods are the primary source of our dietary iron which they obtain directly from the soil. Plants are extremely efficient at mining the soil for iron, but they will take up no more than they require for their own needs. This is because iron, in its free form, is extremely toxic. As soon as iron enters the cell, it is bound by chaperone proteins to carry iron safely around the cell and then immediately incorporate it in enzymes to function as catalysts. Some iron can also be stored in specific proteins or cell compartments. Balancing the uptake, use and storage of iron is called homeostasis. Central to maintaining homeostasis is an iron sensor, which signals to regulators of gene expression to alter the levels of transporters (and other iron homeostasis proteins). Iron sensors have been described in bacteria, in yeast and in mammals. However, we still do not know how iron is sensed in plants, or which proteins function as iron sensors. However, we do know that the expression of iron homeostasis genes is very tightly regulated in plants, so there must be a very sensitive Fe sensor.Extensive analyses of gene expression networks in plants grown under iron-deficient conditions has turned up three candidate proteins for the iron sensor. The proteins are related in sequence but are present in different tissues. What makes them good candidates is their pattern of regulation within the iron regulatory network, their similarity to an iron-sensing protein in mammals, and several iron binding protein domains. In the proposed project we would like to confirm the role of these proteins, named IRS1, IRS2 and BTS, in iron homeostasis. First, we will measure iron binding to the separate protein domains, what form the iron is in and how strong the binding is. A relatively weak binding constant is expected in sensor proteins. We will also try and elucidate how the proteins orchestrate downstream signalling events. They are likely to interact with other proteins, and we will use established methods to identify these interaction partners.To feed the growing world population, it has been suggested that we should all eat less meat. However, if we cut down on this rich source of iron, this could lead to iron deficiency anaemia, which is already common among girls and women in the UK and widespread in the developing world. Plants can provide enough iron if our diet is rich in green vegetables and pulses. This is not always the case, therefore it would be beneficial to increase the amount of iron in staple foods such as wheat (for bread) and potatoes. The only way to do this, is to trick the plant in taking up more iron than it needs, and enable a large iron storage capacity. For this, we need first find the iron sensor, so we can alter its sensitivity and signalling capacities.