Heme Scavenging and Uptake by Haemophilus ducreyi

描述（由申请人提供）：虽然铁在自然界中是丰富的，但游离铁在人类宿主中的浓度约为10-18 M，其中大部分铁被隔离在宿主蛋白质如转铁蛋白和血红蛋白（Hb）中。为了克服铁缺乏，人类细菌病原体已经进化出许多获得铁的机制。一种这样的机制是表达对宿主含血红素蛋白质具有特异性的细胞表面受体。杜克雷嗜血杆菌是性传播生殖器溃疡疾病软下疳的病原体，它只表达一种毒力所需的铁清除机制。这种铁清除蛋白是一种称为HgbA的Hb受体。HgbA属于依赖于TonB的外膜蛋白的大家族，TonB通过内膜的质子动力将能量连接到外膜中运输。虽然TonB依赖性受体在结构上相似，但从不同底物获得铁或血红素的机制似乎不同。此外，没有Hb结合/转运蛋白的结构已被确定到目前为止，即使大多数病原体表达的蛋白质提取血红素从Hb。关于H. ducreyi。确定了H. ducreyi可能导致开发针对铁获取的新抗生素策略，这可能影响所有病原体，包括CDC定义为A类选择剂的病原体。我们的短期目标是确定HgbA如何能够结合其底物Hb，如何从Hb中去除血红素，以及HgbA如何将血红素转运到周质。我们的长期目标是利用H. ducreyi作为病原菌中血红素从Hb中清除的模型。利用细菌学和生物物理学技术相结合的方法，我们将探索来自H. ducreyi。 公共卫生相关性：铁是极其稀缺的，因此细菌病原体已经开发出从人类宿主中窃取铁的机制。这项提议描述了一种名为H. Ducreyi能够结合并从血红蛋白中除去含铁分子血红素。

DESCRIPTION (provided by applicant): Although iron is abundant in nature, the concentration of free iron is approximately 10-18 M in the human host, where the majority of iron is sequestered in host proteins such as transferrin and hemoglobin (Hb). To overcome iron scarcity, human bacterial pathogens have evolved numerous mechanisms to acquire iron. One such mechanism is the expression of cell surface receptors specific for host heme-containing proteins. Haemophilus ducreyi, the causative agent of the sexually transmitted genital ulcer disease chancroid, expresses only one iron-scavenging mechanism required for virulence. This iron-scavenging protein is a Hb receptor termed HgbA. HgbA belongs to a large family of outer membrane proteins that are dependent on TonB that link energy via the proton-motive force of the inner membrane to transport in the outer membrane. Although TonB-dependent receptors are structurally similar, the mechanisms to acquire iron or heme from different substrates appear to be different. Furthermore, no structures of Hb-binding/transport proteins have been determined so far, even though most pathogens express proteins to extract heme from Hb. Very little is known specifically about heme uptake from Hb in H. ducreyi. Determining the mechanism of iron/heme acquisition of H. ducreyi may lead to the development of new antibiotic strategies targeting iron acquisition, which may impact all pathogens, including those defined by the CDC as category A select agents. Our short-term goal is to determine how HgbA is able to bind its substrate Hb, how it removes heme from Hb, and how HgbA transports heme to the periplasm. Our long-term goal is to understand heme uptake from Hb using H. ducreyi as a model of heme scavenging from Hb in pathogenic bacteria. Using a combination of bacteriology and biophysical techniques, we will explore the structure and function of the HgbA heme receptor from H. ducreyi. PUBLIC HEALTH RELEVANCE: Iron is extremely scarce and so bacterial pathogens have developed mechanisms to steal iron from the human host. This proposal describes experiments to explore how a bacterium called H. ducreyi, is able to bind and remove the iron containing molecule heme from hemoglobin.