Heme Scavenging and Uptake by Haemophilus ducreyi

描述(申请人提供)：尽管自然界中铁含量丰富，但人体内游离铁的浓度约为10-18M，其中大部分铁被隔离在宿主蛋白中，如转铁蛋白和血红蛋白(Hb)。为了克服铁缺乏，人类细菌病原体进化出了许多获取铁的机制。一种这样的机制是细胞表面受体的表达，该受体专用于宿主含血红素的蛋白。杜热性嗜血杆菌是性传播生殖器溃疡下巴疾病的病原体，它只表达一种毒力所需的清除铁的机制。这种铁清除蛋白是一种名为HgbA的Hb受体。HgbA属于外膜蛋白的一个大家族，它依赖于TonB，通过内膜的质子动力将能量连接到外膜中进行运输。尽管TonB依赖的受体在结构上相似，但从不同底物获得铁或血红素的机制似乎不同。此外，尽管大多数病原体表达从Hb中提取血红素的蛋白质，但到目前为止还没有确定Hb结合/运输蛋白的结构。关于杜氏梭子虫从血红蛋白中摄取血红素的具体情况，我们知之甚少。确定杜氏杆菌获得铁/血红素的机制可能会导致针对铁获得的新抗生素策略的开发，这可能会影响所有病原体，包括疾控中心定义为A类选择药物的病原体。我们的短期目标是确定HgbA如何与其底物Hb结合，如何从Hb中去除血红素，以及HgbA如何将血红素运输到周质。我们的长期目标是了解血红素从Hb中的吸收，使用H.ducreyi作为病原菌中从Hb中清除Hb的模型。利用细菌学和生物物理技术相结合的方法，我们将探索杜氏嗜血杆菌HgbA血红素受体的结构和功能。 与公共卫生相关：铁极其稀缺，因此细菌病原体已经开发出从人类宿主那里窃取铁的机制。这项提案描述了探索一种名为H.ducreyi的细菌如何结合并从血红蛋白中去除含铁分子血红素的实验。

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.