Regulation of Bacterial Heme Metabolism

项目概要（描述） 血红素及其生物合成的调节对于正常细胞功能是重要的，并且有助于细胞的生长。 成功的细菌不同的环境，包括那些与致病和共生 与高等真核生物的相互作用。现在已知血红素是一种调节分子，可以让细胞感知 并适应环境线索以维持体内平衡。拟议工作的总体目标是 了解血红素如何介导基因表达的控制，重点是铁代谢， 将血红素的这种作用与其在细胞中的毒性相协调。 血红素生物合成途径的高潮是铁通过一个环插入到原卟啉环中。 铁螯合酶催化的反应。我们发现了一种叫做Irr（铁反应调节因子）的调节蛋白。 来自细菌慢生根瘤菌（Bradyrhizobium japonicum），其直接与亚铁螯合酶相互作用。这本小说 这一机制允许Irr在血红素合成位点局部地对血红素作出反应。IRR是条件稳定的 在铁限制下发挥功能，但以血红素依赖性方式响应铁而降解的蛋白质。IRR 最初被描述为血红素生物合成的调节剂，但新的证据表明，它是一个全球调节剂 铁依赖性基因因此，该提议的主要目标是解决假设B。日本 通过血红素的状态以Irr依赖的方式感知铁以调节铁稳态和代谢。 此外，Irr同源物在大多数变形菌中被发现，因此所提出的工作可作为模型 了解血红素和铁代谢的致病菌，实验上是不太容易处理的 而不是B。山茱萸 提出了三个具体目标。1.确定Irr识别靶基因的机制， 控制他们的表达。Irr强烈调节编码三价铁转运蛋白和许多其他铁转运蛋白的基因。 相关基因，是一个积极和消极的调节。我们对Irr的激活特别感兴趣 因为细菌铁转运阳性对照并不常见。2.阐明Irr感知的机制 血红素的状态。Irr与亚铁螯合酶相互作用，后者为Irr提供调节输入。我们将 表征这种相互作用的生化和遗传，并阐明随后的抑制和 Irr降解3.通过非Irr依赖性的铁离子通道阐明铁对血红素利用基因的调控 机制数据表明，血红素合成从头控制不同， 外生的我们将确定这种调节机制，并建立如何IR依赖和独立 新陈代谢是一体化的。

PROJECT SUMMARY (DESCRIPTION) Heme and the regulation of its biosynthesis are important for normal cell function, and contribute to the success of bacteria to diverse environments, including those associated with pathogenic and symbiotic interactions with higher eukaryotes. Heme is now known to be a regulatory molecule that allows cells to sense and adapt to environmental cues to maintain homeostasis. The broad objective of the proposed work is to understand how heme mediates the control of gene expression, with an emphasis on iron metabolism, and to reconcile this role for heme with its toxicity in cells. The heme biosynthetic pathway culminates with the insertion of iron into a protoporphyrin ring by a reaction catalyzed by ferrochelatase. We discovered a regulatory protein called Irr (iron response regulator) from the bacterium Bradyrhizobium japonicum that interacts directly with ferrochelatase. This novel mechanism allows Irr to respond to heme locally at the site of heme synthesis. Irr is a conditionally stable protein that functions under iron limitation, but degrades in response to iron in a heme-dependent manner. Irr was initially described as a regulator of heme biosynthesis, but new evidence reveals that it is a global regulator of iron-dependent genes. Thus, a major objective of this proposal is to address the hypothesis that B. japonicum senses iron through the status of heme in an Irr-dependent manner to regulate iron homeostasis and metabolism. Furthermore, Irr homologs are found in most ¿-Proteobacteria, and thus the proposed work serves as a model for understanding heme and iron metabolism in pathogenic bacteria that are experimentally much less tractable than B. japonicum. Three specific aims are proposed. 1. Determine the mechanism by which Irr recognizes target genes and controls their expression. Irr strongly regulates genes encoding ferric iron transporters and many other iron- related genes, and is both a positive and negative regulator. We are particularly interested in activation by Irr since positive control of bacterial iron transport is uncommon. 2. Elucidate the mechanism by which Irr senses the status of heme. Irr interacts with ferrochelatase, which provides the regulatory input to Irr. We will characterize this interaction both biochemically and genetically, and elucidate the subsequent inhibition and degradation of Irr. 3. Elucidate the regulation of heme utilization genes by iron by an Irr-independent mechanism. Data suggest that heme synthesized de novo is controlled differently than that acquired exogenously. We will identify this regulatory mechanism, and establish how Irr-dependent and -independent metabolism is integrated.