Selective Gene Regulation by Manganese and Iron in Bacillus subtilis

枯草芽孢杆菌为分析基因调控的复杂性提供了一种遗传特征良好的模式生物。先前的工作已经定义了两组受金属离子可用性调节的基因：(i)参与铁摄取的基因被Fur同源物抑制；（ii）参与氧化应激保护的基因在锰、铁或某些其他二价金属离子存在时被一种名为PerR的蛋白质抑制。本项目将对枯草芽孢杆菌皮毛蛋白进行鉴定和表征。furA和furB基因是枯草芽孢杆菌基因组计划的一部分，它们编码的蛋白质与金属活化抑制蛋白Fur家族同源，可能是Fur和perR基因的候选基因。将采用遗传方法确定影响Fur和PerR调控的调控因子。Fur的生化特性将揭示其DNA的分子基础和金属结合选择性。Fur调控子的铁特异性可能是由于这种金属调节蛋白能够区分化学上相关的过渡金属。这与DtxR和e.c coli Fur相对广泛的金属选择性形成对比。过氧化调节子的广泛金属选择性是由PerR赋予的，PerR被假设为一种相对非特异性的金属结合蛋白，作为同时存在氧化还原活性金属离子和过氧化氢的分子传感器。金属离子是生命所需的许多化学转化必不可少的辅助因子，包括呼吸、DNA复制和转录过程。特别是，铁在氧气存在和接近中性pH值的情况下溶解度极低，并且经常限制细菌在环境中的生长，在病原生物的情况下，在宿主中。细菌已经进化出一种高度复杂的策略，通过合成、排泄和再吸附铁特异性有机螯合剂，即铁载体，从环境中获取铁。这个过程是高度调控的，因为正如低铁会限制生长一样，细胞内铁的过量会导致有害的化学反应，破坏细胞膜和DNA。这些有害的副反应经常涉及活性氧。有一种新兴的认识，即金属离子稳态经常与设计用于处理活性氧的系统协调。本研究旨在探讨革兰氏阳性土壤微生物枯草芽孢杆菌（Bacillus subtilis）铁稳态的遗传机制，以及铁稳态与细胞抗氧化损伤的关系。

Helmann 9630411 Bacillus subtilis provides a genetically well-characterized model organism ideal for analyzing the complexities of gene regulation. Previous work has defined two sets of genes regulated by metal ion availability: (i) genes involved in iron uptake which are repressed by a Fur homolog and (ii) genes involved in protection against oxidative stress which are repressed by a protein designated PerR in the presence of manganese, iron or certain other divalent metal ions. In this project, the B.subtilis Fur protein will be identified and characterized. The furA and furB genes, identified as part of the B. subtilis genome project, encode proteins homologous to the Fur family of metal-activated repressor proteins and are likely candidates for the fur and perR genes. A genetic approach will be pursued to identify regulatory factors influencing the Fur and PerR regulons. Biochemical characterization of Fur will reveal the molecular basis of its DNA and metal-binding selectivity. The iron specificity of the Fur regulon presumably results from an ability of this metalloregulatory protein to discriminate against chemically related transition metals. This contrasts with the relatively broad metal selectivity of DtxR and E.coli Fur. The broad metal selectivity of the peroxide regulon is imparted by PerR, which is hypothesized to be a relatively non-specific metal-binding protein which acts as a molecular sensor of the simultaneous presence of redox active metal ions and hydrogen peroxide. Metal ions are essential cofactors for many of the chemical transformations required for life, including the processes of respiration, DNA replication, and transcription. In particular, iron is of vanishingly low solubility in the presence of oxygen and near neutral pH and frequently limits the growth of bacteria both in the environment and, in the case of pathogenic organisms, in the host. Bacteria have evolved a highly sophisticated strategy to obtain iron from the environment by the synthesis, excretion, and readsorption of iron specific organic chelators known as siderophores. This process is highly regulated, since just as low iron can limit growth, an overabundance of intracellular iron can lead to deleterious chemical reactions that damage membranes and DNA. These harmful side reactions frequently involve reactive oxygen species. There is an emerging realization that metal ion homeostasis is frequently coordinated with systems designed to handle reactive oxygen species. This research explores the genetic mechanisms which control iron homeostasis in Bacillus subtilis, a gram positive soil micoorganism, and the relationship between iron homeostasis and cellular defenses against oxidative damage.