Bacterial Response to Singlet Oxygen

描述（由申请人提供）：分子氧（O2）对地球上的生命至关重要;它是产氧光合作用的产物，也是有氧呼吸等生物能途径的底物。虽然O2是相对惰性的，但它通过一个电子转移或能量转移反应转化为不同化学类别的有毒活性氧。当单个电子转移到O2时，它被还原为超氧化物，过氧化氢或羟基自由基。当能量转移到O2时，形成单线态氧（[1]O2）。我们有相当多的关于细胞如何对超氧化物、过氧化氢和羟基自由基作出反应的信息。然而，关于细胞如何响应[1]O2的知识相对较少，O2是一种常见的活性氧，可以破坏生物能量膜的完整性，破坏许多生物分子，产生突变或杀死细胞。为了纠正这种情况，我们将研究细菌对[1]O2的反应。我们的实验利用了已知的关于在α-变形杆菌类球红杆菌中产生[1]O2的条件的形成和响应。这是研究这种反应的生物系统的选择，因为光合生物，如R。类球形菌作为太阳能捕获的副产品产生大量的[1]O2。此外，我们已经确定了转录反应的条件下，产生[1]O2在这种细菌。这种对[1]O2的转录反应依赖于细胞质外功能家族中的另一种sigma因子sigmaE和反sigma因子ChrR。我们还获得了一个三维视图的sigmaE-ChrR复合物，控制转录响应[1]O2。在这个项目中，我们将确定[1]O2的存在如何增加sigmaE活性。[1]O2对缺乏sigmaE的细胞具有杀菌作用，因此我们也将鉴定保护细胞免受这种有毒活性氧的基因产物。[1]O2的化学性质预测，这种活性氧产生的损伤和在这种应激反应中起作用的活动将不同于超氧化物、过氧化氢或羟基自由基存在下产生的损伤和活动。微生物基因组序列分析表明，R. sphaeroides sigmaE和ChrR存在于许多光合细菌和非光合细菌中，这些细菌可能会遇到[1]其他途径产生的O2，作为植物和动物防御病原微生物的一部分。因此，我们的研究将回答有关许多细胞感知和保护自己免受[1]O2影响的能力以及[1]O2对蛋白质和其他生物分子的修饰性质的重要问题。真核细胞使用[1]O2来防御病原微生物，并在光动力疗法中杀死癌细胞，这预示着我们的发现将具有巨大的抗菌和治疗潜力。

DESCRIPTION (provided by applicant): Molecular oxygen (O2) is critical to life on this planet; it is a product of oxygenic photosynthesis and it is a substrate for bioenergetic pathways like aerobic respiration. While O2 is relatively inert, it is converted to different chemical classes of toxic reactive oxygen species by either one electron transfer or energy transfer reactions. When single electrons are transferred to O2, it is reduced to superoxide, hydrogen peroxide, or hydroxyl radicals. When energy is transferred to O2, singlet oxygen ([1]O2) is formed. We have considerable information about how cells respond to superoxide, hydrogen peroxide and hydroxyl radicals. However, relatively little is known about how cells respond to [1]O2, a common reactive oxygen species that can destroy the integrity of bioenergetic membranes, damage many biomolecules, generate mutations, or kill cells. To rectify this situation, we will study the bacterial response to [1]O2. Our experiments capitalize on what is known about the formation and response to conditions that generate [1]O2 in the alpha-proteobacterium Rhodobacter sphaeroides. This is the biological system of choice for studying this response since photosynthetic organisms like R. sphaeroides generate significant amounts of [1]O2 as a byproduct of solar energy capture. In addition, we have identified a transcriptional response to conditions that generate [1]O2 in this bacterium. This transcriptional response to [1]O2 depends on an alternative sigma factor in the extracytoplasmic function family, sigmaE, and the anti-sigma factor, ChrR. We have also obtained a 3-dimensional view of the sigmaE-ChrR complex that controls the transcriptional response to [1]O2. In this project, we will determine how the presence of [1]O2 increases sigmaE activity. [1]O2 is bacteriocidal to cells lacking sigmaE, so we will also identify gene products that protect cells from this toxic reactive oxygen species. The chemical properties of [1]O2 predict that the damage generated by this reactive oxygen species and the activities that function in this stress response will differ from those produced in the presence of superoxide, hydrogen peroxide or hydroxyl radicals. Analysis of microbial genome sequences indicates that homologs of R. sphaeroides sigmaE and ChrR are present in many photosynthetic bacteria plus non-photosynthetic bacteria that are likely to encounter [1]O2 generated by other pathways as part of plant and animal defenses against pathogenic microbes. Thus, our research will answer important questions about the ability of many cells to sense and protect themselves from [1]O2 and the nature of the modifications caused by [1]O2 to proteins and other biomolecules. The use of [1]O2 by eukaryotic cells to defend against pathogenic microbes and in photodynamic therapy to kill cancer cells predicts that our findings will have large antimicrobial and therapeutic potential.