Bacterial Response to Singlet Oxygen

描述(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量途径的底物。虽然O2是相对惰性的，但它可以通过一个电子转移反应或能量转移反应转化为不同化学类别的有毒活性氧物种。当单电子被转移到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)。关于细胞对超氧化物、过氧化氢和羟基自由基的反应，我们有大量的信息。然而，人们对细胞对O2的反应知之甚少。O2是一种常见的活性氧物种，可以破坏生物能膜的完整性，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阿尔法蛋白细菌球形红细菌中产生[1]O2的条件的形成和反应。这是研究这一反应的生物系统的选择，因为光合作用的有机体，如球藻，会产生大量的氧气，作为太阳能捕获的副产品。此外，我们已经确定了对这种细菌产生[1]O2的条件的转录反应。这种对[1]O2的转录反应依赖于胞质外功能家族中的另一种sigma因子，sigmaE和抗sigma因子CHRR。我们还获得了控制对[1]O2转录反应的sigmaE-CHRR复合体的三维视图。在这个项目中，我们将确定[1]O2的存在如何增加SigmaE的活性。[1]O2对缺乏SigmaE的细胞具有杀菌作用，因此我们还将鉴定保护细胞免受这种有毒的活性氧物种伤害的基因产品。[1]O2的化学性质预测，这种活性氧物种产生的损害和在这种应激反应中起作用的活性将不同于在存在超氧化物、过氧化氢或羟基自由基的情况下产生的损害。因此，我们的研究将回答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造成的修饰的性质等重要问题。真核细胞使用[1]O2来防御病原体，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.