Integration of metabolism and virulence in Gram-positive bacteria

描述（由申请人提供）：细胞内代谢是所有生物中交叉反应的复杂网络。在革兰氏阳性细菌中，CodY蛋白是主要的 BCAA是多种代谢途径和调控方案的整合者，帮助细胞响应四种代谢物（三种支链氨基酸（BCAA;异亮氨酸、亮氨酸和缬氨酸）和GTP）的细胞内库开启或关闭许多途径。在致病性革兰氏阳性菌中，CodY也是毒力基因的主要调节因子。取决于生物体和特定毒力基因产物的作用，CodY可以作为负或正调节剂，并且可以抑制或刺激发病机制。CodY的这一特性通过将细菌对宿主造成损害的决定与几种关键代谢物的库联系起来，以一种重要的方式将发病机制与细胞的生理状态联系起来。然而，并非所有的CodY靶基因对CodY介导的调控都同样敏感。也就是说，由于营养物质可利用性的变化，BCAA和GTP的细胞内库的变化产生了CodY分子总群体的不同部分活跃的情况。因此，一些基因（例如，对CodY具有非常高亲和力的靶基因）在其它基因（例如，具有低亲和力靶的那些）几乎根本不被抑制。因此，CodY调控的基因属于调控谱或层次。该项目的主要目标是确定模式生物枯草芽孢杆菌福尔斯中每个CodY调节基因落在该谱内的位置，将基因的定位与CodY效应分子的细胞内库偶联，确定负责建立基因调节谱的分子机制，并确定在不同的养分供应水平下被诱导或抑制的代谢途径。这项分析有望为细胞如何优先使用特定代谢途径以应对一般营养限制提供新的见解。类似的研究与两个重要的人类病原体，金黄色葡萄球菌和艰难梭菌，将揭示在CodY层次结构中的各种毒力基因的下落。CodY是两个物种中毒力的主要阻遏物。这些结果将对导致细菌从寄生性生活方式转变为致病性生活方式的特定代谢限制的程度提供前所未有的看法。此外，对于复杂的病原体，如S.金黄色葡萄球菌，表达几十种毒力因子，对宿主造成不同程度的损害，将有可能了解在最具破坏性的因子被诱导之前，代谢物库必须下降到什么程度。 公共卫生相关性：细菌具有适应许多不同环境条件和压力的非凡能力。这种能力极大地影响了它们对栖息地的选择以及它们引起人类疾病的条件。这一建议旨在揭示细菌将致病基因的表达与特定细胞内化合物的积累相结合的主要机制。了解哪些化合物会影响发病机制有望导致新型抗感染药物的开发。

DESCRIPTION (provided by applicant): Intracellular metabolism is a complex network of intersecting reactions in all living things. In Gram-positive bacteria, the CodY protein is a major integrator of diverse metabolic pathways and regulatory schemes, helping the cell to turn many pathways on or off in response to the intracellular pools of four metabolites, the three branched-chain amino acids (BCAAs; isoleucine, leucine and valine) and GTP. In pathogenic Gram-positive bacteria, CodY is also a major regulator of virulence genes. Depending on the organism and the role of a specific virulence gene product, CodY, may act as either a negative or a positive regulator and may either inhibit or stimulate pathogenesis. This property of CodY links pathogenesis in an important way to the physiological state of the cell by tying the bacterium's decision to cause damage to the host to the pools of just a few key metabolites. Not all CodY target genes, however, are equally sensitive to CodY-mediated regulation. That is, variations in the intracellular pools of the BCAAs and GTP due to variations in nutrient availability create situations in which different fractions of the total population of CodY molecules are active. As a result, some genes (e.g., those that have very high affinity targets for CodY) are fully repressed under conditions in which other genes (e.g., those with low affinity targets) are hardly repressed at all. Thus, CodY-regulated genes fall within a regulatory spectrum or hierarchy. A major goal of the proposed project is to determine where each CodY-regulated gene in the model organism, Bacillus subtilis, falls within this spectrum, to couple the positioning of genes to the intracellular pools of the CodY effector molecules, to determine the molecular mechanisms that are responsible for establishing the spectrum of gene regulation, and to identify the metabolic pathways that are induced or repressed at different levels of nutrient availability. This analysis s expected to provide novel insight into how the cell prioritizes the usage of specific metabolic pathways in response to general nutrient limitation. Analogous studies with two important human pathogens, Staphylococcus aureus and Clostridium difficile, will reveal where within the CodY hierarchy various virulence genes fall. CodY is a major repressor of virulence in both species. The results will give an unprecedented view of the extent of specific metabolic limitation that causes a bacterium to turn from a commensal life style to a pathogenic life style. Moreover, for a complex pathogen, such as S. aureus, that expresses dozens of virulence factors that cause different extents of damage to the host, it will be possible to learn to what extent metabolite pools have to drop before the most damaging factors are induced. PUBLIC HEALTH RELEVANCE: Bacteria have a remarkable ability to adapt to many different environmental conditions and stresses. This ability greatly influences both their choice of habitats and the conditions under which they cause human disease. This proposal seeks to reveal a principal mechanism by which bacteria couple the expression of pathogenesis genes to the accumulation of specific intracellular compounds. Knowing which compounds affect pathogenesis is expected to lead to the development of novel anti-infectives.