Low pH-mediated membrane biosynthesis in S. mutans.

描述（由申请人提供）：口腔传染病仍然是现代牙科的主要挑战。龋齿和牙周病被认为是工业化国家最普遍的疾病。主要的口腔传染病是由机会性病原体引起的，Philip Marsh回顾了（微生物学149:279-294,2003）将口腔传染病视为生态灾难的主要例子的基础。疾病的发生是口腔生物膜群落由于应激条件而发生变化的结果；因此，偏爱具有所谓致病特性的生物体。例如，高酸性生物或那些具有高能力诱导宿主炎症反应的生物可能在这些条件下茁壮成长。开发除抗生素以外的新型抗菌剂，可能是目前预防和治疗口腔传染病最有前途的方法。我们已经证明，单不饱和膜脂肪酸（UFAs）的形成对于变形链球菌在酸性环境中生存的能力很重要（Fozo和Quivey， 2004a和b）。此外，我们已经证明变形链球菌中不饱和脂肪酸的形成依赖于一种酶，FabM （Fozo和Quivey， 2004b）。我们在“初步研究”一节中加入了更多的最新数据，表明FabM的缺失显著降低了变形链球菌在大鼠中引起疾病的能力。目前仅在3种细菌属中发现了FabM酶：链球菌。葡萄球菌和梭杆菌。因此，对这种酶在变形链球菌中的作用的了解将有助于了解其他重要的人类病原体。然而，我们目前缺乏关于膜生物合成酶的调控，以及变形链球菌如何利用这些酶来控制膜稳态的信息。我们的假设是变形链球菌调节其膜组成以响应外部酸化，以维持膜流动性的稳态。我们提出了一系列的实验来完成我们早期的工作并检验我们的假设。[我们的目标是全面了解变形链球菌在低ph生长过程中的膜生物合成。我们的具体目标如下：1)我们将完成膜ph依赖性变化的生化表征，目标是测量磷脂和支链脂肪酸的变化；2)我们将利用生化和分子工具确定fab基因的遗传调控机制以及fabR在fab基因簇调控中的作用；3)我们将利用生物化学和遗传学工具来阐明FabM和FabK与膜组成的关系；4)我们将确定变形链球菌膜中ph依赖性变化与流动性的关系；5)最后，我们将确定变形链球菌如何利用其fab基因对膜破坏剂（如蓝蛋白和tt-法尼醇）做出反应。

DESCRIPTION (provided by applicant): Oral infectious diseases remain major challenges in modern Dentistry. Caries and periodontal diseases are considered to be the most prevalent diseases in the industrialized world. The major oral infectious diseases are caused by opportunistic pathogens, and Philip Marsh has reviewed (Microbiology 149:279-294, 2003) the basis for considering Dental infectious diseases as prime examples of ecological catastrophes. Disease occurs as a result of shifts, due to stress conditions, in oral biofilm communities; thereby, favoring organisms that possess so-called pathogenic personalities. For example, highly aciduric organisms or those with high capacities to induce inflammatory responses of the host might thrive under these conditions. The development of new types of antimicrobials, other than antibiotics, is currently perhaps the most promising approach for preventing and treating oral infectious diseases. We have shown that the formation of mono- unsaturated membrane fatty acids (UFAs) is important for the ability of S. mutans to survive acidic environments (Fozo and Quivey, 2004a and b). Further, we have shown that the formation of unsaturated fatty acids in S. mutans is dependent on a single enzyme, FabM (Fozo and Quivey, 2004b). We include more recent data in the Preliminary Studies section to show that loss of FabM dramatically lowers the ability of S. mutans to cause disease in rats. The FabM enzyme is presently identified in only 3 bacterial genera: the Streptococci. Staphylococci, and Fusobacteria. Thus, knowledge about the role of the enzyme in S. mutans will shed light on other important human pathogens. Nevertheless, we are currently lacking information regarding the regulation of membrane biosynthesis enzymes, and how those enzymes are used by S. mutans to control membrane homeostasis. Our hypothesis is that S. mutans regulates its membrane composition in response to external acidification in order to maintain homeostasis in membrane fluidity. We propose a series of experiments designed to complete our earlier work and to test our hypothesis. [Our goal is to achieve a thorough understanding of the S. mutans membrane biosynthesis during growth at low pH. Our Specific Aims are as follows: 1) we will complete our biochemical characterization of pH-dependent changes in membranes, with the goal of measuring changes in phospholipids and branched chain fatty acids; 2) we will use biochemical and molecular tools to determine the mechanism of genetic regulation of fab genes and the role of fabR in regulating the fab gene cluster; 3) we will use biochemical and genetic tools to elucidate the relationship of FabM and FabK to membrane composition; 4) we will determine how pH-dependent changes in S. mutans membranes relate to fluidity; 5) finally, we will determine how S. mutans uses its fab genes to respond to membrane disrupting agents such as cerulenin and tt-farnesol.