Characterization of a unique two-component system in streptococci

描述（由申请人提供）：细菌有许多双组分信号转导系统（TCSs），通过改变反应调节因子的磷酸化状态来响应特定的环境信号。尽管这些系统被认为形成了一个复杂的信号网络，但它们如何相互作用的详细机制在很大程度上仍未得到解释。在本应用中，我们将以变形链球菌为模式生物，研究细菌中一种新的信号通路。变形链球菌被认为是龋齿的主要病因，有时也会引起感染性心内膜炎。这种病原体通过形成多物种生物膜在口腔中定植，并发展出多种机制来适应和在口腔的敌对环境中繁殖。我们发现一种特殊的TCS， LiaFSR，除了传感器激酶（LiaS）和反应调节因子（LiaR）外，还编码一种额外的蛋白（LiaF），调节gbpC的表达，gbpC编码一种葡聚糖结合蛋白，这是生物膜形成和心内膜炎发生所必需的。我们还发现，LiaFSR是产生诱变素（一种细菌素）的必要条件，可以抑制生物膜群落中其他竞争细菌的生长。最近的一项微阵列研究显示，174个基因，约占基因组的9%，受这种TCS调节。在芽孢杆菌和葡萄球菌中，这种TCS参与感知由各种抗生素引起的细胞壁损伤，特别是那些干扰脂质- II周期的抗生素。然而，该TCS所感知的信号及其在链球菌中信号转导的分子机制尚不清楚。一个令人困惑的问题是，在变形链球菌中，LiaS和说谎者是如何调节靶基因表达的，因为说谎者的失活在许多情况下不会产生任何明显的表型。在本应用中，基于我们的初步结果，我们提出了一个模型来解释LiaS和LiaR如何参与信号转导。我们还提出了LiaF在LiaSR介导的基因调控中的可能作用。具体目标1和2旨在验证我们的假设，以确定LiaS和LiaF参与信号转导的机制。目的3是了解说谎者结合DNA的分子机制。在完成后，我们希望确定LiaFSR的细胞作用，这可能会导致更大的方法来控制这种病原体。这项研究也将促进我们对变形链球菌和其他相关病原体（如A-和B-链球菌）基因调控和信号转导的分子机制的全面认识。

DESCRIPTION (provided by applicant): Bacteria have many two-component signal-transduction systems (TCSs) that respond to specific environmental signals by altering the phosphorylated state of a response regulator. Although these systems are presumed to form an intricate signal network, the detailed mechanism of how they interact with each other remains largely unexplained. In this application, we will use Streptococcus mutans as a model organism to study a novel signaling pathway in bacteria. S. mutans is considered to be the primary etiological agent of dental caries and sometimes in infective endocarditis. This pathogen colonizes the oral cavity by formation of multispecies biofilm and has developed a variety of mechanisms to adapt and to flourish in the hostile environment of the oral cavity. We found that one particular TCS, LiaFSR, which encodes an extra protein (LiaF) in addition to the sensor kinase (LiaS) and the response regulator (LiaR), regulates the expression of gbpC that encodes a glucan-binding-protein necessary for biofilm formation and the onset of endocarditis. We also found that LiaFSR is necessary for the production of mutacin, a bacteriocin, to suppress the growth of other competitor bacteria present in the biofilm community. A recent microarray study revealed that 174 genes, ~9% of the genome, are regulated by this TCS. In Bacillus and Staphylococcus, this TCS is involved in sensing cell wall damage caused by various antibiotics, particularly those antibiotics that interfere with the lipid- II cycle. However, the signals sensedby this TCS and the molecular mechanism of signal transduction in streptococci are yet to be identified. A puzzling question is how LiaS and LiaR regulate target gene expression in S. mutans, since inactivation of LiaR does not produce, in many cases, any noticeable phenotypes. In this application, based on our preliminary results, we propose a model to explain how LiaS and LiaR may participate in signal transduction. We also propose a possible role for LiaF in LiaSR mediated gene regulation. Specific Aims 1 and 2 are designed to test our hypothesis to determine the mechanisms by which LiaS and LiaF participate in signal transduction. The goal of Aim 3 is to understand the molecular mechanism of DNA binding by LiaR. Upon completion, we hope to determine the cellular role of the LiaFSR that may lead to greater means of controlling this pathogen. This investigation will also promote our overall understanding of the molecular mechanisms of gene regulation and signal transduction in S. mutans and other related pathogens such as group A- and group B- streptococcus. PUBLIC HEALTH RELEVANCE: Bacteria have many two-component signal-transduction systems (TCSs) that respond to specific environmental signals by altering the phosphorylated state of a response regulator. Although these systems are presumed to form an intricate signal network, the detailed mechanism of how they interact with each other remains largely unexplained. In this application we propose to unravel a novel interaction between a TCS and another signaling pathway in Streptococcus mutans, a bacterium that resides in the human oral cavity and forms bacterial communities on the tooth surface known as dental plaque. S. mutans causes tooth decay, an extremely costly global health problem that affects 60-90% of school children and many adults in industrialized countries, and results in annual expenditures of billions of dollars in the U.S. alone. Our study focuses on the regulation of genes that encode products that enable this pathogen to survive in the oral cavity and to cause tooth decay. Successful completion of our studies could lead to the development of novel therapeutic treatments to limit the growth of this bacterium and reduce tooth decay.