Expression of clp genes in Streptococcus mutans

描述(申请人提供)：变形链球菌被认为是导致龋齿的主要病原体。变形链球菌也是感染性心内膜炎的重要病原体。这种微生物通过在牙齿表面形成不同的、多物种的生物膜来定植口腔，称为牙菌斑。这种病原体已经发展出多种机制来适应并在口腔恶劣的环境中茁壮成长。变形链球菌能够快速有效地对各种环境通量做出反应，包括严重的营养限制、pH和温度的波动以及氧化和渗透张力的变化。细菌暴露在这些不利的环境中，可以通过表达各种基因来诱导对各种环境挑战的交叉保护，从而诱导出一种应激耐受反应。逆境耐受基因受一组独特的转录调控因子的调控，包括交替的西格玛因子。然而，与其他病原体不同，变形链球菌和其他链球菌不编码任何替代的西格玛因子。另一方面，变形链球菌基因组中存在一些在其他细菌的应激反应中可能起作用的基因，但它们在胁迫和毒力中的作用尚未在变形链球菌中进行详细的研究。CLP(酪蛋白水解酶)家族就是这样一类蛋白质，参与热和氧化应激反应。CLP家族由一种称为ClpP的小细胞质丝氨酸蛋白酶和各种ATPase组成。变形链球菌编码5个CLP ATPase，ClpP与配对的CLP ATPase结合形成一个功能复合体，专门针对受损或错误折叠的蛋白质进行降解或易位。ATPase组分决定底物的特异性，而ClpP则降解受损的蛋白质。在大多数病原菌中，ClpP在毒力中起着非常重要的作用。例如，在变形链球菌中，ClpP是形成最佳生物膜和耐酸反应所必需的。虽然ClpP在该病的发病机制中起着重要作用，但对CLP基因在该病中的调控知之甚少。CLP基因的调控是非常复杂的，并且可以根据生物体的不同而显著不同。这项建议的主要目的是深入了解变形链球菌在正常和应激条件下生长过程中ClpP基因的表达。此外，我们还建议研究一种重要而独特的转录抑制因子CtsR，它对包括ClpP在内的CLP基因在适应性反应中的表达具有重要意义。我们预计，该项目的完成将导致在变形链球菌中发现新的应激反应基因表达调控途径。此外，从这个项目中获得的知识还可以扩展到对其他重要的革兰氏阳性病原体的分析，如肺炎链球菌和化脓性链球菌，并可能导致识别新的药物靶标。

DESCRIPTION (provided by applicant): Streptococcus mutans is considered as the major etiological agent in dental caries. S. mutans is also an important agent of infective endocarditis. The organism colonizes the oral cavity by forming diverse, multispecies biofilms on the tooth surface, known as dental plaque. This pathogen has developed multiple mechanisms to adapt and to flourish in the hostile environment of the oral cavity. S. mutans has the ability to respond rapidly and efficiently to various environmental fluxes, including severe nutrient limitation, fluctuations in pH and temperature, and changes in oxidative and osmotic tensions. Exposure of bacteria to these adverse environments can induce a stress tolerance response through expression of a wide variety of genes that provides cross-protection against diverse environmental challenges. Stress tolerance genes are regulated by unique groups of transcriptional regulators, including alternate sigma factors. However, unlike other pathogens, S. mutans and other streptococci do not encode any alternate sigma factors. On the other hand, some genes that putatively function in stress responses in other bacteria are present in the S. mutans genome, but their role in stress and virulence has not been investigated in S. mutans in great detail. One such group is the Clp (caseinolytic protease) family of proteins that are involved in thermal and oxidative stress responses. The Clp family is composed of a small cytoplasmic serine protease, called ClpP, and various ATPases. S. mutans encodes five Clp ATPases and ClpP associates with a partner Clp ATPase to form a functional complex that specifically targets damaged or misfolded proteins for degradation or translocation. While the ATPase component determines the substrate specificity, ClpP degrades the damaged protein. In most pathogens, ClpP plays a very important role in virulence. For example, in S. mutans, ClpP is required for optimal biofilm formation and acid-tolerance response. Although ClpP play important roles for the pathogenesis, very little is known about the regulation of the clp genes in this pathogen. Regulation of the clp genes is very complex, and can vary significantly depending on the organism. The main goal of this proposal is to gain insight into the expression of the clpP gene during S. mutans growth under normal and stressful conditions. Furthermore, we also propose to study an important and unique transcriptional repressor, CtsR, which is important for clp genes, including clpP, expression during adaptive response. We anticipate that completion of this project will lead to the identification of novel regulatory pathway for expression of stress response genes in S. mutans. Moreover, knowledge acquired from this project can also be extended to analysis of other important gram-positive pathogens such as S. pnemoniae and S. pyogenes, and may lead to the identification of novel drug targets.