Expression of clp genes in Streptococcus mutans

描述（申请人提供）：变形链球菌被认为是龋齿的主要病因。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多种多样的生物膜，即牙菌斑，在口腔中定居。这种病原体已经发展出多种机制来适应并在口腔的敌对环境中蓬勃发展。变形链球菌能够快速有效地应对各种环境变化，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多种基因来诱导应激耐受性反应，这些基因提供了针对不同环境挑战的交叉保护。应激耐受性基因是由独特的转录调控因子群调控的，包括备用sigma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备用sigma因子。另一方面，一些被认为在其他细菌的应激反应中起作用的基因存在于变形链球菌的基因组中，但它们在应激和毒力中的作用尚未在变形链球菌中得到详细的研究。其中一组是Clp（酪蛋白溶解蛋白酶）家族蛋白，它参与热应激和氧化应激反应。Clp家族由一个小的细胞质丝氨酸蛋白酶ClpP和各种atp酶组成。S. mutans编码5种Clp atp酶，ClpP与一个Clp atp酶伙伴结合形成一个功能复合物，专门针对受损或错误折叠的蛋白质进行降解或易位。而atp酶成分决定底物特异性，ClpP降解受损蛋白。在大多数病原体中，ClpP在毒力中起着非常重要的作用。例如，在变形链球菌中，ClpP是最佳生物膜形成和耐酸反应所必需的。尽管ClpP在发病机制中发挥重要作用，但对clp基因在该病原体中的调控作用知之甚少。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变化。本研究的主要目的是深入了解突变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，我们还建议研究一个重要且独特的转录抑制因子CtsR，它在适应性反应中对clp基因（包括clpP）的表达很重要。我们预计，该项目的完成将导致突变链球菌应激反应基因表达的新调控途径的鉴定。此外，从该项目中获得的知识也可以扩展到分析其他重要的革兰氏阳性病原体，如肺炎链球菌和化脓性链球菌，并可能导致新的药物靶点的鉴定。

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.