Streptococcus gordonii Rgg regulators: gene expression, signaling, oral biofilms

描述(申请人提供)：戈登链球菌是牙菌斑生物膜的先驱定植者。它们在表面的积累是由单一的胞外葡萄糖基转移酶(GTF)酶从饮食中的蔗糖合成的葡聚糖促进的。戈登葡萄球菌GTF结构基因gtfG的调控由上游基因rgg控制，rgg编码一种转录激活因子，是RGG调节蛋白家族中第一个被发现的成员。戈登链霉菌染色体上编码有7个RgG家族蛋白，其中包括部分鉴定的RggD，它可能参与葡聚糖非依赖性生物膜的形成。基因组序列数据表明，RGG家族基因在革兰氏阳性细菌中广泛存在；有关RGG家族共同和独特特征的数据正在涌现。RGG蛋白通常控制相邻基因的转录，这些基因参与多种生物学功能，包括定殖、毒力和对环境条件的反应。RGG家族蛋白可以增加或减少其目标基因的表达，通常是以一种生长阶段依赖的方式。一些RGG不仅控制相邻基因的表达，而且像在化脓性链球菌中一样，充当位于整个染色体上的多个基因的启动子的全局调节器。我们的数据有力地表明，除了gtfG外，戈登链球菌RGG可能还发挥着类似的全球调控作用，影响基因的表达。最近在非口腔链球菌物种中的一个令人兴奋的发现是，一些RGG蛋白的调节是由多肽信号介导的，这些信号以信息素的方式发挥作用，并作为群体感应分子来协调细菌群落的反应。这些信息素是由位于RGG基因附近的开放阅读框编码的前肽加工而成的；这些肽可以对同源RGG的活性产生积极或消极的影响。这种新发现的基因调控机制为探索口腔生物膜控制的新机制提供了有趣的可能性。基于信息素与RGG蛋白相互作用的新证据，我们假设RGG家族调节因子可能具有共同的作用机制，并且尚不确定的多肽可能影响戈登链球菌RGG蛋白的活性。拟议的研究将探讨这种可能性，并通过以下具体目标提供对戈登链霉菌RGG家族蛋白功能的更多见解：1)通过比较亲本和突变株中基因的表达和由此产生的表型，鉴定和初步鉴定受RGG家族决定因素控制的选定的戈尔顿链霉菌靶基因；2)通过检测培养滤液和合成肽存在下的RGG活性，确定戈尔顿链霉菌RGG蛋白的活性是否受到潜在的信息素样肽的影响。数据将用作未来R01应用程序的基础。希望这些研究将确定口腔生物膜形成的新方面，也可能为其他革兰氏阳性细菌中RGG家族蛋白的基因调控提供普遍适用的见解。

DESCRIPTION (provided by applicant): Streptococcus gordonii are pioneer colonizers of dental plaque biofilms. Their accumulation on surfaces is facilitated by glucans synthesized from dietary sucrose by the single extracellular glucosyltransferase (Gtf) enzyme. Regulation of the S. gordonii Gtf structural gene, gtfG, is controlled by the upstream gene, rgg which encodes a transcriptional activator that was the first-identified member of the Rgg family of regulatory proteins. There are seven Rgg-family proteins encoded in the S. gordonii chromosome including the partially characterized RggD which may be involved in glucan-independent biofilm formation. Genome sequence data have shown the widespread occurrence of rgg-family genes among Gram-positive bacteria; data are emerging about shared and unique features of the Rgg family. Rgg proteins usually control transcription of adjacent genes which are involved in various biological functions including colonization, virulence and responses to environmental conditions. Rgg-family proteins can increase or decrease expression of their target genes, often in a growth phase-dependent fashion. Some Rggs control not only the expression of adjacent genes, but act as global regulators acting at promoters of multiple genes located throughout the chromosome as occurs in Streptococcus pyogenes. Our data strongly suggest that S. gordonii Rgg may play similar global regulatory roles affecting expression of genes in addition to gtfG. An exciting recent finding in non-oral streptococcal species is that regulation by some Rgg proteins is mediated by peptide signals that function in a pheromone-like manner and act as quorum sensing molecules to coordinate the bacterial community response. These pheromones are processed from pre-peptides that are often encoded by open reading frames located near rgg genes; these peptides can positively or negatively affect the activity of the cognate Rgg. This newly-discovered mechanism of gene regulation holds intriguing possibilities for exploring novel mechanisms of oral biofilm control. Based upon the emerging evidence for pheromone interactions with Rgg proteins, we hypothesize that Rgg-family regulators may share common mechanisms of action and that as-yet-unidentified peptides may influence the activity of the S. gordonii Rgg proteins. The proposed studies will examine this possibility and provide additional insights into the function of S. gordonii Rgg family proteins via the following Specific Aims: 1) t identify and perform a preliminary characterization of selected S. gordonii target genes controlled by rgg-family determinants by comparing gene expression and resulting phenotypes in parental and mutant strains; 2) to determine if activities of S. gordonii Rgg proteins are influenced by potential pheromone-like peptides by examination of Rgg activity in the presence of both culture filtrates and synthetic peptides. Data will be used as a foundation for a future R01 application. It is hoped that these studies will identify novel facets of oral biofilm formatio that may also provide generally- applicable insights into genetic regulation by Rgg-family proteins in other Gram-positive bacteria.