Immune Modulation by Bacterial Autolysins

SecA2辅助蛋白分泌系统是细菌产生毒力促进蛋白所必需的。 革兰氏阳性病原体的数量，包括炭疽芽孢杆菌(A类)和单核细胞增多性李斯特菌 (B类)。我们鉴定了两个依赖于SecA2的自溶蛋白，它们促进了L. 感染动物的单核细胞增多症，但不影响这种细菌在组织培养细胞中的生长。这个 缺乏p60的工程菌突变株的毒力可以通过表达全长p60来恢复，但不能 通过表达一种截短的、催化失活的蛋白质。P60的催化专一性预示着它 消化肽聚糖(PGN)以产生或破坏免疫调节PGN片段(肌肽)， 分别包括胞壁酰二肽和三肽(MDP和MTP)。MDP和MTP对哺乳动物的影响 作用于NOD家族胞浆蛋白的细胞细胞因子反应。我们发现了p60- 表达细菌和从这些细菌释放的小分子增强了特异性的诱导 巨噬细胞的免疫调节细胞因子。在这项拨款提案中，我们调查了p60是如何促进 毒力和影响宿主对感染的先天免疫反应。我们的首要目标是确定p60的特征。 这对于PGN的消化及其对细菌毒力和细胞因子基因表达的影响是必要的。 我们的第二个目标是研究依赖p60的生物学基因的结构和系统发育分布。 活性多肽或小分子，并测试对该分子的反应是否需要已知 多肽反应性NOD家族蛋白。为了我们的第三个目标，我们研究了一种潜在的机制 P60‘S通过检测p60蛋白和细胞因子的表达对细菌毒力的影响 影响巨噬细胞对激活刺激的反应。我们的研究将确定这一点的机制 细菌自溶素有助于一种临床重要细菌病原体的毒力，并开始 探索类似的机制是否会促进其他革兰氏阳性病原体的毒力，包括潜在的 生物恐怖主义的代理人。 病原菌致病的机制包括破坏宿主免疫的策略。 回应。在这篇文章中，研究了一种可能对许多致命细菌通用的颠覆性策略。 格兰特。我们的研究将确定这种免疫颠覆策略的分子基础，并可能因此 揭示新的治疗途径，以调节细菌感染、疫苗接种和 慢性炎症性疾病。

The SecA2 auxiliary protein secretion system is required for secretion of virulence promoting proteins from a number of Gram-positive pathogens, including Bacillus anthracis (category A) and Listeria monocytogenes (category B). We identified two SecA2-dependent autolytic proteins that promote virulence of L. monocytogenes in infected animals, yet do not affect the growth of this bacterium in tissue culture cells. The virulence of engineered bacterial mutants lacking p60 was restored by expression of full-length p60, but not by expression of a truncated, catalytically inactive protein. The catalytic specificity of p60 predicts that it digests peptidoglycan (PGN) to generate or destroy immune modulating PGN fragments (muropeptides), including respectively muramyl di- and tri-peptides (MDP and MTP). MDP and MTP influence mammalian cell cytokine responses by acting on cytosolic proteins of the Nod family. We have found that p60- expressing bacteria and small molecules released from these bacteria enhance the induction of specific immune-regulatory cytokines by macrophages. In this grant proposal we investigate how p60 promotes virulence and affects host innate immune responses to infection. Our first Aim will identify features of p60 that are required for PGN digestion and for its effects on bacterial virulence and cytokine gene expression. Our second Aim investigates the structure and phylogenetic distribution of a p60-dependent biologically active muropeptide or small molecule and tests whether responses to this molecule require known muropeptide-responsive Nod family proteins. For our third Aim, we investigate a potential mechanism for p60's effects on bacterial virulence by determining how expression of p60 and cytokines induced by p60 affect macrophage responses to activating stimuli. Our studies will define the mechanisms by which this bacterial autolysin contributes to the virulence of a clinically important bacterial pathogen and begin to explore whether similar mechanisms promote virulence of other Gram-positive pathogens, including potential agents of bioterrorism. The mechanisms used by pathogenic bacteria to cause disease include strategies to subvert host immune responses. A subversive strategy that may be common to a number of deadly bacteria is studied in this grant. Our studies will define the molecular basis for this strategy of immune subversion and may thus reveal novel therapeutic avenues to modulate inflammation during bacterial infection, vaccination, and chronic inflammatory diseases.