Immune Modulation by Bacterial Autolysins

SecA 2辅助蛋白分泌系统是从大肠杆菌中分泌毒力促进蛋白所必需的。 一些革兰氏阳性病原体，包括炭疽杆菌（A类）和单核细胞增生李斯特菌 （B类）。我们鉴定了两个依赖SecA 2的自溶蛋白，它们促进了L. 在受感染的动物中的单核细胞增多症，但不影响这种细菌在组织培养细胞中的生长。的 缺失p60的工程化细菌突变体的毒力通过全长p60的表达而恢复，但不 通过表达截短的无催化活性的蛋白质。p60的催化特异性预示着它 刺激肽聚糖（PGN）以产生或破坏免疫调节PGN片段（胞肽）， 分别包括胞壁酰二肽和三肽（MDP和MTP）。MDP和MTP影响哺乳动物 通过作用于Nod家族的胞质蛋白质来调节细胞因子应答。我们发现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 免疫调节细胞因子。在这项拨款申请中，我们研究了p60如何促进 毒力和影响宿主对感染的先天免疫反应。我们的第一个目标将确定p60的特征 PGN消化及其对细菌毒力和细胞因子基因表达的影响所需的。 我们的第二个目的是研究p60依赖的生物学上的结构和系统发育分布。 并测试对该分子的应答是否需要已知的 Nod家族蛋白。对于我们的第三个目标，我们研究了一个潜在的机制， p60对细菌毒力的影响，通过确定p60的表达及其诱导的细胞因子 影响巨噬细胞对激活刺激的反应。我们的研究将确定这一机制， 细菌自溶素有助于临床上重要的细菌病原体的毒力，并且开始 探索类似的机制是否促进其他革兰氏阳性病原体的毒力，包括潜在的 生物恐怖分子。 致病菌致病的机制包括破坏宿主免疫系统的策略， 应答一种颠覆性的战略，可能是共同的一些致命的细菌是研究在这一点上， 格兰特.我们的研究将确定这种免疫颠覆策略的分子基础， 揭示了在细菌感染、疫苗接种和免疫过程中调节炎症的新的治疗途径， 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.