Immune Modulation by Bacterial Autolysins

描述（由申请人提供）：SecA2辅助蛋白分泌系统用于从许多革兰氏阳性病原体中分泌促毒蛋白，包括炭疽芽孢杆菌（a类）和单核增生李斯特菌（B类）。我们鉴定了两种依赖seca2的自溶蛋白，它们在感染动物体内促进单核增生乳杆菌的毒力，但不影响该细菌在组织培养细胞中的生长。缺乏p60的工程细菌突变体的毒力可以通过表达全长p60来恢复，但不能通过表达截断的催化活性蛋白来恢复。p60的催化特异性预示着它可以消化肽聚糖（PGN）来产生或破坏免疫调节的PGN片段（多肽），分别包括二肽和三肽（MDP和MTP）。MDP和MTP通过作用于Nod家族的细胞质蛋白来影响哺乳动物细胞的细胞因子反应。我们发现表达p60的细菌和这些细菌释放的小分子增强了巨噬细胞对特异性免疫调节细胞因子的诱导。在这项拨款提案中，我们研究p60如何促进毒力和影响宿主对感染的先天免疫反应。我们的第一个目标是确定p60的特征，这些特征是PGN消化所必需的，以及它对细菌毒力和细胞因子基因表达的影响。我们的第二个目标是研究p60依赖性生物活性多肽或小分子的结构和系统发育分布，并测试对该分子的反应是否需要已知的多肽反应Nod家族蛋白。对于我们的第三个目标，我们通过确定p60和由p60诱导的细胞因子的表达如何影响巨噬细胞对激活刺激的反应来研究p60对细菌毒力影响的潜在机制。我们的研究将确定这种细菌自溶素对临床重要细菌病原体的毒力的作用机制，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病原体。

DESCRIPTION (provided by applicant): 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.