PPE Export by the Essential ESX-5 Secretion System in M. tuberculosis Virulence

项目总结/摘要 结核分枝杆菌（Mtb）需要ESX-5 VII型蛋白分泌系统进行体外生长。 由于ESX-5是必不可少的，因此ESX-5在结核分枝杆菌毒力和通过ESX-5输出的蛋白质中所起的作用 支持结核分枝杆菌复制的蛋白质的特征仍然很差。在相关病原体海洋分枝杆菌中， ESX-5输出分枝杆菌特有的PE和PPE蛋白家族的许多蛋白质。几 结核分枝杆菌PE和PPE蛋白定位于细胞壁，最近被认为与获得多种 营养素PE和PPE分泌的流行模型表明它们以异二聚体的形式输出， 唯一，并且该导出由EspG伴侣促进，该伴侣将PE-PPE对定向到同源ESX 用于出口的分泌系统。本提案将检验结核分枝杆菌需要ESX-5活性的中心假设， ESX-5底物的一个子集，其输出独立于EspG 5毒力伴侣。这 假设是基于使用Mtb菌株的初步数据，其中EccD 5，一种ESX-5分泌机制， 在一些实施方案中，EspG 5分子伴侣可以是亚基或EspG 5分子伴侣，或者EspG 5分子伴侣可以是条件性耗尽的。EccD 5而非EspG 5限制性Mtb的消耗 生长在巨噬细胞和某些碳源上。具体目标1将确定ESX-5的作用， Mtb毒力中的EspG 5伴侣，使用EccD 5或EspG 5以及巨噬细胞和 小鼠气溶胶感染模型。Specific Aim 2将使用ESX-5条件性耗竭菌株鉴定PPE 需要ESX-5活性但不需要EspG 5分子伴侣的蛋白质用于导出和连接ESX-5活性以使用 特定的营养素。具体目标3将检查PE蛋白之间的功能冗余，以促进 某些PPE蛋白的输出和使用小鼠气溶胶感染模型促进Mtb毒力。的 拟议的研究在概念上是创新的，因为它挑战了现有的ESX-5基板输出模型 通过暗示PE和PPE蛋白之间的混杂配对以及某些PPE蛋白的输出， 独立于EspG 5分子伴侣。这项拟议中的研究意义重大，因为预计它将表明， Mtb的发病机制需要ESX-5活性。这些知识将使ESX-5成为 开发新的抗结核药物，并支持将ESX-5分泌的抗原纳入新的 结核病疫苗。

PROJECT SUMMARY/ABSTRACT Mycobacterium tuberculosis (Mtb) requires the ESX-5 Type VII protein secretion system for in vitro growth. Because ESX-5 is essential, the role that ESX-5 plays in Mtb virulence and the proteins exported via ESX-5 that support Mtb replication remain poorly characterized. In the related pathogen Mycobacterium marinum, ESX-5 exports many proteins of the PE and PPE protein families that are unique to the mycobacteria. Several Mtb PE and PPE proteins localize to the cell wall and were recently implicated in acquisition of diverse nutrients. The prevailing model of PE and PPE secretion suggests they are exported as heterodimers that pair uniquely and that export is promoted by an EspG chaperone that targets the PE-PPE pair to the cognate ESX secretion system for export. This proposal will test the central hypothesis that Mtb requires ESX-5 activity and a subset of ESX-5 substrates that are exported independently of the EspG5 chaperone for virulence. This hypothesis is based on preliminary data using Mtb strains in which EccD5, an ESX-5 secretion machinery subunit, or the EspG5 chaperone can be conditionally depleted. Depletion of EccD5 but not EspG5 limited Mtb growth in macrophages and on certain carbon sources. Specific Aim 1 will determine the role of ESX-5 and the EspG5 chaperone in Mtb virulence using conditional depletion of EccD5 or EspG5 and both macrophage and mouse aerosol infection models. Specific Aim 2 will use the ESX-5 conditional depletion strains to identify PPE proteins that require ESX-5 activity but not the EspG5 chaperone for export and connect ESX-5 activity to use of specific nutrients. Specific Aim 3 will examine functional redundancy between PE proteins in facilitating export of certain PPE proteins and promoting Mtb virulence using the mouse aerosol infection model. The proposed research is conceptually innovative because it challenges existing models of ESX-5 substrate export by suggesting promiscuous pairing between PE and PPE proteins and export of certain PPE proteins independent of the EspG5 chaperone. The proposed research is significant because it is expected to show that Mtb requires ESX-5 activity for pathogenesis. This knowledge would establish ESX-5 as a strategic target for development of new anti-tubercular drugs and support inclusion of ESX-5-secreted antigens in new tuberculosis vaccines.