Abstract：
Mycobacteria are microorganisms distributed in the environment worldwide, and some of them, such as Mycobacterium tuberculosis or M. leprae, are pathogenic. The hydrophobic mycobacterial cell envelope has low permeation and bacteria need to export products across their structure. Mycobacteria possess specialized protein secretion systems, such as the Early Secretory Antigenic Target 6 secretion (ESX) system. Five ESX loci have been described in M. tuberculosis, called ESX-1 to ESX-5. The ESX-3 secretion system has been associated with mycobacterial metabolism and growth. The locus of this system is highly conserved across mycobacterial species. Metallo-proteins regulate negative ESX-3 transcription in high conditions of iron and zinc. Moreover, this secretion system is part of an antioxidant regulatory pathway linked to Zinc. EccA3, EccB3, EccC3, EccD3, and EccE3 are components of the ESX-3 secretion machinery, whereas EsxG-EsxH, PE5-PPE4, and PE15-PPE20 are proteins secreted by this system. In addition, EspG3 and MycP3 are complementary proteins involved in transport and proteolysis respectively. This system is associated to mycobacterial virulence by releasing the bacteria from the phagosome and inhibiting endomembrane damage response. Furthermore, components of this system inhibit the host immune response by reducing the recognition of M. tuberculosis-infected cells. The components of the ESX-3 secretion system play a role in drug resistance and cell wall integrity. Moreover, the expression data of this system indicated that external and internal factors affect ESX-3 locus expression. This review provides an overview of new findings on the ESX-3 secretion system, its regulation, expression, and functions.
摘要：
分枝杆菌是分布在全球环境中的微生物，其中一些，如结核分枝杆菌或麻风分枝杆菌，是致病性的。疏水性分枝杆菌细胞包膜具有低渗透性,并且细菌需要在其结构中输出产品。分枝杆菌拥有专门的蛋白质分泌系统，例如早期分泌抗原靶6分泌(ESX)系统。已经在结核分枝杆菌中描述了五个ESX基因座，称为ESX1到ESX5。ESX3分泌系统与分枝杆菌代谢和生长有关。该系统的基因座在分枝杆菌物种中高度保守。金属蛋白在铁和锌的高条件下调节负ESX3转录。此外，这种分泌系统是与锌相关的抗氧化剂调节途径的一部分。EccB3，EccC3，EccD3和EccE3是ESX3分泌机制的组成部分，而EsxG-EsxH,PE5-PPE4和P15-PPE20是该系统分泌的蛋白质。此外,EspG3和MycP3是分别参与转运和蛋白水解的互补蛋白。该系统通过从吞噬体释放细菌并抑制内膜损伤反应而与分枝杆菌毒力相关。此外，该系统的组分通过减少结核分枝杆菌感染的细胞的识别来抑制宿主的免疫应答。ESX3分泌系统的成分在耐药性和细胞壁完整性中起作用。此外，该系统的表达数据表明外部和内部因素影响ESX3基因座的表达。这篇综述概述了ESX3分泌系统的新发现，其规定,表达式,和功能。
