pH-dependent secretion of SseB, a product of the SPI-2 type III secretion system of Salmonella typhimurium
pH-dependent secretion of SseB, a product of the SPI-2 type III secretion system of Salmonella typhimurium
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DOI：
10.1046/j.1365-2958.1999.01527.x
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发表时间：
1999-08-01
影响因子：
3.6
通讯作者：
Holden, DW
中科院分区：
文献类型：
--
作者：
Beuzón, CR;Banks, G;Holden, DW
沙门氏菌致病性岛2 (SPI-2) III型分泌系统是细菌在巨噬细胞内复制所必需的。SseB;由于其与肠致病性大肠杆菌（EPEC） III型分泌系统分泌的蛋白EspA相似，被认为是分泌系统的假定靶点。EspA在细菌细胞表面形成丝状结构，并参与蛋白质转运到真核细胞质中。在本文中，我们发现SseB是一种与细菌细胞表面结合的分泌蛋白，因此可能也需要将SPI-2效应蛋白递送到真核细胞的细胞质中。SseB开始在细菌细胞内积累，当培养进入早期稳定期。然而，SseB只有在细菌在低pH下生长或pH从7.0转移到低于pH 5.0时才会分泌。这种分泌在酸化后几分钟内发生，完全依赖于功能性的SPI-2 III型分泌系统。由于宿主细胞内含沙门氏菌液泡的pH值已被证明在pH4.0 - 5.0之间酸化，并且宿主细胞内存在SPI-2基因表达，因此低pH值可能是体内SPI-2介导分泌的生理刺激。
The type III secretion system of Salmonella pathogenicity island 2 (SPI-2) is required for bacterial replication inside macrophages. SseB has; been considered a putative target of the secretion system on the basis of its similarity with EspA, a protein secreted by the type III secretion system of enteropathogenic Escherichia coli (EPEC). EspA forms a filamentous structure on the bacterial cell surface and is involved in translocation of proteins into the eukaryotic cytosol. In this paper, we show that SseB is a secreted protein that associates with the surface of the bacterial cell and might, therefore, also be required for delivery of SPI-2 effector proteins to the eukaryotic cell cytosol. SseB begins to accumulate inside the bacterial cell when the culture enters early stationary phase. However, SseB is only secreted if the bacteria are grown at low pH or if the pH is shifted after growth from 7.0 to below pH 5.0. The secretion occurs within minutes of acidification and is totally dependent on a functional SPI-2 type III secretion system. As the pH of the Salmonella-containing vacuole inside host cells has been shown to acidify to between pH4.0 and 5.0, and as SPI-2 gene expression occurs inside host cells, low pH might be a physiological stimulus for SPI-2-mediated secretion in vivo.