SsaM and SpiC interact and regulate secretion of Salmonella Pathogenicity Island 2 type III secretion system effectors and translocators
SsaM and SpiC interact and regulate secretion of Salmonella Pathogenicity Island 2 type III secretion system effectors and translocators
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DOI：
10.1111/j.1365-2958.2004.04297.x
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发表时间：
2004-11-01
影响因子：
3.6
通讯作者：
Holden, DW
中科院分区：
文献类型：
--
作者：
Yu, XJ;Liu, M;Holden, DW
由沙门氏菌致病性岛 2 (SPI-2) 编码的 III 型分泌系统 (TTSS) 是鼠伤寒沙门氏菌全身感染和细胞内复制所必需的。 SPI-2 TTSS 在细菌被宿主细胞内化后被激活，并将效应蛋白易位进入并穿过液泡膜，在那里它们干扰多种宿主细胞功能。在这里，我们研究了 SsaM（SPI-2 内编码的一种小蛋白质）的功能。 ssaM 缺失突变体的毒力和细胞内复制缺陷与 SPI-2 TTSS 无效突变体相当。尽管ssaM突变体能够在体外分泌效应蛋白SseJ，但它未能将SseJ易位到宿主细胞中，并在体外分泌易位子蛋白SseB、SseC和SseD。这种表型与携带 SPI-2 基因 spiC 突变的菌株相似，据报道其产物是参与巨噬细胞中沙门氏菌液泡运输的效应物。 ssaM 和 spiC 突变体均被发现在体外过度分泌 SPI-2 效应蛋白 SseJ 和 PipB。使用分级分析和免疫荧光显微镜来研究 SsaM 和 SpiC 在巨噬细胞中的定位。没有获得这些蛋白质易位的证据。 ssaM 和 spiC 突变体的相似表型表明它们可能参与相同的功能。 Pull-down 和共免疫沉淀实验表明 SpiC 和 SsaM 在细菌细胞内相互作用。我们提出，涉及 SsaM 和 SpiC 的复合物可区分易位蛋白和效应蛋白，并通过 SPI-2 TTSS 控制它们的有序分泌。
The type III secretion system (TTSS) encoded by Salmonella Pathogenicity Island 2 (SPI-2) is required for systemic infection and intracellular replication of Salmonella enterica serovar Typhimurium. The SPI-2 TTSS is activated after internalization of bacteria by host cells, and translocates effector proteins into and across the vacuolar membrane, where they interfere with several host cell functions. Here, we investigated the function of SsaM, a small protein encoded within SPI-2. An ssaM deletion mutant had virulence and intracellular replication defects comparable to those of a SPI-2 TTSS null mutant. Although the ssaM mutant was able to secrete the effector protein SseJ in vitro, it failed to translocate SseJ into host cells, and to secrete the translocon proteins SseB, SseC and SseD in vitro. This phenotype is similar to that of a strain carrying a mutation in the SPI-2 gene spiC, whose product is reported to be an effector involved in trafficking of the Salmonella vacuole in macrophages. Both ssaM and spiC mutants were found to oversecrete the SPI-2 effector proteins SseJ and PipB in vitro. Fractionation assays and immunofluorescence microscopy were used to investigate the localization of SsaM and SpiC in macrophages. No evidence for translocation of these proteins was obtained. The similar phenotypes of the ssaM and spiC mutants suggested that they might be involved in the same function. Pull-down and co-immune precipitation experiments showed that SpiC and SsaM interact within the bacterial cell. We propose that a complex involving SsaM and SpiC distinguishes between translocators and effector proteins, and controls their ordered secretion through the SPI-2 TTSS.