The putative invasion protein chaperone SicA acts together with InvF to activate the expression of Salmonella typhimurium virulence genes
The putative invasion protein chaperone SicA acts together with InvF to activate the expression of Salmonella typhimurium virulence genes
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DOI：
10.1046/j.1365-2958.2000.01772.x
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发表时间：
2000-02-01
影响因子：
3.6
通讯作者：
Miller, VL
中科院分区：
文献类型：
--
作者：
Darwin, KH;Miller, VL
SigD 和 SigE（沙门氏菌侵入基因）是鼠伤寒沙门氏菌在体外最佳侵入真核细胞所需的蛋白质。 SigD 是一种分泌蛋白，SigE 是 SigD 稳定性和/或分泌所需的假定伴侣。 SigD 由沙门氏菌染色体上称为沙门氏菌致病性岛 1 (SPI1) 的致病性岛内编码的 III 型分泌装置分泌。 sigDE 的表达与 SPI1 无关，与 SPI1 基因协同调节，并依赖于转录调节因子 SirA、HilA 和 InvF。单独这三种蛋白无法激活大肠杆菌中 sigD 启动子的转录，因此可能需要其他因子才能表达。对 sigD-lacZYA 报告基因融合表达所需基因的筛选发现了在 spaS 中插入转座子的突变体，spaS 是一种 SPI1 基因，编码 III 型分泌系统的假定内膜成分。在该突变体中，编码假定伴侣 (SicA) 和几种分泌蛋白 (Sips B、C、D 和 A) 的 SPI1 操纵子的表达也有所减少。 spaS突变体的调节缺陷由sicA而不是spaS来补充。由于 sicA 紧邻 spaS 下游编码，因此 spaS 中的突变可能对 sicA 的表达呈极性。此外，sicA 破坏突变体与 invF 缺失突变体一样，在 sigD、sicA 和 sipC 报告基因融合体的表达方面存在缺陷。将编码 invF 和 sicA 的质粒引入非致病性大肠杆菌 K-12 菌株中，刺激了 sicA- 和 sigD-lacZYA 启动子融合体的转录。该结果表明InvF和SicA足以表达这些基因。这是首次证明假定的 III 型分泌系统伴侣在毒力基因表达中的积极调节作用。
SigD and SigE (Salmonella invasion gene) are proteins needed for optimal invasion of Salmonella typhimurium into eukaryotic cells in vitro. SigD is a secreted protein and SigE is a putative chaperone required for SigD stability and/or secretion. SigD is secreted by a type III secretion apparatus encoded within a pathogenicity island on the Salmonella chromosome known as Salmonella pathogenicity island 1 (SPI1). The expression of sigDE, which is not linked to SPI1, is co-ordinately regulated with the SPI1 genes and is dependent on the transcriptional regulators SirA, HilA and InvF. These three proteins alone are unable to activate transcription from the sigD promoter in Escherichia coli, therefore it is likely that other factors are needed for expression. A screen for genes required for the expression of a sigD-lacZYA reporter fusion found a mutant with a transposon insertion in spaS, an SPI1 gene which encodes a putative inner-membrane component of the type III secretion system. The expression of a SPI1 operon encoding a putative chaperone (SicA) and several secreted proteins (Sips B, C, D and A) was also reduced in this mutant. The regulation defect of the spaS mutant was complemented by sicA and not by spaS. Because sicA is encoded immediately downstream of spaS, the mutation in spaS was likely to be polar on the expression of sicA. In addition, a sicA disruption mutant was as defective as an invF deletion mutant for the expression of sigD, sicA and sipC reporter fusions. The introduction of plasmids encoding invF and sicA into a non-pathogenic E. coli K-12 strain stimulated the transcription of both a sicA- and a sigD-lacZYA promoter fusion. This result suggests that InvF and SicA are sufficient for the expression of these genes. This is the first demonstration of a positive regulatory role for a putative type III secretion system chaperone in the expression of virulence genes.