Small molecule control of virulence gene expression in Francisella tularensis.
Small molecule control of virulence gene expression in Francisella tularensis.
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DOI：
10.1371/journal.ppat.1000641
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发表时间：
2009-10
期刊：
影响因子：
6.7
通讯作者：
Dove SL
中科院分区：
文献类型：
--
作者：
Charity JC;Blalock LT;Costante-Hamm MM;Kasper DL;Dove SL
在土拉热弗朗西丝菌中，SspA蛋白家族成员MglA和SspA形成与RNA聚合酶（RNAP）相关联的复合物，以积极控制对生物体的巨噬细胞内生长和存活至关重要的毒力基因的表达。尽管MglA-SspA复合物与RNAP的结合对于其在控制基因表达中的作用显然是至关重要的，但MglA和SspA如何发挥其作用的分子细节尚不清楚。在这里，我们表明，在活疫苗株的F。在土拉热菌（LVS）中，MglA-SspA复合物与我们称为PigR的推定DNA结合蛋白以及alarmone鸟苷四磷酸（ppGpp）一起协同作用，以调节靶基因的表达。特别是，我们提出的证据表明，MglA，SspA，PigR和ppGpp调节同一组基因的表达，并表明，MglA，SspA，PigR和ppGpp无效突变体表现出类似的巨噬细胞内生长缺陷，并强烈减弱小鼠的毒力。我们进一步表明PigR直接与MglA-SspA复合物相互作用，表明MglA和SspA蛋白在控制毒力基因表达中的核心作用是作为转录激活因子的靶点。最后，我们提出的证据表明，ppGpp发挥其作用，促进PigR和RNAP相关的MglA-SspA复合物之间的相互作用。通过其对ppGpp的响应性，PigR与MglA-SspA复合物之间的接触允许将营养线索整合到支配毒力基因表达的调控网络中。鸟苷四磷酸（ppGpp）是一种小分子，由许多不同的细菌响应营养限制而产生。虽然ppGpp已被证明在控制几种病原菌的毒力基因的表达中发挥重要作用，但很少有研究涉及这是如何发生的。在这里，我们表明，在胞内病原体F。tularensis中，ppGpp在控制细胞内复制和毒力所需的基因表达方面起着关键作用，我们揭示了其作用的分子基础。特别是，我们表明ppGpp与其他三个重要的毒力基因表达调节因子在F。土拉热-一种假定的DNA结合蛋白，我们称之为PigR和SspA蛋白家族成员MglA和SspA。我们的研究提供了证据，ppGpp功能，以促进PigR和F的一个组成部分之间的相互作用。在一些实施方案中，本发明涉及包含MglA和SspA蛋白的土拉热菌RNA聚合酶（RNAP）。通过影响PigR和RNAP相关的MglA-SspA复合物之间的相互作用，ppGpp用于将细胞的营养状态与宿主中生存所必需的基因的表达联系起来。
In Francisella tularensis, the SspA protein family members MglA and SspA form a complex that associates with RNA polymerase (RNAP) to positively control the expression of virulence genes critical for the intramacrophage growth and survival of the organism. Although the association of the MglA-SspA complex with RNAP is evidently central to its role in controlling gene expression, the molecular details of how MglA and SspA exert their effects are not known. Here we show that in the live vaccine strain of F. tularensis (LVS), the MglA-SspA complex works in concert with a putative DNA-binding protein we have called PigR, together with the alarmone guanosine tetraphosphate (ppGpp), to regulate the expression of target genes. In particular, we present evidence that MglA, SspA, PigR and ppGpp regulate expression of the same set of genes, and show that mglA, sspA, pigR and ppGpp null mutants exhibit similar intramacrophage growth defects and are strongly attenuated for virulence in mice. We show further that PigR interacts directly with the MglA-SspA complex, suggesting that the central role of the MglA and SspA proteins in the control of virulence gene expression is to serve as a target for a transcription activator. Finally, we present evidence that ppGpp exerts its effects by promoting the interaction between PigR and the RNAP-associated MglA-SspA complex. Through its responsiveness to ppGpp, the contact between PigR and the MglA-SspA complex allows the integration of nutritional cues into the regulatory network governing virulence gene expression. Guanosine tetraphosphate (ppGpp) is a small molecule that is produced by many different bacteria in response to nutrient limitation. Although ppGpp has been shown to play an important role in controlling the expression of virulence genes in several pathogenic bacteria, few studies have addressed how this occurs. Here we show that in the intracellular pathogen F. tularensis, ppGpp plays a critical role in controlling the expression of genes required for intracellular replication and virulence, and we uncover the molecular basis for its effect. In particular, we show that ppGpp works in concert with three other essential regulators of virulence gene expression in F. tularensis—a putative DNA-binding protein that we have called PigR and the SspA protein family members MglA and SspA. Our study provides evidence that ppGpp functions to promote the interaction between PigR and a component of F. tularensis RNA polymerase (RNAP) comprising the MglA and SspA proteins. By influencing the interaction between PigR and the RNAP-associated MglA-SspA complex, ppGpp serves to tie the nutritional status of the cell to the expression of genes that are essential for survival in the host.
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